ill 
 
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 Book ' S ^ — 
 
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SOILS AND FERTILIZERS 
 
THE MACMILLAN COMPANY 
 
 NEW YORK • BOSTON • CHICAGO 
 ATLANTA • SAN FRANCISCO 
 
 MACMILLAN & CO., Limited 
 
 LONDON ■ BOMBAY ■ CALCUTTA 
 MELBOURNE 
 
 THE MACMILLAN CO. OF CANADA, Ltd. 
 
 TORONTO 
 
SOILS AND FERTILIZERS 
 
 BY 
 
 HARRY SNYDER, B.S. 
 
 PROFESSOR OF AGRICULTURAL CHEMISTRY AND SOILS 
 UNIVERSITY OF MINNESOTA 
 
 THIRD EDITION 
 
 THE MACMILLAN COMPANY 
 1908 
 
 , All rights reserved 
 
UBWARV of CONGRESS 
 I wo Oooies neceotxi 
 
 JUN 23 iy08 
 
 OLASS A \XC. Nv 
 
 COPY B. 
 
 b' 
 
 
 ^^ 
 
 Copyright, 1908, 
 By the MACMILLAN COMPANY. 
 
 Set up and electrotyped. Published June, 1908. 
 
 J. S. Gushing Co. — Berwick & Smith Co. 
 Norwood, Mass., U.S.A. 
 
PREFACE TO THIRD EDITION 
 
 This work is the outgrowth of instruction given at 
 the University of Minnesota to young men who intend 
 to become farmers and who desire information that will 
 be of assistance to them in their profession. At first 
 mimeographed notes were prepared, which were later 
 published under the title " The Chemistry of Soils and 
 Fertilizers." This was revised, enlarged, and published 
 as " Soils and Fertilizers." With the extension of 
 various lines of investigation relating to soils, a sec- 
 ond revision and enlargement of the book has become 
 necessary. It is the aim to present in condensed form 
 the principles of the various sciences, particularly chem- 
 istry, which have a bearing upon the economic produc- 
 tion of crops and the conservation of the soil's fertility. 
 The work as now presented includes all the topics 
 and the laboratory experiments relating to soils, as out- 
 lined by the Committee on Methods of Teaching Agri- 
 culture, of the Association of Agricultural Colleges and 
 Experiment Stations. 
 
 HARRY SNYDER. 
 
 University of Minnesota, 
 College of Agriculture, 
 
 St. Anthony Park, Minnesota, 
 
 March i, 1908. 
 
CONTENTS 
 
 PAGES 
 
 Introduction i-io 
 
 Early uses of manures and explanation of their action 
 by alchemists ; Investigations prior to 1800 : Work of De 
 Saussure, Davy, Thaer, and Boussingault ; Liebig's writ- 
 ings and their influence ; Investigations of Lawes and Gil- 
 bert ; Work of Tull ; Contributions of other investigators ; 
 Agronomy; Value of soil studies. 
 
 CHAPTER I 
 
 Physical Properties of Soils 11-53 
 
 Chemical and physical properties of soils considered ; 
 Weight of soils ; Pore space ; Specific gravity ; Size of soil 
 particles ; Clay ; Sand ; Silt ; Form of soil particles ; Num- 
 ber and arrangement of soil particles ; Mechanical analysis 
 of soils ; Crop growth and physical properties. Soil types : 
 Potato and truck soils ; FrUit soils ; Corn soils ; Me- 
 dium grass and grain soils ; Wheat soils ; Sandy, clay, 
 and loam soils. Relation of the soil to water ; Amount of 
 water required for crops ; Bottom water ; Capillary water ; 
 Hydroscopic water ; Loss of water by percolation, evapo- 
 ration, and transpiration ; Drainage ; Influence of forest 
 regions ; Influence of cultivation upon the water supply 
 of crops ; Capillary water and cultivation ; Shallow surface 
 cultivation ; Cultivation after rains ; Rolling ; Subsoiling ; 
 Fall plowing; Spring plowing; Mulching; Depth of 
 plowing ; Permeabijity of soils ; Fertilizers and their in- 
 
Viii CONTENTS 
 
 PAGES 
 
 fluence upon moisture content of soils ; Farm manures 
 and soil moisture ; Relation of soils to heat ; Heat re- 
 quired for evaporation ; Influence of drainage upon soil 
 temperature ; Specific heat of soils ; Cultivation and soil 
 temperature ; Heat from chemical reactions within the 
 soil ; Heat and crop growth ; Organic matter and iron 
 compounds; Color of soils ; Odorand taste of soils ; Power 
 to absorb gases ; Relation of soils to electricity ; Impor- 
 tance of physical properties of the soil. 
 
 CHAPTER II 
 
 Geological Formation and Classification of Soils 54-70 
 Agricultural geology ; Formation of soils ; Action of 
 heat and cold ; Action of water ; Glacial action ; Chem- 
 ical action of water ; Action of air and gases ; Action of 
 microorganism ; Action of vegetation ; Action of earth- 
 worms ; Action of wind ; Combined action of the various 
 agents ; Distribution of soils ; Sedentary and transported 
 soils ; Rocks and minerals from which soils are derived, 
 as quartz, feldspar, mica, hornblende, zeolites, granite, 
 apatite, limestone, kaolin ; Disintegration of rocks and 
 minerals ; Value of geological study of soils. 
 
 CHAPTER III 
 
 The Chemical Composition of Soils . . . 71-115 
 Elements present in soils ; Classification of elements ; 
 Combination of elements ; Forms in which elements are 
 present in soils ; Acid-forming elements, silicon, double 
 silicates, carbon, sulphur, chlorine, phosphorus, nitrogen, 
 oxygen, hydrogen ; Base-forming elements, aluminum, 
 potassium, calcium, magnesium, sodium, iron ; Forms of 
 plant food ; Amount of plant food in different forms in 
 
CONTENTS IX 
 
 . PAGES 
 
 various types of soils ; Acid soluble matter of soils ; Acid 
 insoluble matter ; Action of organic acids upon soils ; How 
 a soil analysis is made ; Value of soil analysis ; Interpre- 
 tation of the results of soil analysis ; Use of dilute acids 
 as solvents in soil analysis ; Use of dilute mineral acids in 
 soil analysis ; Available and unavailable plant food ; Vola- 
 tile matter of soils ; Distribution of plant food in the soil ; 
 Composition of typical soils ; ' Alkali ' soils and their 
 improvement ; Acid soils ; Organic compounds of soil ; 
 Sources ; Classification ; Humus ; Humates ; Humifica- 
 tion ; Humates produced by different kinds of organic 
 matter; Mineral matter combined with humus; Value of 
 humates as plant food ; Amount of plant food in humic 
 forms ; Physical properties of soils influenced by humus ; 
 Loss of humus by forest fires, by prairie fires, by cultiva- 
 tion ; Humic acid ; Soils in need of humus ; Soils not in 
 need of humus ; Composition of humus from old and new 
 soils; Influence of different methods of farming upon 
 humus. 
 
 CHAPTER IV 
 
 Nitrogen of the Soil and Air, Nitrification, and Ni- 
 trogenous Manures 1 16-157 
 
 Importance of nitrogen as plant food ; Atmospheric ni- 
 trogen as a source of plant food. Experiments of Bous- 
 singault, Ville, Lawes and Gilbert, and Atwater ; Result 
 of field trials ; Experiments of Hellriegel and Wilfarth 
 and recent investigators ; Composition of root nodules ; 
 Amount of nitrogen returned to soil by leguminous crops 
 and importance to agriculture ; Nitrogenous compounds 
 of the soil ; Origin ; Organic nitrogen ; Amount of nitro- 
 gen in soils ; Removed in crops ; Nitrates and nitrites ; 
 Ammonium compounds ; Ammonia in rain and drain 
 
X CONTENTS 
 
 PAGES 
 
 waters ; Ratio of nitrogen to carbon in the soil ; Losses 
 of nitrogen from soils ; Gains of nitrogen to soils ; Nitri- 
 fication : Former views regarding ; Workings of an organ- 
 ism ; Conditions necessary for nitrification ; Influence of 
 cultivation upon these conditions ; Nitrous acid organisms, 
 ammonia-producing organisms, denitrification, number and 
 kind of organisms in soils ; Inoculation of soils with 
 organisms ; Chemical products produced by organisms ; 
 Losses of nitrogen by fallowing rich prairie lands ; Influ- 
 ence of plowing upon nitrification ; Nitrogenous manures ; 
 Sources ; Dried blood, tankage, flesh meal, fish scrap, 
 seed residue, and uses of each ; Leather, wool waste, and 
 hair ; Available organic nitrogen ; Peat and muck ; Le- 
 guminous crops as nitrogenous fertilizers ; Sodium nitrate, 
 ammonium salts ; Calcium cyanamid ; Cost and value of 
 nitrogenous fertilizers. 
 
 CHAPTER V 
 
 Farm Manures 158-190 
 
 Variable composition of farm manures ; Average com- 
 position of manures ; Factors which influence composition 
 of manures ; Absorbents ; Use of peat and muck as ab- 
 sorbents ; Relation of food consumed to manures pro- 
 duced ; Bulky and concentrated foods ; Course of the 
 nitrogen of the food during digestion ; Composition of 
 liquid and solid excrements ; Manurial value of foods ; 
 Commercial valuation of manure ; Influence of age and 
 kind of animal ; Manure from young and old animals ; 
 Cow manure ; Horse manure ; Sheep manure ; Hog ma- 
 nure; Hen manure ; Mixing manures ; Volatile products 
 from manure ; Human excrements ; Preservation of ma- 
 nures ; Leaching ; Losses by fermentation ; Different kinds 
 of fermentation ; Water necessary for fermentation ; Heat 
 
CONTENTS XI 
 
 PAGES 
 
 produced during fermentation ; Composting manures ; 
 Uses of preservatives ; Manure produced in sheds ; Value 
 of protected manure ; Use of manures ; Direct hauling to 
 field ; Coarse manures injurious ; Manuring pasture land ; 
 Small piles of manure in fields objectionable ; Rate of 
 application ; Most suitable crops to apply to ; Compara- 
 tive value of manure and food ; Lasting effects of manure ; 
 Comparative value of good and poor manure ; Summary 
 of ways in which manures may be beneficial. 
 
 CHAPTER VI 
 
 Fixation igi-197 
 
 Fixation a chemical change, examples of; Fixation and 
 absorption ; Due to zeolites ; Humus and fixation ; Soils 
 possess diff"erent powers of fixation ; Nitrates do not 
 undergo fixation ; Fixation of potash, phosphoric acid, 
 and ammonia ; Fixation may make plant food less avail- 
 able ; Fixation a desirable property of soils ; Fixation and 
 the action of manures ; Fixation and soil solution. 
 
 CHAPTER VII 
 
 Phosphate Fertilizers 198-2 11 
 
 Importance of phosphorus as plant food ; Amount re- 
 moved in crops ; Amount and source of phosphoric acid 
 in soils ; Commercial forms of phosphoric acid ; Phosphate 
 rock ; Calcium phosphates ; Reverted phosphoric acid ; 
 Available phosphoric acid ; Manufacture of phosphate 
 fertilizers, acid phosphates, superphosphates ; Commercial 
 value of phosphoric acid ; Basic slag phosphate ; Guano ; 
 Bones ; Steamed bone ; Dissolved bone ; Bone black ; 
 Fineness of division of phosphate fertilizers ; Use of 
 phosphate fertilizers ; How to keep the phosphoric acid 
 of the soil available. 
 
Xii CONTENTS 
 
 CHAPTER VIII 
 
 PAGES 
 
 Potash Fertilizers 212-222 
 
 Potassium an essential element ; Amount of potash re- 
 moved in crops ; Amount in soils ; Source of soil potash ; 
 Commercial forms of potash ; Stassfurt salts, occurrence 
 of; Kainit; Muriate of potash ; Sulphate of potash ; Other 
 Stassfurt salts; Wood ashes, composition of; Amount of 
 ash in different kinds of wood ; Action of ashes on soils ; 
 Leached ashes ; The alkalinity of ashes ; Coal ashes ; 
 Miscellaneous ashes ; Commercial value of potash ; Use 
 of potash fertilizers ; Joint use of potash and lime. 
 
 CHAPTER IX 
 
 Lime and Miscellaneous Fertilizers . . . 223-232 
 Calcium an essential element ; Amount of lime removed 
 in crops ; Amount of lime in soils ; Different kinds of 
 Hme fertilizers ; Their physical and chemical action ; Action 
 of lin.e upon organic matter and in correcting acidity of 
 soils ; Lime liberates potash ; Aids nitrification ; Action of 
 land plaster on some ' alkali ' soils ; Quicklime and slaked 
 lime ; Pulverized lime rock ; Marl ; Physical action of 
 lime; Judicious use of lime; Miscellaneous fertilizers; 
 Salt and its action on the soil ; Magnesium salts ; Soot ; 
 Seaweed ; Strand plant ash ; Wool washings ; Street 
 sweepings. 
 
 CHAPTER X 
 
 Commercial Fertilizers 233-254 
 
 History of development of industry ; Complete fertili- 
 zers and amendments ; Variable composition of commer- 
 cial fertilizers ; Preparation of fertilizers ; Inert forms of 
 
CONTENTS Xm 
 
 matter in fertilizers ; Inspection of fertilizers ; Mechanical 
 condition of fertilizers ; Forms of nitrogen, phosphoric 
 acid, and potash in commercial fertilizers ; Misleading 
 statements on fertilizer bags ; Estimating the value of a 
 fertilizer ; Home mixing ; Fertilizers and tillage ; Abuse 
 of commercial fertilizers; Judicious use of; Field tests; 
 Preliminary experiments ; Verif3^ing results ; Deficiency 
 of nitrogen, phosphoric acid, potash, and of two elements ; 
 Importance of field trials; Will it pay to use fertilizers? 
 Amount to use per acre ; Influence of excessive applica- 
 tions ; Fertilizing special crops ; Commercial fertilizers 
 and farm manures. 
 
 CHAPTER XI 
 
 Food Requirements of Crops 255-272 
 
 Amount of fertility removed by crops ; Assimilative 
 powers of crops compared ; Ways in which plants obtain 
 their food ; Cereal crops, general food requirements ; 
 Wheat; Barley; Oats; Corn; Miscellaneous crops ; Flax; 
 Potatoes ; Sugar beets ; Roots ; Turnips ; Rape ; Buck- 
 wheat ; Cotton ; Hops ; Hay and grass crops ; Leguminous 
 crops ; Garden crops ; Fruit trees ; Small fruits ; Lawns. 
 
 CHAPTER XII 
 
 Rotation of Crops and Conservation of Soil Fer- 
 tility 273-290 
 
 Object of rotating crops ; Principles involved in crop 
 rotation ; Deep- and shallow-rooted crops ; Humus-con- 
 suming and humus-producing crops ; Crop residues ; Ni- 
 trogen-consuming and nitrogen-producing crops ; Rotation 
 and mechanical condition of soil ; Economic use of soil 
 water ; Rotation and farm labor ; Economic use of ma- 
 nures ; Salable crops ; Rotations advantageous in other 
 
XIV CONTENTS 
 
 PAGES 
 
 ways ; Long- and short-course rotations ; Example of 
 rotation ; Problems in rotations ; Conservation of fertility ; 
 Necessity of manures ; Use of crops ; Two systems of 
 farming compared ; Losses of fertility with different 
 methods of farming ; Problems on income and outgo of 
 fertility from farms. 
 
 CHAPTER XIII 
 
 Preparation of Soils for Crops .... 291-306 
 Importance of good physical condition of seed bed ; In- 
 fluence of methods of plowing upon the condition of the 
 seed bed ; Influence of moisture content of the soil at the 
 time of plowing; Influence upon the seed bed of pulver- 
 izing and fining the soil ; Aeration of seed bed necessary ; 
 Preparation of seed bed without plowing ; Mixing of sub- 
 soil with seed bed ; Cultivation to destroy weeds ; Influ- 
 ence of cultivation upon bacterial action ; Cultivation for 
 special crops ; Cultivation to prevent washing and gully- 
 ing of lands ; Bacterial diseases of soils ; Influence of 
 crowding of plants in the seed bed ; Selection of crops ; 
 Inherent and cumulative fertility of soils ; Balanced soil 
 conditions. 
 
 CHAPTER XIV 
 
 Laboratory Practice 307-326 
 
 General directions ; Note book ; Apparatus used in 
 work ; Determination of hydroscopic moisture of soils ; 
 Determination of the volatile matter ; Determination of 
 the capacity of loose soils to absorb water ; Determination 
 of capillary water of soils ; Capillary action of water upon 
 soils ; Influence of manure and shallow surface cultivation 
 upon moisture content and temperature of soils ; Weight 
 
CONTENTS XV 
 
 PAGES 
 
 of soils ; Influence of color upon the temperature of soils ; 
 Rate of movement of air through soils ; Rate of move- 
 ment of water through soils ; Separation of sand, silt, and 
 clay; Sedimentation of clay; Properties of rocks from 
 which soils are derived ; Form and size of soil par- 
 ticles ; Pulverized rock particles ; Reaction of soils ; The 
 granulation of soils ; Absorption of gases by soils ; Acid 
 insoluble matter of soils ; Acid soluble matter of soils ; 
 Extraction of humus from soils ; Nitrogen in soils ; Test- 
 ing for nitrates ; Volatilization of ammonium salts ; Test- 
 ing for phosphoric acid ; Preparation of acid phosphate ; 
 Solubility of organic nitrogenous compounds in pepsin 
 solution ; Preparation of fertilizers ; Testing ashes ; Ex- 
 tracting water soluble materials from a commercial fertili- 
 zer ; Influence of continuous cultivation and crop rotation 
 upon the properties of soil ; Summary of results with tests 
 of home soil. i 
 
 Review Questions 327-339 
 
 References 340-344 
 
 Index 345-35° 
 
SOILS AND FERTILIZERS 
 
 INTRODUCTION 
 
 Prior to 1800 but little was known of the sources 
 and importance of plant food. Manures had been 
 used from the earliest times, and their value was recog- 
 nized, although the fundamental principles underlying 
 their use were not understood. It was believed they 
 acted in some mysterious way. The alchemists had 
 advanced various views regarding them ; one was that 
 the so-called " spirits " left the decaying manure and 
 entered the plant, producing more vigorous growth. 
 As evidence, the worthless character of leached manure 
 was cited. It was thought the spirits had left such 
 manure. The terms 'spirits of hartshorn,' 'spirits of 
 niter,' ' spirits of turpentine,' and many others reflect 
 these ideas regarding the composition of matter. 
 
 The alchemists held that one substance, as copper, 
 could be changed to another substance, as gold. Plants 
 were supposed to be water transmuted in some myste- 
 rious way directly into plant tissue. Van Helmont, in 
 the seventeenth century, attempted to prove this. " He 
 took a large earthen vessel and filled it with 200 
 pounds of dried earth. In it he planted a willow 
 
2 SOILS AND FERTILIZERS 
 
 weighing 5 pounds, which he duly watered with rain 
 and distilled water. After five years he pulled up the 
 willow and it now weighed 169 pounds and 3 ounces."^ 
 He concluded that 164 pounds of roots, bark, leaves, 
 and branches had been produced by direct transmu- 
 tation of the water. 
 
 It is evident from the preceding example that any- 
 thing like an adequate idea of the growth and compo- 
 sition of plant bodies could not be gained until the 
 composition of air and water was established. 
 
 The discovery of oxygen by Priestley in 1774, of 
 the composition of water by Cavendish in 1781, and 
 of the role which carbon dioxide plays in plant and 
 animal Hfe by De Saussure and others in 1800, formed 
 the nucleus of our present knowledge regarding the 
 sources of matter stored up in plants. It was between 
 1760 and 1800 that alchemy lost its grip because of 
 advances in knowledge and the way was opened for 
 the development of modern chemistry. 
 
 De Saussure's " Recherches sur la Vegetation," pub- 
 lished in 1804, was the first systematic work showing 
 the sources of the compounds stored up in plant bodies. 
 He demonstrated, quantitatively, that the increase in the 
 amount of carbon, hydrogen, and oxygen, when plants 
 were exposed to sunlight, was at the expense of the 
 carbon dioxide of the air, and of the water of the soil. 
 He also, maintained that the mineral elements derived 
 from the soil were essential for plant growth, and gave 
 the results of the analyses of many plant ashes. He 
 
INTRODUCTION 3 
 
 believed that the nitrogen of the soil was the main 
 source of the nitrogen found in plants. These views 
 have since been verified by many investigators, and are 
 substantially those held at the present time regarding 
 the fundamental principles of plant growth. They were 
 not, however, accepted as conclusive at the time, and it 
 was not until nearly a half-century later, when Bous- 
 singault, Liebig, and others repeated the investigations 
 of De Saussure, that they were finally accepted by chem- 
 ists and botanists. 
 
 From the time of De Saussure to 1835, scientific 
 experiments relating to plant growth were not actively 
 prosecuted, but the facts which had accumulated were 
 studied, and attempts were made to apply the results 
 to actual practice. Among the first to see the relation 
 between chemistry and agriculture was Sir Humphry 
 Davy. In 181 3 he published his "Essentials of Agri- 
 cultural Chemistry," which treated of the composition 
 of air, soil, manures, and plants, and of the influence 
 of light and heat upon plant growth. About this 
 period, Thaer published an important work entitled 
 " Principes Raisonnes d' Agriculture." He believed 
 humus determined the fertility of the soil, that plants 
 obtained their food mainly from humus, and that the 
 carbon compounds of plants were produced from the 
 organic carbon compounds of the soil. This gave rise 
 to the so-called humus theory, which was later shown 
 to be an inadequate idea regarding the source of plant 
 food, and for a time it prevented the actual value of 
 
4 SOILS AND FERTILIZERS 
 
 humus as a factor of soil fertility from being recog- 
 nized. The writings of Thaer were of a most prac- 
 tical nature, and they did much to stimulate later 
 investigations. 
 
 About 1830 there was renewed interest in scientific 
 investigations relating to agriculture. At this time 
 Boussingault, a French investigator, became actively 
 engaged in agricultural research. He was the first to 
 have a chemical laboratory upon a farm and to make 
 practical investigations in connection with agriculture. 
 This marks the establishment of the first agricultural 
 experiment station. Boussingault's work upon the as- 
 similation of the free nitrogen of the air is reviewed in 
 Chapter IV. His study of the rotation of crops was 
 a valuable contribution to agricultural science. He dis- 
 covered many important facts relating to the chemical 
 characteristics of foods, and was the first to make a 
 comparison as to the amount of nitrogen in differ- 
 ent kinds of foods and to determine their value on the 
 basis of the nitrogen content. His study of the pro- 
 duction of saltpeter did much to prepare the way for 
 later work on nitrification. The investigations of Bous- 
 singault covered a variety of subjects relating to plant 
 growth. He repeated and verified much of the earlier 
 work of De Saussure, and also secured many additional 
 facts regarding the chemistry of growth. As to the 
 source of nitrogen in crops, he states : " The soil fur- 
 nishes the crops with mineral alkaline substances, pro- 
 vides them with nitrogen, by ammonia and by nitrates, 
 
INTRODUCTION 5 
 
 which are formed in the soil at the expense of the nitrog- 
 enous matter contained in diluvium, which is the basis 
 of vegetable earth ; compounds in which nitrogen exists 
 in stable combination, only becoming fertilizing by the 
 effect of time." As to the absorption of the gaseous 
 nitrogen of the air by vegetable earth, he says : " I am 
 not acquainted with a single irreproachable observation 
 that establishes it ; not only does the earth not absorb 
 gaseous nitrogen, but it gives it off." ^ 
 
 The investigations of DeSaussure and Boussingault, 
 and the writings of Davy, Thaer, Sprengel, and Schiib- 
 ler prepared the way for the work and writings of Lie- 
 big. In 1840 he published "Organic Chemistry in its 
 Applications to Agriculture and Physiology." Liebig's 
 agricultural investigations were preceded by many valu- 
 able discoveries in organic chemistry, which he apphed 
 directly in his interpretations of agricultural problems. 
 His writings were of a forceful character and were ex- 
 tremely argumentative. They provoked, as he intended, 
 vigorous discussions upon agricultural problems. He 
 assailed the humus theory of Thaer, and showed that 
 humus was not an adequate source of the plant's carbon. 
 In the first edition of his work he noted that farms 
 from which certain products were sold became less pro- 
 ductive, because of the loss of nitrogen. In a second 
 edition he considered that the combined nitrogen of 
 the air was sufficient for crop production. He overesti- 
 mated the amount of ammonia in the air, and underesti- 
 mated the value of the nitrogen in soils and manures. 
 
6 SOILS AND FERTILIZERS 
 
 A Study of the composition of ash of plants led him 
 to propose the mineral theory of plant nutrition. 
 De Saussure had shown that plants contain certain min- 
 eral elements, but he did not emphasize their impor- 
 tance as plant food. Liebig's writings on the composi- 
 tion of plant ash, and his emphasizing the importance of 
 supplying crops with mineral food, led to the commer- 
 cial preparation of manures, which in later years devel- 
 oped into the commercial fertilizer industry. The work 
 of Liebig was not conducted in connection with field 
 experiments. It had, however, a most stimulating in- 
 fluence upon investigations in agricultural chemistry, 
 and to him we owe, in a great degree, the summarizing 
 of previous disconnected work and the mapping out of 
 valuable lines for future investigations. 
 
 Liebig's enthusiasm for agricultural investigations 
 may be judged from the following extract : " I shall be 
 happy if I succeed in attracting the attention of men 
 of science to subjects which so well merit to engage 
 their talents and energies. Perfect agriculture is the 
 true foundation of trade a7id industry ; it is the founda- 
 tion of the riches of states. But a rational system of 
 agriculture cannot be formed without the application of 
 scientific principles, for such a system must be based on 
 an exact acquaintance with the means of nutrition of 
 vegetables, and with the influence of soils, and actions 
 of manures upon them. This knowledge we must seek 
 from chemistry, which teaches the mode of investigat- 
 ing the composition and of the study of the character of 
 
INTRODUCTION 7 
 
 the different substances from which plants derive their 
 nourishment."^ 
 
 Soon after Liebig's first work appeared, the investi- 
 gations at Rothamsted by Sir J. B. Lawes were under- 
 taken. The most extensive systematic work in both 
 field experiments and laboratory investigations ever 
 conducted has been carried on by Lawes and Gilbert 
 at Rothamsted, Eng. Dr. Gilbert had previously been 
 a pupil of Liebig, and his becoming associated with 
 Sir J. B. Lawes marks the establishment of the second 
 experiment station. Many of the Rothamsted experi- 
 ments have been continued since 1844, and results of 
 the greatest value to agriculture have been obtained. 
 The investigations on the non-assimilation of atmos- 
 pheric nitrogen by crops, pubhshed in 1861, were ac- 
 cepted as conclusive evidence upon this much-vexed 
 question. Their work on manures, nitrification, the 
 nitrogen supply of crops, and the increase and decrease 
 of the nitrogen of the soil when different crops are pro- 
 duced, has had a most important bearing upon main- 
 taining the fertility of soils. 
 
 " The general plan of the field experiments has been 
 to grow some of the most important crops of rotation, 
 each separately, for many years in succession on the 
 same land, without manure, with farmyard manure, 
 and with a great variety of chemical manures, the 
 same kind of manure being, as a rule, applied year 
 after year on the same plot. Experiments with differ- 
 ent manures on the mixed herbage of permanent grass 
 
8 SOILS AND FERTILIZERS 
 
 land, on the effects of fallow, and on the actual course 
 of rotation without manure, and with different manures 
 have likewise been made."^ 
 
 In addition to Davy, Thaer, De Saussure, Boussin- 
 gault, Liebig, and Lawes and Gilbert, a great many 
 others have contributed to our knowledge of the prop- 
 erties of soils. The work of Pasteur, while it did not 
 directly relate to soils, indirectly had great influence 
 upon soil investigations. His researches upon fermen- 
 tation made it possible for Schlosing to prove that 
 nitrification is the result of the workings of living 
 organisms. These have since been isolated and studied 
 by Warington and Winogradsky. 
 
 The importance of the physical condition of the soil 
 and its relation to crop production was recognized by 
 agriculturists at about the same time that the sources 
 of plant food were being investigated. Jethro Tull 
 published in 1829 a work entitled "The Horse-Hoeing 
 Husbandry," which emphasized the importance of 
 thorough cultivation of the soil. That increase in the 
 yield of crops, destruction of weeds, reduction of rust 
 and blight of wheat, and general improvement of the 
 soil, are all results of improved tillage is clearly set 
 forth in Tull's work. Tull was inclined to believe that 
 tillage could take the place of manure. " All sorts of 
 dung and compost contain some matter which, when 
 mixed with the soil, ferments therein ; and by such fer- 
 ment dissolves, crumbles, and divides the earth very 
 much. This is the chief and almost only use of dung." 
 
INTRODUCTION 9 
 
 While underestimating the value of manure, he has 
 shown the importance of thorough tillage of the soil 
 more clearly than had ever been done before. " The 
 Horse-Hoeing Husbandry" by Jethro Tull is worthy 
 of careful study by all agricultural students. 
 
 During recent years the agricultural experiment 
 stations of this and other countries have made soils a 
 prominent feature of their work. Some of the results 
 obtained are noted in the following chapters. Our 
 knowledge regarding the chemistry, physics, geology, 
 and bacteriology of soils is still far from complete, 
 but many facts have been discovered which are of the 
 greatest value to the practical farmer. The literature 
 relating to soils and fertilizers has become very exten- 
 sive, and in the classification of agricultural subjects 
 for study, the soil forms one of the main divisions of 
 agronomy. 
 
 In soil investigations it has frequently happened, 
 owing to imperfect interpretation of results and to 
 the presence of many modifying influences, that the 
 conclusions of one investigator appear to be directly 
 contradictory to those of another. This is well illus- 
 trated in the investigations relating to the assimilation 
 of free atmospheric nitrogen, where seemingly opposite 
 conclusions now form a complete theory. 
 
 A scientific study of soils is valuable from an educa- 
 tional point of view, as well as because the practical 
 knowledge obtained can be utilized in the production 
 of crops. In the cultivation of soils, complicated physi- 
 
lO SOILS AND FERTILIZERS 
 
 cal, bacteriological, and chemical changes occur, many 
 of which are only imperfectly understood. The fun- 
 damental principles of soil fertility are, however, rea- 
 sonably well estabhshed, and it is now possible to 
 intelligently conserve the fertihty of soils and to pro- 
 duce maximum yields of crops. Since the soil wealth 
 is the greatest and the most important form of wealth 
 of a nation, intelligent effort should be made for its 
 conservation and development. 
 
CHAPTER I 
 PHYSICAL PROPERTIES OF SOILS 
 
 1. Soil. — Soil is that portion of the earth's crust 
 in which plants may grow. It is composed of pulver- 
 ized and disintegrated rock mixed with animal and 
 vegetable matter. The rock particles are of different 
 kinds and sizes, and are in various stages of decomposi- 
 tion. If two soils are produced from the same kind of 
 rock and differ only in the size of the particles, the 
 difference is merely a physical one. If, however, one 
 soil is formed largely from sandstone, while the other is 
 formed from granite, and the soil particles are not the 
 same in size, the difference is -both physical and chemi- 
 cal. Soils are derived from different kinds of rock 
 fragments, which are composed of minerals having 
 a different combination of elements and different per- 
 centage composition, and hence it is they differ both 
 physically and chemically. It is difficult to consider 
 the physical properties without also considering the 
 chemical properties. The chemical and physical prop- 
 erties, together, determine largely the agricultural value 
 of a soil. 
 
12 SOILS AND FERTILIZERS 
 
 2. Physical Properties Defined. — The physical prpp- 
 erties of a soil are : 
 
 1. Weight and volume. 
 
 2. Size, form, and arrangement of the soil particles. 
 
 3. The relation of the soil to air, water, heat, and 
 cold. 
 
 4. Color. 
 
 5. Odor and taste. 
 
 6. The relation of the soil to electricity. 
 
 3. Weight and Volume. — Soils vary in weight with the 
 composition and size of the particles. Fine sandy soils 
 weigh heaviest, while peaty soils are the lightest. 
 But when saturated with water, a cubic foot of peaty 
 soil weighs more than a cubic foot of sandy soil. A 
 given volume of clay soil weighs less than the same 
 volume of sandy soil. The larger the amount of or- 
 ganic matter, the less the weight. Pasture land, for 
 example, weighs less than arable land. A cubic foot 
 of soil from a field which has been well cultivated 
 weighs less than that from a field where the soil has 
 been compacted. Weight is an important property to 
 consider when the total amounts of plant food in two 
 soils are compared. A peaty soil containing i per cent 
 of nitrogen and weighing 30 pounds per cubic foot has 
 less total nitrogen than a soil containing 0.40 per cent 
 of nitrogen and weighing 80 pounds. 
 
 The weight of soils per cubic foot as determined from 
 apparent density is approximately as follows : ^ 
 
PHYSICAL PROPERTIES OF SOILS 1 3 
 
 Pounds 
 
 Clay soil .... 
 Fine sandy soil 
 Loam soil .... 
 Peaty soil .... 
 Average prairie soil 
 Uncultivated prairie soil 
 
 70 to 75 
 95 to no 
 75 to 90 
 25 to 40 
 
 75 
 
 65 
 
 It is estimated that an acre of soil to the depth of 
 one foot weighs in round numbers from 2,500,000 to 
 4,200,000 pounds, depending upon the chemical com- 
 position, size of soil particles, and state of compac- 
 tion. 
 
 The weight per cubic foot of soils in situ generally 
 exceeds the weight derived from the apparent density 
 of the dry soil ; this is because of the tendency of soils 
 in the field to become compacted. While a dry clay 
 soil reduced to a powder may show an apparent weight 
 of 70 pounds per cubic foot, the field weight (air-dry 
 basis) may range from 80 to 98 pounds, depending upon 
 the degree of compactness. 
 
 Between the soil particles are non-capillary or pore 
 spaces occupied by air or water. If the soil be con- 
 sidered a homogeneous mass without air spaces, it will 
 have an absolute specific gravity of about 2.6 ; with the 
 air spaces its apparent specific gravity is about 1.2. 
 That is, in its natural condition a soil weighs about 1.2 
 times heavier than the same volume of water. The 
 porosity of a soil is determined by dividing the apparent 
 
14 
 
 SOILS AND FERTILIZERS 
 
 by the real specific gravity.^ Ordinarily cultivated soils 
 have a pore space range from 30 to 60 per cent of the 
 volume of the soil, depending upon the conditions to 
 which the soil has been subjected. 
 
 4. Size of Soil Particles. — The size of soil particles 
 varies from those hardly distinguishable with the micro- 
 scope to coarse rock fragments and determines the type 
 of a soil as sand, clay, or loam. The term ' fine earth ' 
 is used to designate that part of a soil which passes 
 through a sieve with holes 0.5 mm. (0.02 inch) in di- 
 ameter. Coarse sand particles and rock fragments 
 which fail to pass through the sieve are called skeleton. 
 The amounts of fine earth and skeleton are variable. 
 Arable soils, in general, contain from 5 to 20 per cent 
 of skeleton. 
 
 The fine earth is composed of six grades of soil parti- 
 cles. The names and sizes are as follows : 
 
 Medium sand 
 Fine sand 
 Very fine sand 
 Silt . . ., 
 Fine silt . . 
 Clay . . . 
 
 Millimeters 
 
 0.5 to 0.25 
 0.25 to O.I 
 O.I to 0.05 
 0.05 to O.OI 
 o.oi to 0.005 
 0.005 ^"d less 
 
 Inches 
 
 0.02 to O.OI 
 O.OI to 0.004 
 0.004 to 0.002 
 0.002 to 0.OC04 
 0.0004 to 0.000; 
 0.0002 and less 
 
 Soils are mechanical mixtures of various-sized par- 
 ticles. In most soils there is a predominance of one 
 
PHYSICAL PROPERTIES OF SOILS 
 
 15 
 
 grade, as clay in heavy clay soils, and medium sand 
 in sandy soils. No soil, however, is composed entirely 
 of one grade. The clay particles are exceedingly 
 small ; it would take 5000 of the larger ones, if laid in 
 
 
 (p f^ t> 
 9 d -» 
 
 ' i , ^ " 
 
 a. <ii^ & ^ 
 
 
 
 ^ ^ i 
 ^ ^ 1 
 
 
 
 
 Fig. I. Medium sand x 150. Fig. 2. Fine sand x 150. FiG. 3. Very fine 
 sand X 150. Fig. 4. Silt x 325. Fig. 5. Fine silt x 325. FiG. 6. Clay x 325. 
 
 a line with the edges touching, to measure an inch, 
 while it would take but 50 of the medium sand par- 
 ticles to measure an inch. 
 
 5. Sand. — Sand is any rock fragment ranging in size 
 between 0.5 and 0.05 mm. in diameter. There are 
 
l6 SOILS AND FERTILIZERS 
 
 three grades, — fine, medium, and very fine. The chief 
 characteristic of sand is non-cohesion of particles. A 
 soil composed entirely of sand has little, if any, agri- 
 cultural value. Sandy soils usually contain from 5 
 to 15 per cent of clay and silt. The relative size of 
 sand, silt, and clay is shown in the illustration. In the 
 coarser grained sand, quartz predominates, while the 
 finer grained is composed mainly of other minerals. 
 
 6. Clay. — The term ' clay ' used physically denotes 
 those soil particles less than 0.005 ™rn- (0.0002 inch) 
 in diameter, without regard to chemical composition. 
 It may be silica, feldspar, limestone, mica, kaolin, or 
 any other rock or mineral which has been pulverized 
 until the particles are less than 0.005 i^im. in diameter. 
 Chemically, however, the term 'clay' is restricted to one 
 material, as explained in Section 74. The physical 
 properties of clay are well known. It has the power to 
 absorb large amounts of water, and will remain sus- 
 pended in water for a long time. The roiled appear- 
 ance of many streams and lakes is due to the presence 
 of suspended clay particles. The amount in agricul- 
 tural soils may range from 3 to 40 per cent. Clay 
 soils, if worked when too wet, become puddled; then 
 percolation cannot take place, and the accumulated 
 surface water must be removed by the slow process of 
 evaporation. As clays dry, they shrink, become tena- 
 cious, and are worked with difficulty. Clay soils owe 
 their properties to the fineness of division of the par- 
 
PHYSICAL PROPERTIES OF SOILS 1 7 
 
 tides rather than to their chemical composition. Any 
 mineral when finely pulverized has physical properties 
 similar to clay.'' 
 
 7. Silt. — Silt is composed of a great variety of rock 
 fragments. The particles are, in size, between sand 
 and clay. Chemical analysis shows them to be more 
 hydrated than the clay particles. Many of the western 
 prairie subsoils, clay-like in nature, are composed 
 mainly of silt, which imparts characteristics intermedi- 
 ate to sand and clay. While a clay soil is nearly im- 
 pervious to water, and when wet works with difficulty, a 
 silt soil is more permeable, but is not so open and 
 porous as a sandy soil. When a soil containing large 
 amounts of clay and silt is treated with water, the silt 
 settles slowly, while the clay remains in suspension. 
 The fine deposit in ditches and drains, where the 
 water moves slowly, is mainly silt. Soils composed 
 largely of silt deposited by water and mixed with vege- 
 table matter are among the most fertile. 
 
 8. Form of Soil Particles. — Soil particles are ex- 
 tremely varied in form. When examined with the 
 microscope they show the same diversity as is observed 
 among larger stones. In some soils the particles are 
 spherical, while in others they are angular. The shape 
 is determined by the way in which the soil has been 
 formed, and also by the nature of the rock from which 
 it was produced. 
 
1 8 SOILS AND FERTILIZERS 
 
 The form and arrangement of the particles are im- 
 portant factors to consider in deaHng with the water 
 content of soils. In the wheat lands of the Red River 
 Valley of the North, the particles are small and spher- 
 ical, being formed largely from limestone rock, while 
 the subsoil of the western prairie regions is composed 
 largely of angular silt particles, intermingled with clay, 
 forming a mass containing only a minimum of inter-soil 
 spaces. The silt particles being angular and embedded 
 in the clay, the soil has more the character of clay than 
 of silt. While these two soils are unlike in physical 
 composition, the form and arrangement of the particles 
 give each nearly the same water-holding power. Two 
 soils may have a somewhat similar mechanical composi- 
 tion and yet possess materially different physical proper- 
 ties because of a difference in the form and arrangement 
 of the soil particles. In some soils lo per cent of clay 
 is of more agricultural value than in other soils. Ten 
 per cent of clay associated with 60 or 70 per cent of 
 silt makes a good grain soil, while 10 per cent of clay 
 associated largely with sand makes a soil poorly suited 
 to grain culture. 
 
 The classification of the soil particles into clay, silt, 
 and fine, medium, and coarse sand is purely an arbitrary 
 one. Various authors use these terms in different ways, 
 and when comparing the mechanical composition of soils 
 reported in different works, one may avoid confusion 
 by omitting the names and noting only the sizes of the 
 particles. 
 
PHYSICAL PROPERTIES OF SOILS I9 
 
 9. Number of Particles per Gram of Soil. — It has 
 
 been estimated that a gram of productive soil contains 
 from 2,000,000,000 to 20,000,000,000 soil particles ; soils 
 which contain less than 1,700,000,000 are unproduc- 
 tive. The number of particles in a given volume of 
 soil varies with their size and form. According to 
 Whitney^ the number of particles per gram of differ- 
 ent soil types is as follows : 
 
 Early truck 1,955,000,000* 
 
 Truck and small fruit ...... 3,955,000,000 
 
 Tobacco 6,786,000,000 
 
 Wheat ........ 10,228,000,000 
 
 Grass and wheat 14,735,000,000 
 
 Limestone ........ 19,638,000,000 
 
 Assuming the particles are all spheres, it is es- 
 timated that in a cubic foot of soil a surface area of 
 from two to three and one half acres is presented to 
 the action of plant roots. 
 
 10. Method employed in Separating Soil Particles. — 
 
 Sieves with circular holes 0.5, 0.25, and o. i mm. are 
 employed for the purpose of separating the coarser 
 grades of sand. The sieve a, 0.5 mm, size, is connected 
 with the filtering flask c by means of the tube b, and the 
 flask is connected at point d with a suction pump. Ten 
 grams of soil, after soft pestling with boihng water, are 
 placed in the sieve and water is passed through until the 
 washings are clear. All particles larger than 0.5 mm. 
 * Figures below sixth place omitted and ciphers substituted. 
 
20 
 
 SOILS AND FERTILIZERS 
 
 remain in the sieve, and after drying and igniting, are 
 weighed. The contents of the flask c, containing the 
 particles less than 0.5 mm., are now passed through a 
 sieve having holes 0.25 mm. in diameter. 
 
 The fine sand and silt are separated by gravity. The 
 fine sand with some silt and clay are read- 
 ily deposited and the water containing the 
 suspended clay is decanted into a second 
 glass vessel. The residue is treated with 
 more water and allowed to settle, this opera- 
 tion being repeated until the microscope 
 shows the soil particles to be nearly all 
 of one grade. The separation of silt 
 and clay is facilitated 
 by the use of a centri- 
 fuge.^ 
 
 It is often difficult to fig. 8. 
 
 secure even an approximate separation of sand, silt, and 
 clay particles, because the finer particles tenaciously ad- 
 here to the larger ones. 
 
 The clay is obtained by evaporating an aliquot por- 
 tion of the washings or by determining the total per 
 cent of the other grades of particles and the volatile 
 matter and subtracting the sum from 100. This is the 
 modified Osborne sedimentation method.^'' 
 
 By means of Hilgard's elutriator^ a more extended sep- 
 aration of the soil particles is effected. For detailed direc- 
 tions for making mechanical analyses of soils the student 
 is referred to Wiley's " Agricultural Analysis," Vol. I. 
 
 Fig. 7. 
 
PHYSICAL PROPERTIES OF SOILS 
 
 21 
 
 SOIL TYPES 
 
 ll.\(Jrop Growth and Physical Properties. — The pref- 
 erence of certain crops for particular kinds of soil, as 
 wheat for a clay subsoil, potatoes for a sandy soil, and 
 corn for a silt soil, is due mainly to the characteristic of 
 the crop in requiring a definite amount of water, and a 
 certain temperature 
 for growth. These 
 conditions are met 
 by the soil being 
 composed of various 
 grades of particles 
 which enable a cer- 
 tain amount of water 
 to be retained, and 
 the soil to properly 
 respond to heat and 
 cold. In considering 
 soil types, it should 
 be remembered that 
 there are so many 
 conditions influenc- 
 ing crop growth that 
 the crop-producing 
 power cannot always be determined by a mechanical 
 analysis of the soil. The following types have been 
 found to hold true in a large number of cases under 
 average conditions, but they do not represent what 
 
 Fig. io. 
 
 First Centrifuge used in the Mechan- 
 ical Analysis of Soils. 
 
22 SOILS AND FERTILIZERS 
 
 might be true under special conditions. For example, 
 a sandy soil of good fertility in which the bottom water 
 is only a few feet from the surface, may produce larger 
 grain crops than a clay soil in which the bottom water 
 is at a greater depth. In judging the character of a 
 soil, the special conditions must always be taken into 
 consideration. In discussing the following soil types, a 
 normal supply of plant food and an average rainfall 
 are assumed in all cases. ^^ 
 
 12. Potato and Early Truck Soils. — The better types 
 of potato soils are those which contain about 60 per 
 cent of medium and fine sand, 30 per cent of silt, and 
 about 5 per cent of clay. Soils of this nature when 
 supplied with 3 per cent of organic matter will contain 
 from 10 to 20 per cent of water. The best conditions 
 for crop growth exist when the soil contains about 18 
 per cent of water. In a sandy soil, vegetation may 
 reduce the water to a much lower point than in a clay 
 soil, because the sandy soil gives up its water so readily 
 to growing crops and consequently a larger amount is 
 available, while on a heavy clay, crops show the want of 
 water when the soil contains from 10 to 12 per cent, 
 for the clay holds the water so tenaciously. When 
 potatoes are grown on soils where there is an abnormal 
 amount of water the crop is slow in maturing. For 
 early truck purposes in northern latitudes, sandy loam 
 soils are the most suitable because they warm up so 
 readily, and the absence of an abnormal amount of 
 
PHYSICAL PROPERTIES OF SOILS 23 
 
 water results in early maturity. Excellent crops of 
 potatoes are grown on many of the silt soils of the 
 west which have a materially different composition from 
 the type given. A soil may have all of the requisites 
 physically for the production of good potato and 
 truck crops, and still be unproductive on account of 
 unbalanced chemical composition or lack of plant 
 food. 
 
 13. General Truck and Fruit Soils. — For fruit grow- 
 ing and general truck purposes the soil should contain 
 more clay and less sand than for early truck farming. 
 Soils containing from lo to 15 per cent of clay and not 
 more than 50 per cent of sand are best suited for grow- 
 ing small fruits. Such soils will retain from 12 to 20 
 per cent of water. There is a noticeable difference in 
 the adaptability of different kinds of fruit to different 
 soils. Some thrive on clay land, provided the proper 
 cultivation and treatment are given. There is as much 
 diversity of soil required for producing different fruit 
 crops as for the production of different farm crops. As 
 a rule, however, a silt soil is most capable of being 
 adapted to the various conditions required by fruit 
 crops. 
 
 14, Corn Soils. — The strongest types of corn soils 
 are those which contain from 40 to 45 per cent of 
 medium and fine sand and about 15 per cent of clay. 
 Corn lands should contain 15 per cent of available 
 
24 SOILS AND FERTILIZERS 
 
 water. Heavy clays require more cultivation and pro- 
 duce corn which matures later than that grown on soil 
 not so close in texture. Many corn soils contain less 
 sand and clay, but more silt than the figures given. 
 If a soil has a high per cent of neutral organic matter, 
 good corn crops may be produced where there is less 
 than 12 per cent of clay. Soils with a high per cent 
 of sand are usually too deficient in available water to 
 produce a good crop of corn. On the other hand, 
 heavy clay soils are slow in warming up and thus are 
 not suited to corn culture. The western prairie soils, 
 which produce most of the corn raised in the United 
 States, are composed largely of silt. 
 
 The best types of corn soils have the necessary 
 mechanical composition for the production of good crops 
 of sorghum, cotton, flax, and sugar beets. However, 
 the amount of available plant food required for each of 
 these crops is not the same. 
 
 15. Medium Grass and Grain Soils. — For the produc- 
 tion of grass and grain a larger amount of water is 
 required than for corn. The yield is determined largely 
 by the amount of water which the soil contains. For 
 an average rainfall of 30 inches, a good grass and grain 
 soil should contain about 15 per cent of clay and 60 per 
 cent of silt. Such a soil ordinarily holds from 18 to 25 
 per cent of water. Many grass and grain soils have less 
 silt and more clay. A soil composed of about 30 per 
 cent each of fine sand, silt, and clay, is also suitable 
 
PHYSICAL PROPERTIES OF SOILS 
 
 25 
 
 mechanically, for general grain production. There are 
 a number of different types of grass and grain soils, 
 with different proportional amounts of sand, silt, and 
 
 Clay 
 
 f 
 
 I^^Pl 
 
 Fine ! 
 
 '•'''•'•'"•'■'••{'•':: 
 
 Silt 1 
 
 (I:--' :■.':'■ '-l'^ 
 
 Silt i 
 
 
 I 
 Very | 
 
 
 Fina -; 
 
 ^^^osScK 
 
 Sand L 
 
 ^^^ES*' 
 
 
 o«2oo'ooeoo 
 
 t^.. -m 
 
 
 Fig. ir. Soil Types. 
 
 I. Heavy wheat soil. 2. Average wheat soil. 3. Medium wheat and grain 
 
 soil. 4. Corn soil. 
 
 clay. Silt soils, however, form the largest part of the 
 grain soils of the United States. 
 
 16. Wheat Soils. — For wheat production, soils of 
 closer texture are required than for other small grains. 
 There are three classes of wheat soils. In the first 
 
26 SOILS AND FERTILIZERS 
 
 (i in Fig. ii) there are from 30 to 50 per cent of clay 
 particles, mostly disintegrated limestone. The soil of 
 the Red River Valley of the North belongs to this class. 
 The surface soil contains from 7 to 10 per cent of 
 vegetable matter and the subsoil about 25 per cent of 
 limestone in a very fine state of division. For the pro- 
 duction of wheat, the subsoil should have a good store 
 of water. 
 
 The second type of wheat soil (2 in Fig. 11) has less 
 clay and more silt. Many prairie subsoils which pro- 
 duce good crops of wheat contain about 25 per cent of 
 sand, 50 per cent of silt, and from 18 to 25 per cent of 
 clay. Soils of this class when well stocked with moisture 
 in the spring produce good crops of wheat, but are not 
 able to withstand drought so well as soils of the first 
 class ; during wet seasons, however, the yields are larger 
 than on heavier clay soils. 
 
 To the third class of wheat soils (3 in Fig. 11) belong 
 those which are composed mainly of silt, containing 
 usually 75 per cent, and from 10 to 15 per cent of 
 clay. The high per cent of fine silt gives the soil clay- 
 like properties. Soils of this class are adapted to a 
 great variety of crops. For the production of wheat it 
 is essential that a good supply of organic matter be 
 maintained in such soils so as to bind together the soil 
 particles. The special peculiarities of the different 
 grain crops as to soil requirements are discussed in 
 connection with the food of crops. 
 
PHYSICAL PROPERTIES OF SOILS 
 
 27 
 
 Mechanical Composition of Soil Types ^ 
 
 Kind of Soil 
 
 Heavy 
 Wheat 
 
 Medium 
 Wheat 
 
 Grass 
 
 and 
 
 Grain 
 
 Corn 
 
 Potato, 
 
 ETC. 
 
 Name of Particles 
 
 Size in Millim. 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 Medium sand 
 
 0.5 to 0.25 
 
 
 3.18 
 
 1.20 
 
 24.60 
 
 59.04 
 
 Fine and very 
 
 
 
 
 
 
 
 fine sand 
 
 0.25 to 0.05 
 
 6.18 
 
 21.43 
 
 4.14 
 
 21.51 
 
 5.60 
 
 Silt 
 
 0.05 to O.OI 
 
 20.25 
 
 27.75 
 
 44-35 
 
 11.08 
 
 9.07 
 
 Fine silt 
 
 o.oi to 0.005 
 
 IO-35 
 
 17.60 
 
 3075 
 
 12.81 
 
 19-33 
 
 Clay 
 
 0.005 
 
 57.00 
 
 25.00 
 
 15-45 
 
 22.80 
 
 4.05 
 
 Total volatile 
 
 
 6.22 
 
 5.04 
 
 4.11 
 
 7.20 
 
 2.91 
 
 1. A heavy wheat soil from the Red River Valley, — the clay 
 consists largely of disintegrated limestone. 
 
 2. Medium wheat soil from Western Minnesota. 
 
 3. A loam soil adapted to grasses and grains. From Minnesota 
 Experiment Station. 
 
 4. A corn soil from Southwestern Minnesota. 
 
 5. A potato soil from Eastern Minnesota. 
 
 17. Sandy, Clay, and Loam Soils. — Ordinarily in 
 agricultural literature, the term 'sandy,' 'clay,' or 'loam' 
 is used to designate the prevaihng character of a 
 soil. Sandy soils usually contain 90 per cent or more 
 of silica or chemically pure sand. The term ' light 
 sandy soil ' is sometimes used to indicate that the 
 soil is easily worked, while ' heavy clay ' means that 
 the soil offers great resistance to cultivation. Many 
 soils which are clay-like in character are not composed 
 
28 
 
 SOILS AND FERTILIZERS 
 
 very largely of clay. There are subsoils in the western 
 states which have clay-like characteristics but contain 
 only about 15 per cent of clay, the larger part of the 
 soil being silt. A loam soil is a mixture of sand and 
 clay ; if clay predominates, it is a clay loam, while if 
 sand predominates, it is a sandy loam. 
 
 RELATION OF THE SOIL TO WATER AND AIR 
 
 18. Amount of Water required by Crops. — Experi- 
 ments show that it takes from 275 to 375 pounds of 
 water to produce a pound of dry matter in a grain crop. 
 In order to produce an acre of average wheat, 350 tons 
 of water are needed. The amount of water required 
 for the production of an acre of various crops is as 
 follows : ^^ 
 
 Clover . 
 Potatoes 
 Wheat . . 
 Oats . . . 
 Peas 
 
 Corn . . . 
 Grapes . 
 Sunflowers" 
 
 Average Amount 
 Tons Water 
 
 400 
 400 
 
 375 
 375 
 300 
 
 375 
 6000 
 
 Minimum Amount 
 Tons Water 
 
 310 
 
 325 
 300 
 300 
 300 
 
 The amount of water required for the production of 
 crops in humid and arid regions has not been exten- 
 
PHYSICAL PROPERTIES OF SOILS 29 
 
 sively investigated. Ordinarily crop yield is directly 
 proportional to and dependent upon the water supply. 
 The rainfall during the time of growth is frequently 
 less than the amount of water required for the produc- 
 tion of the crop. One inch of rainfall is equal to about 
 112 tons of water per acre. An average of two inches 
 per month during the three months of crop growth is 
 equivalent to only 675 tons, a large part of which is lost 
 by surface drainage and by evaporation. Hence it is 
 that the rainfall during an average growing season is 
 less than the amount of water required to produce 
 crops, and consequently the water stored up in the 
 subsoil must be drawn upon to a considerable extent. 
 Inasmuch as the soil's reserve supply of water is such 
 an important factor in crop production, it follows that 
 the capacity of the subsoil for storing up and supplying 
 water as needed is a matter of much importance, par- 
 ticularly since the power of the soil for absorbing and 
 retaining water may be influenced by cultivation and 
 manuring. Before discussing the influence of cultiva- 
 tion upon the soil water, the forms in which water is 
 in the soil should be studied. It is present in three 
 forms: (i) bottom water, (2) capillary water, and (3) 
 hydroscopic water. 
 
 19. Bottom Water is that which stands in the soil at 
 a general level, and fills all the spaces between the soil 
 particles. Its distance from the surface can be told in 
 a general way by the depth of surface wells. Bottom 
 
30 SOILS AND FERTILIZERS 
 
 water is of service to growing crops when it is at such 
 a depth that it can be brought to the plant roots by 
 capillarity, but when too near the surface, so that the 
 roots are immersed, the conditions are unfavorable for 
 crop growth. When the bottom water can be brought 
 within reach of the roots by capillarity, a crop has an 
 almost inexhaustible supply. In many soils known as 
 old lake bottoms, such a condition exists. 
 
 20. Capillary Water. — The water held in the minute 
 spaces above the bottom water is known as the capillary 
 
 water. The capillary spaces 
 of the soil are the small spaces 
 between the soil particles in 
 which water is held by surface 
 tension, the force acting be- 
 tween the soil and the water 
 Fig. 12. Water Film surrounding being greater than the force 
 Soil Particles. q£ gj-^vity. If a scrics of glass 
 
 tubes of different diameters be placed in water, it will be 
 observed that in the smaller tubes water rises much 
 higher than in the larger. The water rises in all of 
 the tubes until a point is reached where the force of 
 gravity is equal to the force of surface tension. In 
 the smaller tubes surface tension is greater than the 
 force of gravity, and the water is drawn up into the 
 tube inversely proportional to its diameter. In the 
 larger tubes the surface tension is less and the water 
 is raised only a short distance. There are present in the 
 
PHYSICAL PROPERTIES OF SOILS 
 
 31 
 
 soil many spaces which are capable of taking up water 
 in the same way. The height to which water can be 
 raised by capillarity de- 
 pends upon the size and 
 arrangement of the soil 
 particles, it may be to a 
 height of several feet. 
 Ordinarily, however, the 
 capillary action of water 
 is confined to a few feet. 
 The arrangement of the 
 soil particles influences 
 greatly the capillary power 
 of a soil. Usually from 
 30 to 60 per cent of the 
 bulk of a soil is air space ; 
 by compacting, the air 
 spaces are decreased ; by 
 stirring, they are increased. 
 In soils of close texture, 
 as heavy clays, an increase 
 in air spaces results in an 
 increase of capillary spaces 
 
 Fig. 13. Showing Rise of Water in 
 Capillary and other Tubes. 
 
 and of water-holding capacity, while in other soils, as 
 coarse sandy soils, increasing the air spaces decreases 
 the capillary spaces and the water-holding capacity. 
 The best conditions for crop production exist when the 
 soil contains water to the extent of about 40 per cent 
 of its total capacity for saturation. 
 
32 SOILS AND FERTILIZERS 
 
 21. Hydroscopic Water. — By hydroscopic water is 
 meant the water that is held mechanically in the soil 
 and is not removed by air drying. The air which 
 occupies the non-capillary spaces of the soil is charged 
 with moisture in proportion to the water in the soil. 
 Under normal conditions the soil atmosphere is nearly 
 saturated. When soils have exhausted their capillary 
 water, the water in the soil atmosphere is correspond- 
 ingly reduced. The available supply in other forms 
 being exhausted, the hydroscopic, water cannot con- 
 tribute to plant growth unless supplemented by heavy 
 fogs. 
 
 22. Loss of Water by Percolation. — Whenever a 
 soil becomes saturated, percolation or a downward 
 movement of the water begins. The extent to which 
 losses by percolation may occur depends upon the 
 character of the soil and the amount of rainfall. 
 When soils are covered with vegetation, the losses 
 are less than from barren fields. In all soils which 
 have only a limited number of capillary spaces and a 
 large number of non-capillary spaces, the amount of 
 water which can be held above the bottom water is 
 small. From such soils the losses by percolation are 
 greater than from soils which have a larger number 
 of capillary spaces, and a smaller number of non-capil- 
 lary spaces. In coarse sandy soils many of the spaces 
 are too large to be capillary. 
 
 If all of the water which falls on some soils could 
 
PHYSICAL PROPERTIES OF SOILS 33 
 
 be retained and not carried beyond the reach of crops 
 by percolation, there would be an ample supply for 
 agricultural purposes. The texture of the soil may be 
 changed by cultivation and by the use of manures so 
 as to prevent losses by percolation. If the soil is of 
 very fine texture, as a heavy clay, percolation is slow, 
 and before the water has time to sink into the soil, 
 evaporation takes place. With good cultivation, the 
 water is able to penetrate to a depth beyond the im- 
 mediate influence of evaporation. Compacting an open 
 porous soil by rolling, checks rapid percolation and pre- 
 vents the water from being carried beyond the reach of 
 plant roots. Thus it will be seen that the treatment 
 necessary to prevent excessive losses by percolation, 
 varies with different soils. In regions of heavy rain- 
 fall and mild winters the losses of both water and plant 
 food by percolation are often large, 
 
 23. Loss of Water by Evaporation, — The factors 
 which influence evaporation are temperature, humidity, 
 and rate of movement of the air. When the air con- 
 tains but little moisture and is heated and moving 
 rapidly, the most favorable conditions for evaporation 
 exist. In semi-arid regions the losses of water by 
 evaporation are much greater than by percolation. 
 The dry air comes in contact with the soil, the soil 
 atmosphere gives up its water taken from the soil, 
 and, unless checked by cultivation, the subsoil water is 
 brought to the surface by capillarity and lost. In porous 
 
 D 
 
34 SOILS AND FERTILIZERS 
 
 soils a greater freedom of movement of the air is possi- 
 ble, which increases the rate of evaporation. When the 
 surface of the soil is covered with a layer of finely pul- 
 verized earth, or with a mulch, excessive losses by 
 evaporation cannot take place, because a material of 
 different texture is interposed between the soil and the 
 air. 
 
 24. Loss of Water by Transpiration. — Losses of 
 water may also occur from the leaves of plants by 
 the process known as transpiration. Helriegel ob- 
 served that during some years lOO pounds more water 
 were required to produce a pound of dry matter than in 
 other years, because of the difference in the amount of 
 water lost in this way. The loss of water by evapora- 
 tion can be controlled by cultivation, but the loss by 
 transpiration can be only indirectly influenced. Hot, 
 dry winds may cause crops to wilt because the water 
 lost by transpiration exceeds the amount which the 
 plant takes from the soil. 
 
 25. Drainage. — Good drainage is essential in order 
 to properly regulate the water supply. An excess of 
 water in the soil is equally as injurious as a scant 
 amount. If the water which falls on the land is allowed 
 to flow over the surface and is not retained in the soil, 
 there is not sufficient reserve water for crop growth. 
 The object of good drainage is to store as much water 
 as possible in the subsoil and prevent surface accumu- 
 
PHYSICAL PROPERTIES OF SOILS 35 
 
 lation and loss. Good drainage is accomplished by 
 thorough cultivation, and in regions of heavy rainfall, 
 by tile drainage. Well-drained land is warmer in the 
 spring, has a larger reserve store of water, and is in 
 better condition for crop growth. Many swampy lands 
 are highly productive when properly drained. A high 
 state of productiveness cannot be maintained without 
 suitable provision for drainage. When the pores of the 
 soil are filled with water, air is excluded and the neces- 
 sary chemical and bacteriological changes which result 
 in rendering plant food available fail to take place. The 
 drainage of wet and low lands forms an important fea- 
 ture of rural engineering. 
 
 26. Influence of Forest Regions. — The deforesting of 
 large areas near the sources of rivers has an injurious 
 influence upon the moisture content of adjoining farm 
 lands. By cutting over and leaving barren large tracts, 
 less water is retained in the soil. Also near forests the 
 air has a higher moisture content, due to the water given 
 off by evaporation. Lands adjacent to deforested dis- 
 tricts lose water more rapidly by evaporation, because 
 the air is so much drier. In Section 24 it is stated that 
 losses of water by transpiration can be indirectly influ- 
 enced. This can be accomplished by retaining the 
 forests. 
 
 Good drainage is necessary not only for individual 
 farms, but also for an entire community. Good storage 
 capacity in the form of forest lands, for the surplus 
 
36 SOILS AND FERTILIZERS 
 
 water which accumulates near the sources of large 
 rivers is also a necessity to agriculture. 
 
 The three ways by which crops are deprived of water 
 are, — (i) percolation, (2) evaporation, and (3) transpira- 
 tion. With proper methods of cultivation losses by per- 
 colation and evaporation may be controlled, and losses 
 by transpiration may be reduced. 
 
 INFLUENCE OF CULTIVATION UPON THE WATER 
 SUPPLY OF CROPS 
 
 27. Capillarity influenced by Cultivation. — The capil- 
 larity and moisture content of soils can be influenced by 
 __ different methods of 
 
 "^"^-^S^^^^^^,^^ cultivation, as rolling 
 
 and subsoiling, deep 
 plowing, and shallow 
 surface cultivation. 
 lilllilllUliJilliiiiJilliJiliJIIillllllliiyi!::^^ uJi^iM^^ Xhe treatment which 
 
 FIG. 15. Soil with Surface Cultivation. ^ ^^-j ^^^^^^^ rCCCive 
 
 in order to insure the best water supply for crops must 
 vary with the rainfall, the nature of the soil, and the 
 crop to be produced. It frequently happens that the 
 annual rainfall is sufficient to produce good crops, but it 
 is too unevenly distributed, and hence is not all utilized 
 to the best advantage. Losses of water occur through 
 surface drainage, percolation, and excessive evaporation, 
 but if it were properly stored in the subsoil and conserved 
 by cultivation, these losses would be prevented and there 
 would be sufficient for crop production. 
 
PHYSICAL PROPERTIES OF SOILS 37 
 
 It is possible, to a great extent, to vary the cultiva- 
 tion so as to conserve the moisture of the soil to meet 
 the requirements of crops. 
 
 28. Shallow Surface Cultivation. — When shallow sur- 
 face cultivation is practiced, the capillary spaces near 
 the surface are destroyed and the direct connection of 
 the subsoil water with 
 
 l||iiiii,iilllFlllJliii|lll.lfi|ftiitii 
 
 the upper layer is If 
 broken, the ground is 
 covered with finely 
 
 pulverized earth, and ^^' ■ — — — ——^-^.^ \ j 
 
 the soil particles have ^'^- ^^- s°'' ^■''^^°"* ^""^^^^ Cultivation. 
 been disturbed so there is not that close contact which 
 enables the water to pass from particle to particle. When 
 evaporation takes place there is a movement of the sub- 
 soil water to the surface, but if that is covered with a 
 layer of fine earth, the subsoil water cannot readily pass 
 through such a medium, and evaporation is checked. 
 Hence shallow surface cultivation conserves the soil 
 moisture. 
 
 The means bv which surface cultivation is accom- 
 plished must, of necessity, vary with the nature of the 
 soil. If a harrow is used, the pulverization should be 
 complete, if a disk, the teeth should be set at an angle, 
 and not perpendicularly, so as to prevent, as suggested 
 by King,^^ the formation of hard ridges which hasten 
 evaporation. When the disk is set at an angle, a layer 
 of soil is completely cut off, and the capillary connec- 
 
38 
 
 SOILS AND FERTILIZERS 
 
 tion with the subsoil is broken. Surface cultivation 
 should be from two to three inches deep, and the finer 
 the condition in which the surface soil is left, the better. 
 Shallow surface cultivation does not mean that the soil 
 should not be previously well prepared by thorough cul- 
 tivation. It can be practiced in connection with deep 
 plowing, shallow plowing, subsoiling, or rolling ; in fact, 
 it can be combined with any method of treating the 
 land, and is an effectual means of conserving soil mois- 
 ture. The following example shows the extent to which 
 shallow surface cultivation may conserve the soil water : ^^ 
 
 
 
 Per Cent of Water in Cornfield 
 
 
 With shallow surface 
 cultivation 
 
 Without shallow surface 
 cultivation 
 
 Soil, depth 3 to 9 inches 
 Soil, depth 9 to 15 inches 
 
 14.12 
 17.21 
 
 8.02 
 12.38 
 
 29. Cultivation after a Rain. — When evaporation 
 takes place immediately after a rain, not only is there 
 a loss of the water which has fallen, but there may 
 also be a loss of the subsoil water by translocation, if 
 nothing be done to prevent.^^ After a rain, soils should 
 be cultivated as soon as the implements will work well, 
 so as to check evaporation and prevent the formation 
 of a crust. The following example shows the extent 
 to which the subsoil water may be brought to the 
 surface : ^* 
 
PHYSICAL PROPERTIES OF SOILS 
 
 39 
 
 
 Per Cent of W;»ter 
 
 
 Surface soil. 
 I to 3 inches 
 
 Subsoil, 
 6 to 12 inches 
 
 Before the shower 
 
 After the shower 
 
 9-77 
 
 22.11 
 
 18.22 
 16.70 
 
 The rainfall was sufficient to have raised the water 
 content of the surface soil to 20.77 P^r cent. The sub- 
 soil showed a loss of 1.52 per cent, while the surface 
 soil showed a gain of 1.34 per cent in addition to the 
 water received from the shower. If evaporation begins 
 before the equilibrium is reestablished, there is lost, not 
 only the water from the shower, but also the water 
 which has been translocated from the subsoil to the 
 surface. Hence the importance of shallow surface 
 cultivation immediately after a rain. 
 
 When the subsoil contains a liberal supply of water, 
 and the surface soil a minimum amount, there is after a 
 shower a movement of the subsoil water to the surface. 
 The soil particles at the surface are surrounded with 
 films of water which thicken at the expense of the sub- 
 soil water. Surface tension is the cause of this movement 
 of the water to the surface, and under the conditions 
 stated it is temporarily greater than the force of gravity. 
 
 A hard, thin crust should never be allowed to form 
 after a rain, because it hastens losses by evaporation, 
 while a soil mulch formed by surface cultivation has the 
 opposite effect. 
 
40 SOILS AND FERTILIZERS 
 
 30. Rolling. — The use of heavy rollers for compact- 
 ing the soil is beneficial in a dry season on a soil con- 
 taining large proportions of sand and silt. Rolling 
 compacts the land and improves the capillary condi- 
 tion, enabhng more of the subsoil water to be brought 
 to the surface. Experiments show that when land is 
 rolled the amount of water in the surface soil is in- 
 creased. This increase is, however, at the expense of 
 the subsoil water.^^ Unless rolled land receives surface 
 cultivation, excessive losses by evaporation, due to im- 
 proved capillarity, may result. The use of the roller on 
 heavy clay during a wet season results unfavorably. 
 Occasionally, Hght rolling of clay land is beneficial in 
 pulverizing the clods. 
 
 In some localities rolling and subsequent surface cul- 
 tivation are not admissible on account of drifting of the 
 soil, caused by heavy winds. 
 
 31. Subsoiling. — By subsoiling is meant pulverizing 
 the soil below the furrow slice. This is accompUshed 
 with the subsoil plow, which simply loosens without 
 bringing the subsoil to the surface. The object of sub- 
 soiling is to enable the land to retain, near the surface, 
 more of the rainfall. Heavy clay lands are sometimes 
 improved by occasional subsoiling, but its continued 
 practice is not desirable. For orcharding and fruit 
 growing, it is frequently resorted to, but is not bene- 
 ficial on soils containing large amounts of sand and silt. 
 Rolling and subsoiling are directly opposite in effect. 
 
PHYSICAL PROPERTIES OF SOILS 4 1 
 
 Soils which are improved by rolling are not improved 
 by subsoiling. The additional expense involved should 
 be considered when subsoiling is to be resorted to. Ex- 
 periments have not as yet been sufficiently decisive to indi- 
 cate all of the conditions most favorable for this practice. 
 
 32. Fall Plowing followed by surface cultivation con- 
 serves the soil water, by checking evaporation and leav- 
 ing the land in better condition to retain moisture. If 
 conditions allow, fall plowing can be followed by surface 
 cultivation, but in some localities heavy winds prevent 
 this. It is generally better to give the surface cultiva- 
 tion early the following spring. Clay land should be 
 left in a ridged condition when fall plowed, so as to ex- 
 pose a greater surface area and to allow a better oppor- 
 tunity for the water to sink into the subsoil. Evaporation 
 may take place from unplowed land during the fall, and 
 in the spring the soil contain appreciably less water than 
 plowed land. By fall plowing it is possible to carry over 
 a water balance of lOO tons or more from one year to 
 the next. 
 
 33. Spring Plowing. — When land is plowed late in 
 the spring there has been a loss of water by evapora- 
 tion, and the soil has not been able to store up as much 
 of the rain and snow as if fall plowing had been prac- 
 ticed.^^ Then, too, dry soil is plowed under and moist 
 soil brought to the surface, and if surface cultivation does 
 not follow, this moisture is readily lost by evaporation, 
 
42 
 
 SOILS AND FERTILIZERS 
 
 good capillary connection of the surface soil and subsoil 
 is not obtained, and the furrow slice soon becomes dry. 
 
 
 Per Cent of Water in" 
 
 
 Fall-plowed 
 land 
 
 Spring-plowed 
 land 
 
 From 2 to 6 inches 
 
 From 6 to I2 inches 
 
 From 12 to 1 8 inches 
 
 247 
 26.6 
 28.8 
 
 22.4 
 24.1 
 26.5 
 
 Average difference 
 
 2.37 per cent 
 
 Surface cultivation should immediately follow spring 
 plowing. 
 
 34. Mulching. — The use of well-rotted manure or 
 straw, spread over the surface as a mulch, prevents 
 evaporation. In forests the leaves form a mulch which 
 is an important factor in maintaining the water supply. 
 In order that a mulch be effectual, it must be com- 
 pacted, — a loose pile of straw is not a mulch. In 
 reclaiming lands gullied by water, mulching is very 
 beneficial, also a light mulch may be used to encourage the 
 growth of grass on a refractory hillside. Surface cultiva- 
 tion and mulching may be advantageously combined.^* 
 
 
 Per Cent of Water in 
 
 
 Mulched straw- 
 berry patch 
 
 Unmulched 
 
 Soil 2 to 5 inches 
 
 Soil 6 to 12 inches 
 
 Soil 12 to 18 inches 
 
 18.12 
 22.18 
 24.31 
 
 II. 17 
 18.14 
 21. II 
 
PHYSICAL PROPERTIES OF SOILS 43 
 
 35. Depth of Plowing. — The depth to which a soil 
 should be plowed in order to give the best results must, 
 of necessity, vary with the conditions. Deep plowing 
 of sandy land is not advisable, particularly in the spring. 
 On clay land deeper plowing should be the rule. The 
 longer a soil is cultivated, the deeper and more thorough 
 should be the cultivation. While shallow plowing is 
 admissible on new prairie land, deeper cultivation 
 should be practiced when the land has been cropped 
 for a series of years. Also, the depth of plowing should 
 be regulated by the season. In prairie regions, and in 
 the northwestern part of the United States, shallow 
 plowing is more generally practiced than in the eastern 
 states. Deep plowing in the fall gives better results 
 than in the spring. It is not a wise plan to plow to the 
 same depth every year. Professor Roberts says : ^^ " If 
 plowing is continued at one depth for several seasons, 
 the pressure of the implement and the trampling of the 
 horses in time solidify the bottom of the furrow, but if 
 the plowing is shallow in the spring and deep in sum- 
 mer and fall, the objectionable hardpan will be largely 
 prevented." 
 
 In regions of scant rainfall deep plowing of silt 
 soils should be done only at intervals of three or 
 five years, but with an average rainfall, deep plowing 
 should be the rule on soils of close texture. The 
 depth of plowing should be varied to meet the re- 
 quirements of the crop and soil and the amount of 
 rainfall. 
 
44 
 
 SOILS AND FERTILIZERS 
 
 36. Permeability of Soils. — The rapidity with which 
 water sinks into the soil after a rain depends upon 
 the nature of the soil, and the cultivation which it has 
 received. Shallow surface cultivation leaves the soil in 
 good condition to absorb water. When the surface is hard 
 and dry a large per cent of the water which falls on roll- 
 ing land is lost by surface drainage. Soils of close tex- 
 ture, which contain but few non-capillary spaces, offer the 
 greatest resistance to the downward movement of water. 
 A soil is permeable when it is of such a texture that 
 
 it does not allow the 
 water to accumulate 
 and clog the non-capil- 
 lary spaces. Cultiva- 
 tion may change the 
 tilth of even a clay soil 
 to such an extent as to 
 render it permeable. 
 Deep plowing increases 
 permeability. In regions of heavy rains, increased 
 permeability is very desirable for good crop production 
 on heavy clays. Sandy and loamy soils have naturally 
 a high degree of permeability, and it is not necessary 
 that it should be increased. 
 
 Fig. 17. Sandy Soil without Manure. 
 
 37. Fertilizers. — When water contains dissolved 
 salts, it is more susceptible to the influence of surface 
 tension, and is more readily brought to the surface of the 
 soil. In commercial fertilizers soluble salts are present. 
 
PHYSICAL PROPERTIES OF SOILS 
 
 45 
 
 However, the beneficial effect of these upon the moisture 
 content of soils is liable to be overestimated, because 
 the fertilizer undergoes fixation when applied, and does 
 not remain in a soluble condition. Fertilizers containing 
 soluble salts exercise a favorable influence upon the 
 moisture content of soils, but the extent of this influence 
 has never been determined under field conditions. 
 
 38. Farm Manures. — Farm manures exercise a bene- 
 ficial effect upon the moisture content of soils. When 
 the manure is worked into a soil, the coarse soil particles 
 
 and masses bind ^^.^Eiar*-"*-^ -v-.jm^ 
 
 together, and the ^<*r.,:i!lilP' >>"■» »a*^r^^' 
 
 non-cap il lar y 
 spaces are made 
 capillary. Free 
 circulation of the 
 air, which in- 
 creases evapora- 
 tion, is prevented 
 when a sandy soil is manured. When soils are manured 
 they retain more water, as shown by the following 
 example : ^^ 
 
 Fig. i8. Sandy Soil with Manure. 
 
 
 
 95 PER Cent Fine 
 
 
 Fine Sandy 
 
 Sandy Soil 
 
 
 Soil. 
 
 AND 5 PER 
 
 
 Per Cent 
 
 Cent Manure. 
 Per Cent 
 
 Capacity for holding water .... 
 
 25 
 
 42 
 
46 
 
 SOILS AND FERTILIZERS 
 
 The manure enables the soil to retain more of the 
 moisture near the surface and prevents losses by perco- 
 lation. The difference in moisture content between 
 manured and unmanured land is particularly noticeable 
 in a dry season.^* 
 
 Soil I to 6 inches 
 
 Sandy Soil 
 
 WELL Manured. 
 
 Water 
 
 Per Cent 
 10.50 
 
 Sandy Soil 
 
 Unmanured. 
 
 Water 
 
 Per Cent 
 8.10 
 
 Coarse leached manure may have just the opposite 
 effect by producing an open and porous condition of the 
 soil. 
 
 RELATION OF SOIL TO HEAT 
 
 39. Soil Temperature. — The way in which a soil 
 responds to heat and cold is an important factor in its 
 crop-producing value. A soil temperature of 42° to 
 50° F. is required for crop growth, and the best condi- 
 tions do not exist until the soil has reached a tempera- 
 ture of 60° to 70° F. During cold springs in northern 
 latitudes the soil is often so cold as to retard the germi- 
 nation process, and to affect the vitality of seeds, caus- 
 ing a poor stand of grain. 
 
 40. Heat required for Evaporation. — It is estimated 
 that the heat required to evaporate a pound of water at 
 60° F. would raise the temperature of 1000 pounds of 
 water 1° F. When water evaporates, the soil is 
 
PHYSICAL PROPERTIES OF SOILS 47 
 
 cooled, and if the heat for evaporation is all furnished 
 by the surrounding soil, it materially lowers the soil's 
 temperature and unfavorably affects crop growth. In 
 the early spring, drying winds may temporarily lower 
 the soil temperature by hastening evaporation. Much 
 heat is unnecessarily lost in evaporating excessive 
 amounts of water which should be removed by good 
 systems of drainage. 
 
 41. Temperature of Drained and Undrained Land. — 
 
 The surface of well-drained land is usually several 
 degrees warmer than that of poorly drained land. Water 
 being a poor conductor of heat, it follows that soils 
 which are saturated are slow to warm up in the spring. 
 At a depth of 2 or 3 feet the difference in tempera- 
 ture between wet and dry soils is not marked. It is to 
 be observed that with proper systems of drainage the 
 surplus water is removed from the surface soil and 
 stored up in the subsoil for future use by the crop, and 
 at the same time the temperature of the surface soil is 
 raised, thus improving the conditions for growth. The 
 relation of drainage to the temperature and proper 
 supply of water for crop growth, receives too little con- 
 sideration in field practice. When the land is well 
 drained, and receives early cultivation, the conditions 
 are best. 
 
 42. Color of Soils and Absorption of Heat. — All dark- 
 colored soils have greater power of absorbing heat 
 
48 SOILS AND FERTILIZERS 
 
 than those light in color. Schiibler observed a differ- 
 ence in temperature of 8° C. between the same soils, 
 when given a white coating with magnesia and a black 
 coating with lampblack.^'^ Black humus soils usually 
 contain so much water that the additional heat is utilized 
 for evaporation, and this results in the soil being cooler 
 than light-colored sandy soil. 
 
 43. Specific Heat of Soils. — Soils have a low specific 
 heat ; it requires only about one fifth as much to raise a 
 pound of soil i° as is required to raise a pound of water 
 1°. When soils are wet, the specific heat is greatly 
 increased, and they respond more slowly to the influ- 
 ence of the sun's rays. Sand has the lowest specific 
 heat of any soil constituent and retains the least water, 
 hence sandy soils warm up more readily than other soils. 
 On the other hand, clay soils, although slower to warm 
 up in the spring, retain their heat longer. 
 
 44. Farm Manures and Soil Temperature. — When the 
 animal and vegetable matter of the soil decays, heat is 
 produced. The slow oxidation of manure in the soil 
 yields in the end as much heat as if the dry manure 
 were burned. Whenever combustion or oxidation takes 
 place, heat results. 
 
 Manured land is usually i° or 2° warmer in the spring 
 than unmanured land. It has been estimated that the 
 amount of organic matter which undergoes oxidation in 
 an acre of rich prairie soil produces as much heat 
 
PHYSICAL PROPERTIES OF SOILS 49 
 
 annually as the burning of a ton of coal.^ The addi- 
 tional heat in well-drained and well-manured land is an 
 important factor in stimulating crop growth, particu- 
 larly in a cold backward spring. The production of 
 heat from manure is utilized in the case of hotbeds 
 where manure in rotting raises the temperature of the 
 soil. When soils are well manured, heat is retained 
 more effectually and crops on such land often escape 
 early frosts. 
 
 45. Influence of Exposure upon Soil Temperature. — 
 
 Land with a southern slope receives the sun's rays 
 longer and at a better angle for absorbing heat than 
 land sloping to the north. In valleys and low places 
 the soil at night cools more rapidly than on higher 
 ground, and hence crops in valleys may be injured by 
 late spring and early autumn frosts, while those on 
 higher and warmer land escape. 
 
 46. Influence of Cultivation upon Soil Temperature. — 
 
 Thorough cultivation resulting in the production of a 
 fine pulverized seed bed enables the soil to absorb a 
 larger amount of heat than if left in a rough lumpy con- 
 dition. Cultivated land is more porous and allows 
 greater freedom of movement of water into the subsoil. 
 Warm spring rains have a marked effect upon the 
 temperature of cultivated soils by filling the pores with 
 warm water. The influence of temperature upon nitri- 
 fication is discussed in Chapter IV. 
 
50 SOILS AND FERTILIZERS 
 
 47. Relation of Heat to Crop Growth. — All plant life 
 is directly dependent upon solar heat as the source of 
 energy for the production of plant tissue. The heat of 
 the sun is the main force at the plant's disposal for 
 decomposing water and carbon dioxide and for produc- 
 ing starch, cellulose, and other compounds. The growth 
 of crops is the result of the transformation of solar heat 
 into chemical energy which is stored up in the plant. 
 When the plant is used for fuel or for food, the quantity 
 of heat produced by complete oxidation is equal to the 
 amount required for the formation of the plant's tissue. 
 
 48. Color of Soils. — The principal materials which 
 impart color to soils are organic and iron compounds. 
 A union of the decaying organic matter (humus) with 
 the minerals of the soil produces compounds brown or 
 black in color, and consequently soils containing large 
 amounts of humus are dark-colored. When moist, soils 
 are darker than when dry, and soils in which the organic 
 matter has been kept up by the use of manures are 
 darker than unmanured soils.^^ When rich, black, prai- 
 rie soils lose their organic matter through injudicious 
 methods of cultivation, or when in chemical analysis it 
 is extracted, the soils become light-colored. 
 
 The red color of soils is imparted by ferric oxide ; the 
 yellow, by smaller amounts of the same material. A 
 greenish tinge is supposed to be due to the presence 
 of ferrous compounds, such soils being so close in tex- 
 ture as to prevent the oxidizing action of the air. Color 
 
PHYSICAL PROPERTIES OF SOILS 5 1 
 
 may serve, to a slight extent, as an index of fertility. 
 Black and yellow soils are, as a rule, the most produc- 
 tive, although occasionally black soils are unproductive 
 because of the presence of acid compounds injurious to 
 vegetation. The main reason why black soils are so 
 generally fertile is because they contain a high per cent 
 of humus and nitrogen. 
 
 49. Odor and Taste of Soils. — Soils containing liberal 
 amounts of organic matter have characteristic odors due 
 to the presence of aromatic bodies produced by the 
 decomposition of organic matter. In cultivated soils 
 these have a neutral reaction. The amount of aromatic 
 compounds in soils is very small. Poorly drained peaty 
 soils give off volatile acid compounds when dried. 
 
 The taste of soils varies with the chemical composi- 
 tion. Peaty soils usually have a slightly sour taste, due 
 to the presence of organic acids. Alkaline, soils have 
 variable tastes according to the prevailing alkaline com- 
 pound. The taste of a soil frequently reveals a fault, 
 as acidity or alkalinity. 
 
 50. Power of Soils to absorb Gases. — All soils pos- 
 sess, to a variable extent, the power of absorbing gases. 
 When decomposing animal or vegetable matter is mixed 
 with soil, the gaseous products given off are absorbed. 
 Absorption is the result of both chemical and physical 
 action. The chemical changes which occur, as the fixa- 
 tion of ammonia, are considered in the chapter on fixa- 
 
52 SOILS AND FERTILIZERS 
 
 tion. The organic matter of the soil is the principal 
 agent in the physical absorption of gases ; peat has the 
 power of absorbing large amounts. This action is sim- 
 ilar to that of a charcoal filter in removing noxious 
 gases from water, 
 
 51. Relation of Soils to Electricity. — There is always 
 a certain amount of electricity in both the soil' and the 
 air. The part which it takes in plant growth is not 
 well understood. The action of a strong current upon 
 the soil undoubtedly results in a change in chemical 
 composition, but in order to change the composition of 
 the soil so as to render the unavailable plant food 
 available, a current destructive to vegetation would be 
 required. When plants are subjected to too strong a 
 current of electricity, they wilt and have all of the after- 
 effects of frost. A feeble current has either an indif- 
 ferent or a slightly beneficial effect upon crop growth, 
 but not sufficient to warrant its use in general crop 
 production on account of cost, and it is undoubtedly 
 physiological rather than chemical in its action unless 
 it be in the favorable influence exerted upon nitrifica- 
 tion. The electrical conductivity of soils has been taken 
 by Whitney as the basis for the determination of mois- 
 ture.^^ It is, however, dependent largely upon the nature 
 and amount of dissolved salts. 
 
 52. Importance of the Physical Study of Soils. — A 
 
 study of the physical properties of soils gives much val- 
 
PHYSICAL PROPERTIES OF SOILS 53 
 
 liable information regarding their probable agricultural 
 value ; but while the physical properties should always 
 be taken into consideration, they should not form the 
 sole basis for judging the character of a soil, because 
 two soils from the same locality frequently have the 
 same general physical composition, although entirely 
 different crop-producing power, due to differences in 
 chemical composition and amounts of available plant 
 food. It is not possible from a physical analysis alone 
 to determine the agricultural value of a soil. 
 
 Attempts have been made to overestimate the value 
 of the physical properties of soils and to explain nearly 
 all soil phenomena on the basis of soil physics, but 
 important as are the physical properties, it cannot be 
 said they are of more importance than the chemical or 
 bacteriological. In fact, the four sciences, chemistry, 
 physics, geology, and bacteriology, are all closely con- 
 nected and each contributes its part to our knowledge 
 of soils. 
 
CHAPTER II 
 
 GEOLOGICAL FORMATION AND CLASSIFICATION OF 
 SOILS 
 
 53. Agricultural Geology. — The geological study of 
 a soil concerns itself with the past history of that soil, 
 the materials out of which it has been produced, together 
 with the agencies which have taken part in its forma- 
 tion and distribution. Geologically, soils are classified 
 according to the period in the earth's history when 
 formed, and also according to the agencies which have 
 distributed them. The principles of soil formation and 
 distribution should be understood, because of their im- 
 portant bearing upon fertility. Agricultural geology 
 forms a separate branch of agricultural science ; in this 
 work only a few topics especially relating to soils are 
 treated. 
 
 54. Formation of Soils. — Geologists state that the 
 surface of the earth was at one time soUd rock. It is 
 held that soils have been formed from- rock by the 
 joint action of the various agents : (i) heat and cold, 
 (2) water, (3) gases, (4) micro-organisms and other forms 
 of vegetable and animal life, and (5) wind. One of the 
 best evidences that soil is derived from rock is that there 
 
 54 
 
GEOLOGICAL STUDY OF SOILS 55 
 
 are frequently found pieces which are rotten, and, when 
 crushed, closely resemble the prevailing soil of the 
 field. This is particularly true of clay soils where there 
 are fragments of disintegrated feldspar that when 
 crumbled are similar to the soil in which the feldspar 
 was embedded. The process of soil formation is ex- 
 tremely slow and the various agents have been at work 
 for an almost unlimited period. 
 
 Weathering is the joint action upon rocks of the vari- 
 ous atmospheric agencies. Some rocks are more sus- 
 ceptible to it than others, and in different localities even 
 the same kind of rock may vary in the rapidity with 
 which it responds to weathering. 
 
 55. Action of Heat and Cold. — The cooling of the 
 earth's surface, followed by a contraction in volume, 
 resulted in the formation of fissures which exposed a 
 larger area to the action of other agencies. The un- 
 equal cooling of the rocks caused a partial separation 
 of the different minerals of which the rocks were com- 
 posed, resulting in the formation of smaller rock parti- 
 cles from the larger rock masses. This is well illustrated 
 by the familiar splitting and crumbling of stones when 
 heated. Shaler estimates that a variation of 150° F. 
 will make a difference of i inch in the length of a 
 granite ledge 100 feet long. As a result of changes in 
 temperature there is a lessening in cohesion of the rock 
 particles. The action of frost also is favorable to soil 
 formation. The freezing of water in rock crevices 
 
56 
 
 SOILS AND FERTILIZERS 
 
 results in breaking up the rock masses, forming smaller 
 bodies. The force exerted by water when it freezes is 
 sufficient to rend large rocks. 
 
 56. Physical Action of Water. — Water acts upon soils 
 both chemically and physically. It is the most impor- 
 
 
 9H 
 
 
 
 r "■" ^^ 
 
 
 
 
 ' ' ^ 
 
 ^ 
 
 
 %t 
 
 
 
 ^^H 
 
 f^ 
 
 
 
 L. 
 
 '\ 
 
 M->^. 
 
 
 
 .^ ,.„>''■. 
 
 ■ - 
 
 
 
 V, 1^ 
 
 *jSjfi 
 
 ■ 
 
 
 
 ^Mk 
 
 A 
 
 ■Mi 
 
 
 m 
 
 'flj 
 
 
 PHgpS:^^^ 
 
 ^'-.^ ^9m 
 
 Fig. 19. Boulder split by Frost. 
 (Minnesota Geological and Natural History Survey.) 
 
 tant agent that takes a part in soil formation. The sur- 
 face of rocks has been worn away by moving water and 
 in many cases deep ravines and canons have been 
 formed. This is called erosion. The pulverized rock, 
 being carried along by the water and deposited under 
 favorable conditions, forms alluvial soil. This physical 
 
GEOLOGICAL STUDY OF SOILS 
 
 57 
 
 action of water is illustrated in the workings of large 
 rivers where the pulverized rock particles are deposited 
 along the river and at its mouth. Large areas of the 
 soil in valleys and river bottoms have been formed in 
 
 Fig. 20. Granite Bluff shattered by Frost. 
 (Minnesota Geological and Natural History Survey.) 
 
 this way, and in most cases these soils are of high fertil- 
 ity. The action of water is not alone confined to form- 
 ing soils along water courses, but is equally prominent 
 in the formation of soils remote from streams or lakes, 
 as in the case of soils deposited by glaciers. 
 
 57. Glacial Action. — At one time in the earth's history, 
 the ice fields of polar regions covered much larger areas 
 
58 SOILS AND FERTILIZERS 
 
 than at present-^*^ Changes of climate caused a recession 
 of these, and resulted in the movement of large bodies 
 of ice, carrying along rocks and frozen soil. The move- 
 ment and pressure of the ice pulverized the rock and 
 produced soil. This action is well illustrated at the 
 present time where mountains rise above the snow line, 
 and the ice and snow melting at the base are replaced by- 
 ice and snow from farther up, moving down the side of 
 the mountain and carrying along crushed stones and 
 soil. King estimates that an ice sheet lo feet in depth 
 exerts a pressure of 570 pounds to the square foot. The 
 frozen mass contains boulders, gravel, and sand which 
 act as a grinding plate upon the rocky surfaces with 
 which it comes in contact.^^ The rubbing of these two 
 surfaces against each other under pressure for cen- 
 turies has resulted in the production of vast areas of 
 drift soil. 
 
 When the glacier receded, stranded ice masses were 
 distributed over the land. These melted slowly and by 
 their grinding action hollowed out places some of which 
 finally became lakes. The numerous lakes at the source 
 of the Mississippi River are supposed to have been 
 formed by glacial action. The terminal of a glacier is 
 called a moraine and is covered with large boulders 
 which have not been disintegrated. The course of a 
 glacier is frequently traced by the markings or scratches 
 of the mass on rock ledges. In glacial soils, the rocks 
 are never angular, but are smooth because of the grind- 
 
GEOLOGICAL STUDY OF SOILS 59 
 
 ing action during transportation. The area of glacial 
 soils in the northern portion of the United States is 
 quite large. These soils are, as a rule, fertile because of 
 the pulverization and mixing of a great variety of rock. 
 
 58. Chemical Action of Water. — The chemical action 
 of water is an important factor in soil formation. While 
 nearly all rocks are practically insoluble in water there 
 is always some material dissolved, evidenced by the fact 
 that all spring water contains dissolved mineral matter. 
 When charged with carbon dioxide and other gases, 
 water acts as a solvent upon rocks ; it converts many 
 oxides, as ferrous oxide, into hydroxides, and produces 
 new compounds more soluble or readily disintegrated, 
 as deposit^ of clay, which have been formed from feld- 
 spar rock by the chemical and physical action of water. 
 Rock decay is often dependent upon chemical change ; 
 the addition of water, or hydration of the molecule, par- 
 ticularly of the silicates, is one of the most important 
 chemical changes. When rocks, as feldspar, disinte- 
 grate, there is an addition of 12 to 14 per cent of water 
 of hydration to the disintegrated products. This chem- 
 ical union of water with the rock materials entirely 
 changes their properties and often prepares the way 
 for other chemical changes. Water takes as prominent 
 a part in the decay of rocks as in the decay of vegeta- 
 ble matter. Dissolved minerals produce many chemical 
 changes in both rocks and soils. The chemical action 
 of fertilizers, known as fixation, can take place only 
 
60 SOILS AND FERTILIZERS 
 
 when the substances are in sokition. In fact, water is 
 necessary for nearly all the chemical reactions in the 
 soil which result in rendering plant food available. 
 
 59. Joint Action of Air and Gases. — In the disintegra- 
 tion of materials to form soil, air takes a prominent 
 part. By the aid of oxygen, carbon dioxide, and other 
 gases and vapors in the air, rock disintegration is has- 
 tened. The action of oxygen changes the lower oxides 
 to higher forms. All rock contains more or less oxygen 
 in chemical combination. The carbon dioxide of the air 
 under some conditions favors the formation of carbon- 
 ates. The disintegrating action of air, moisture, and 
 frost is illustrated in the case of building stones which 
 in time crumble and form a powder. Many of the 
 benefits of cultivation are due to aeration of the soil, as 
 air promotes chemical changes of mineral substances 
 and prepares the way for life processes in the soil. 
 
 60. Action of Micro-organisms. — Micro-organisms, 
 found on the surface and in the crevices of rocks, are 
 active agents in bringing about rock decay, deriving all 
 of their energy from the chemical changes which they 
 induce between minerals, and obtaining their carbon 
 from the air. Such organisms incorporate organic 
 matter with the rock residues.^^ Certain nitrifying 
 organisms can obtain their nitrogen also from the air, 
 and it is believed that they have largely prepared the 
 way for the production of agricultural plants, by incor- 
 
GEOLOGICAL STUDY OF SOILS 6l 
 
 porating the initial stores of carbon and nitrogen of the 
 air with the disintegrated rock materials. 
 
 61. Action of Vegetation. — Some of the lower forms 
 of plants, as lichens, do not require soil for growth, but 
 are capable of living on the bare surface of rocks, 
 obtaining food from the air, and leaving a certain 
 amount of vegetable matter which undergoes decay and 
 is incorporated with the rock particles, preparing the 
 way for higher orders of plants which take their food 
 from the soil. When this vegetable matter decays, it 
 enters into chemical combination with the pulverized 
 rock, forming humates.^^ The disintegrating action of 
 plant roots and vegetable matter upon rocks has been 
 an important factor in soil formation. The action of 
 vegetable remains in soil production is discussed in 
 Chapter III. 
 
 62. Earthworms. — Many soils have been greatly 
 modified by the action of earthworms. The soil in 
 passing through their digestive tract is ground into finer 
 particles and is intimately mixed with the indigestible 
 matter excreted by the worms. In the case of rich loam 
 soils it is estimated that all of the particles have at 
 some time passed through the digestive tract of earth- 
 worms. Where they have been active, air and water 
 are admitted into the soil more readily. The action of 
 earthworms in soils has been extensively studied by 
 Darwin. 
 
62 SOILS AND FERTILIZERS 
 
 63. Wind. — Wind also has been an important factor 
 in the production and modification of soils. The denud- 
 ing effects of heavy wind storms are well known. 
 Large areas of- wind-formed soils are found in some 
 countries. Sand dunes are transported by winds, and 
 often their subjugation by soil-binding plants is neces- 
 sary in order to prevent encroachment upon valuable 
 farm lands and inundation of villages. Soils formed by 
 the action of winds are called aeolian soils. 
 
 64. Combined Action of the Various Agents. — In the 
 decay of rocks the various agents named ^ — water act- 
 ing mechanically and chemically, heat and cold, air, 
 micro-organisms, vegetation, earthworms, and wind — 
 have acted jointly, and have produced more rapid disin- 
 tegration than if each agent had acted separately. 
 
 DISTRIBUTION OF SOILS 
 
 65. Sedentary and Transported Soils. — The place 
 which a soil occupies is not necessarily where it was 
 formed ; that is, a soil may be produced in one locality 
 and transported to another. Soils are either sedentary 
 or transported. Sedentary soils are those which occupy 
 the original position where they were formed. They 
 usually have but little depth before rock surface is 
 reached. The stones in such soils, except where modi- 
 fied by weathering, have sharp angles because they 
 have not been ground by transportation. In the south- 
 
GEOLOGICAL STUDY OF SOILS 
 
 63 
 
 ern part of the United States, east of the Mississippi 
 River, there are large areas of sedentary soils as fer- 
 rogenous clays in an advanced state of decay. 
 
 Transported soils are those which have been formed 
 
 Fig. 22. A Boulder-filled Channel. 
 (Minnesota Geological and Natural History Survey.) 
 
 in one locality and carried by various agents as gla- 
 ciers, rivers, or winds to other localities, the angles of 
 the stones in these soils having been ground off during 
 transportation. Transported soils are divided into 
 classes according to the ways in which they have been 
 formed ; as drift soils produced by glaciers, alluvial soils 
 by rivers and lakes, aeolian soils by winds, and colluvial 
 soils formed of rocks and debris from mountain sides. 
 
64 SOILS AND FERTILIZERS 
 
 In some localities volcanic soils are found. They are 
 extremely varied in texture and composition; some are 
 very fertile and contain liberal amounts of alkaline salts 
 and phosphates, while others contain so little plant food 
 that they are sterile. 
 
 ROCKS AND MINERALS FROM WHICH SOILS ARE 
 FORMED 
 
 66. Composition of Rocks. — Rocks are composed of 
 either a single mineral or of a combination of minerals. 
 Most of the common minerals are definite chemical 
 compounds and have a varied range in composition, 
 due to the fact that one element or compound may be 
 partially or entirely replaced by another. Most rocks 
 from which soils have been derived contain minerals, as 
 feldspar, mica, hornblende, and quartz. 
 
 67. Quartz. ^ — -Quartz is the principal constituent of 
 many rock formations. Pure quartz is silicic anhydride, 
 SiOa, and a soil formed from pure quartz alone would 
 be sterile. White sand is nearly pure quartz or silica. 
 Silica enters into combination with many elements, 
 forming a large number of minerals. Particles of quartz 
 when cemented with iron compounds form sandstone 
 rock. Sand is derived mainly from the decay of rocks 
 containing quartz. 
 
 68. Feldspar is composed of silica, alumina, and 
 potash or soda. Lime may also be present, and replace 
 
GEOLOGICAL STUDY OF SOILS 6$ 
 
 a part or nearly all of the soda. If the mineral contains 
 soda as the alkaline constituent, it is known as albite, 
 or if mainly potash, it is called potash feldspar or 
 orthoclase. 
 
 The members of the feldspar group are insoluble in 
 acids, and before disintegration takes place are not 
 capable of supplying plant food. Potash feldspar con- 
 tains from 12 to 15 per cent of potash, none of which is 
 of value as plant food until disintegrated. When feld- 
 spar undergoes disintegration, it produces kaolin or clay. 
 A soil formed from feldspar is usually well stocked with 
 potash. Feldspar containing lime readily yields to the 
 solvent action of water in which there is carbon dioxide. 
 
 Orthoclase, AlKSigOg Potash feldspar 
 
 Albite, AlNaSisOg Sodium feldspar 
 
 69. Hornblende. — The hornblende and augite groups 
 are formed by the union of magnesium, calcium, iron, 
 and manganese, with silica. As a rule none of the 
 members of the alkali family are present in hornblende. 
 The augites are double silicates of iron, manganese, cal- 
 cium, and magnesium. Quite frequently, phosphoric 
 acid is in chemical combination with the iron. The 
 members of this group are readily distinguished by 
 their color, which is black, brown, or brownish green. 
 The hornblendes which contain lime are quite readily 
 decomposed when subjected to weathering and the 
 action of water charged with carbon dioxide. They are 
 
66 SOILS AND FERTILIZERS 
 
 mainly insoluble in acids, and do not as a rule form 
 very fertile soils. 
 
 70. Mica. — Mica is quite complex in composition, 
 is an abundant mineral, and is composed of silica, iron, 
 alumina, manganese, calcium, magnesium, and potas- 
 sium. Mica is a polysilicate. The color may be white, 
 brown, black, or bluish green, owing either to the ab- 
 sence of iron, or to its presence in various amounts. 
 The chief physical characteristic of the members of this 
 group is the ease with which they are split into thin 
 layers. It is to be observed that the mica group con- 
 tains all the elements of both feldspar and hornblende. 
 Mica is quite resistant to chemical change. 
 
 Soils formed from thoroughly disintegrated mica are 
 usually fertile, owing to the variety of essential elements 
 present. 
 
 71. Granite is composed of quartz, feldspar, and 
 mica. It is a very hard rock and slow to disintegrate. 
 The different shades of granite depend upon the pro- 
 portion in which the various minerals are present. 
 Inasmuch as it contains so many minerals, it usually 
 follows that granite soil is fertile ; although when not com- 
 pletely disintegrated or when disintegrated and leached, 
 it is unproductive. Pure powdered granite before un- 
 dergoing disintegration furnishes but little plant food. 
 After weathering, the plant food gradually becomes 
 available. Granite varies in both physical and chemi- 
 
GEOLOGICAL STUDY OF SOILS 6/ 
 
 cal composition, and some disintegrates more readily 
 than others. Gneiss belongs to the granite series, but 
 differs from true granite in containing a large amount 
 of mica. Mica schist contains a larger amount of mica 
 than gneiss, 
 
 72. Zeolites. — The zeolites are a large group of sec- 
 ondary or derivative minerals formed from disintegrated 
 rock. They are polysilicates containing alumina and 
 members of the alkali and lime families, and all contain 
 water held in chemical combination. They are partially 
 soluble in dilute hydrochloric acid and belong to that class 
 of compounds which are capable, to a certain extent, of 
 becoming available as plant food. In color, they are white, 
 gray, or red. Zeolites are quite abundant in clay and are 
 an important factor in soil fertility. It is this group of 
 hydrated silicates which takes such an important part in 
 the process of fixation. The zeolites, when disintegrated, 
 particularly by glacial action, form very fertile soils. 
 
 73. Apatite or Phosphate Rock. — Apatite is com- 
 posed mainly of phosphate of lime, Ca3(P04)2, together 
 with small amounts of other compounds, as fluorides 
 and chlorides. It is generally of a green or yellow 
 color and is present in many soils, but is of little value 
 as plant food unless associated with organic matter and 
 soluble alkaline salts. 
 
 74. Kaolin is chemically pure clay and is formed by 
 the disintegration of feldspar. When feldspar is de- 
 
68 SOILS AND FERTILIZERS 
 
 composed and acted upon by water, the potash is re- 
 moved and water of hydration is taken up, forming the 
 product kaolin, which is hydrated silicate of alumina, 
 Al4(Si04)3 . HgO. Impure varieties of clay are colored 
 red and yellow owing to the presence of iron and 
 other impurities. Pure kaolin is white, is insoluble in 
 acids, and is incapable of supplying any nourishment to 
 plants. Clay soils are fertile on account of the other 
 minerals and organic matter mixed with the clay and are 
 usually well stocked with potash because of its incom- 
 plete removal from the disintegrated feldspar. It is to 
 be observed that the term ' clay ' used chemically means 
 aluminum silicate, while physically it is any substance 
 the particles of which are less than 0.005 i^^i- i^^ diameter. 
 
 75. Limestone. — Limestone is present in many sec- 
 ondary rocks. It is composed of calcium carbonate and 
 is slowly soluble in water containing carbon dioxide. 
 Extensive deposits of calcium carbonate, as limestone, 
 marble, and chalk, occur in nature. It is widely dif- 
 fused in soils, and is a constituent that imparts fertiUty. 
 Many soils contain appreciable amounts of disintegrated 
 limestone. 
 
 76, Disintegration of Rocks and Minerals. — In ad- 
 dition to the rocks and minerals which have been 
 mentioned, there are many others that contribute to soil 
 formation, as glauconite, a hydrated siHcate of iron ; 
 alumina and potash ; limonite, a hydrated oxide of 
 
GEOLOGICAL STUDY OF SOILS 
 
 69 
 
 iron ; dolomite, a double carbonate of calcium and mag- 
 nesium; serpentine, a silicate of magnesium; and gypsum 
 calcium sulphate. All rocks and minerals are subject to 
 disintegration and change in chemical composition and 
 physical properties. The process of soil formation has 
 resulted in numerous chemical and physical changes. 
 These changes are still taking place, and as a result 
 plant food is constantly being made available. 
 
 Chemical Composition of Rocks" 
 
 
 < 
 
 < 
 z 
 
 
 29. 
 
 ^9 
 
 < 
 
 go 
 
 < Ml 
 
 a 
 a 
 
 
 u 
 
 go 
 
 u v 
 
 a 
 
 <9. 
 
 Quartz . . . 
 Feldspar . . 
 
 95-100 
 
 55-67 
 46 
 
 40-45 
 40-55 
 60-80 
 
 20-29 
 39 
 
 12-37 
 
 0-15 
 
 10-15 
 
 
 
 
 
 
 
 0-12 
 
 I-IO 
 
 I-II 
 
 
 
 
 CS') 
 
 14 
 
 Apatite . . 
 Mica 
 
 
 53 
 
 
 5-12 
 
 4-5 
 
 
 1-5 
 
 
 
 
 
 
 
 
 2-3 
 
 
 
 
 
 
 77. Value of Geological Study of Soils. — Agricul- 
 tural geology is a valuable aid in studying soil prob- 
 lems, but like other sciences it is incapable alone of 
 solving all the problems of soil fertility. Means have 
 not yet been devised for accurately determining the 
 extent of rock disintegration and the rapidity with 
 which it has taken place or the degree to which dis- 
 
70 SOILS AND FERTILIZERS 
 
 integrated minerals have been removed from rocks by 
 leaching and other agencies. It js known that the 
 rate of weathering of soils is influenced by various fac- 
 tors, as origin, texture, composition, humidity and other 
 climatic conditions, presence of decaying organic matter, 
 micro-organisms, mechanical treatment and manipula- 
 tion of the soil, fertilizers, sunlight and vegetation. 
 Some of these agencies for promoting soil disintegra- 
 tion are under the control of the farmer and are utilized 
 by him in rendering plant food available. A knowledge 
 of the origin of soils, of the minerals of which they are 
 composed, and of the ways in which they have been 
 distributed is of much assistance in determining their 
 agricultural value. 
 
CHAPTER III 
 
 THE CHEMICAL COMPOSITION OF SOILS 
 
 78. Elements Present in Soils. — Physically consid- 
 ered, a soil is composed of disintegrated rock mixed 
 with animal and vegetable matter; chemically con- 
 sidered, the rock particles consist of a large number of 
 simple and complex compounds, each compound being 
 composed of elements chemically united. Elements 
 unite to form compounds, compounds to form minerals, 
 minerals to form rocks, and disintegrated rock forms 
 soil. When rocks decompose, the disintegration, except 
 in a few cases, is never carried to the extent of liberating 
 the elements, but the process ceases when the minerals 
 have been broken up into compounds. While there are 
 present in the crust of the earth between 6$ and 70 
 elements, only about 1 5 are found in animal and plant 
 bodies, and of these but 12 are known to be absolutely 
 essential. Only four of the elements which are of most 
 importance are at all liable to be deficient in soils. 
 These four elements are : nitrogen, phosphorus, potas- 
 sium, and calcium. 
 
 79. Classification of the Elements. — The elements 
 found most abundantly in soils are divided into two 
 classes : 
 
 71 
 
72 SOILS AND FERTILIZERS 
 
 Acid-forming Elements Base-forming Elements 
 
 Oxygen O Aluminum Al 
 
 Silicon Si Potassium K 
 
 Phosphorus P Sodium Na 
 
 Sulphur S Calcium Ca 
 
 Chlorine CI Magnesium Mg 
 
 Nitrogen N Iron Fe 
 
 Hydrogen H 
 
 Carbon C 
 
 Boron, fluorine, manganese, and barium are usually 
 present in small amounts, besides others which may be 
 found in traces, as the rare elements lithium and 
 titanium. 
 
 For crop purposes the elements of the soil may be 
 divided into three classes : 
 
 1. Essential elements most liable to be deficient; 
 nitrogen, potassium, phosphorus, and calcium. 
 
 2. Essential elements usually abundant ; iron, mag- 
 nesium, and sulphur. 
 
 3. Unnecessary and accidental elements, usually 
 abundant; as chlorine, silicon, aluminum, and man- 
 ganese. 
 
 80. Combination of Elements. — In dealing with the 
 composition of soils, the percentage amounts of the 
 individual elements are not given, except m the case of 
 nitrogen, but instead, the amounts of the correspond- 
 ing oxides. The elements do not exist in a free state 
 in soils, but are combined with oxygen and other 
 elements to form compounds. When considered as 
 
THE CHEMICAL COMPOSITION OF SOILS 
 
 73 
 
 oxides, the acid and basic constituents may form various 
 compounds as : 
 
 Calcium 
 
 Potassium 
 Sodium . 
 Magnesium 
 Iron . . 
 
 Silicate 
 
 Phosphate 
 
 Chloride 
 
 Sulphate 
 
 Carbonate 
 
 The following reactions will explain some of the more 
 elementary combinations : 
 
 CaO + SiOa = CaSiOg 
 3CaO + P2O5 = CagCPO^)^ 
 CaO + SOg =CaS04 
 CaO + CO2 = CaCOg 
 
 CaO + N2O5 = Ca(N0g)2 
 
 K2O + SOg 
 
 Na20 + SOg 
 
 MgO + SOg = MgSO^ 
 
 K2SO, 
 Na2S04 
 
 It is often difficult to determine with accuracy the 
 exact form or combination in which an element is 
 present in the soil. When reported as the oxide, bases 
 may be considered as combined with any of the ox- 
 ides of the acid-forming elements, as indicated by 
 the reactions, to form salts. Each compound of 
 an element may have a different value as plant food, 
 hence it is important to determine as far as possible 
 the form or solubility of the various elements of plant 
 food. 
 
74 SOILS AND FERTILIZERS 
 
 ACID-FORMING ELEMEJ!TTS 
 
 81. Silicon. — The element silicon makes up from 
 a quarter to a third of the solid crust of the earth and 
 next to oxygen is the most abundant element found in 
 soils. Silicon never occurs in the soil in the free state. 
 It either combines with oxygen to form silica (SiOg), or 
 with oxygen and some base-forming element or elements 
 to form silicates. Silica and the various silicates are 
 by far the most abundant compounds present in the 
 soil. Silicon is not one of the elements absolutely 
 necessary for plant growth, and even if it were, all soils 
 are so abundantly supplied that it would not be necessary 
 to use it in fertilizers. 
 
 When two or more base-forming elements are united 
 with the siUcate radical, a double silicate results. The 
 double silicates are the most common compounds 
 present in soils. There are also a number of forms of 
 silicic acid which greatly increase the number of sili- 
 cates, and a study of the composition of soils is largely 
 a study of these various silicates. 
 
 82. Carbon is an acid-forming element and belongs to 
 the same family as silicon. It is found in the soil as 
 one of the main constituents of the volatile or organic 
 compounds, and also unites with oxygen and the base- 
 forming elements, producing carbonates, as calcium 
 carbonate or limestone. The carbon of the soil takes 
 no direct part in forming the carbon compounds of 
 
THE CHEMICAL COMPOSITION OF SOILS 75 
 
 plants. It is not necessary to apply carbon fertilizers 
 to produce the carbon compounds of plants, because 
 the carbon dioxide of the air is the source for crop 
 production. It is estimated that there are 30 tons 
 of carbon dioxide in the air over every acre of the 
 earth's surface.^ The carbon in the soil is an indirect 
 element of fertility, because it is usually combined with 
 other elements, as nitrogen and phosphorus, which are 
 absolutely necessary for crop growth. 
 
 83. Sulphur occurs in all soils mainly in the form of 
 sulphates, as calcium sulphate, magnesium sulphate, 
 and sodium sulphate. It is an essential element of 
 plant food. There is generally less than o.io per cent 
 of sulphuric anhydride in ordinary soils, but the amount 
 required by crops is small and there is usually an 
 abundance. 
 
 84. Chlorine is found in all soils, generally in com- 
 bination with sodium, as sodium chloride. It may be 
 in combination with other bases. Soils which contain 
 more than 0.2 per cent are, as a rule, sterile. Chlorine 
 is present in the soil in soluble forms. It occurs in all 
 plants but is not absolutely necessary for plant growth. 
 Its use in fertilizers is unnecessary, although chlorine 
 with sodium, as common salt, is sometimes used as an 
 indirect fertilizer. 
 
 85. Phosphorus, one of the essential elements for 
 plant growth, is combined with both the volatile and 
 
^6 SOILS AND FERTILIZERS 
 
 non-volatile elements of the soil. Plants cannot make 
 use of it in other forms than the phosphates. Phos- 
 phorus is usually present in the soil as calcium phos- 
 phate, magnesium phosphate, or aluminum phosphate, 
 and may also be combined with the humus, forming 
 humic phosphates. The form of the phosphates, as 
 available or unavailable, is an important factor in soil 
 fertility. Soils are quite liable to be deficient in phos- 
 phates, inasmuch as they are so largely drawn upon 
 by many cro-ps, particularly grain crops, where the 
 phosphates accumulate in the seed, and are sold from 
 the farm. The phosphorus content of soils is usually 
 reported as phosphorus pentoxide (P2O5), anhydrous 
 phosphoric acid, commonly called phosphoric acid. 
 
 86. Nitrogen. — This element is present in soils in 
 various forms. As a mineral constituent it is combined 
 with oxygen and the base-forming elements as potas- 
 sium, sodium, and calcium, forming nitrates and nitrites, 
 which, on account of their solubility, are never found 
 in average soils in large amounts. Nitrogen is mainly 
 in organic combination, being associated with carbon, 
 hydrogen, and oxygen as one of the elements form- 
 ing the organic matter of soils. Nitrogen may also 
 be present in small amounts in the form of ammonia, or 
 of ammonium salts, derived from rain water and from 
 the decay of vegetable and animal matter. While free 
 nitrogen is in the air in large amounts, it can be ap- 
 propriated as food in this form by only a limited num- 
 
THE CHEMICAL COMPOSITION OF SOILS "JJ 
 
 ber of plants and by them indirectly. For ordinary 
 agricultural crops, particularly the cereals, nitrogen 
 must be present in the soil as combined nitrogen. This 
 is the most expensive of any of the elements of plant 
 food, and is liable to be deficient. No other element 
 takes such an important part in agriculture or in life 
 processes as does nitrogen. 
 
 87. Oxygen. — Oxygen is combined with both the 
 acid- and base-forming elements and is found in nearly 
 all of the compounds of the soil. It has been estimated 
 that about one half of the crust of the earth is com- 
 posed of oxygen, which in large amounts is combined 
 with silicon, forming silica. That which is held in 
 chemical combination in the soil takes no part in the 
 formation of plant tissue. In addition to being present 
 in the soil, oxygen constitutes eight ninths of the weight 
 of water and about one fifth of the weight of air. It 
 also forms about 50 per cent of the compounds found 
 in plants and animals. Oxygen in the interstices of the 
 soil is an active agent in bringing about many chemical 
 changes, as oxidation of the organic matter, and disin- 
 tegration of the soil particles. 
 
 88. Hydrogen. — This element is never found in a 
 free state in the soil, but is combined with carbon and 
 oxygen in animal and vegetable matter, with oxygen to 
 form water, and in a few cases with some of the base 
 elements to form hydroxides. It is not in the soil in 
 
y2> SOILS AND FERTILIZERS 
 
 large amounts, and that which forms a part of the 
 tissues of plants and animals comes from the hydrogen 
 in water. Hydrogen in the organic matter of soils takes 
 no part directly in producing the hydrogen compounds 
 of plants. On account of its lightness, hydrogen never 
 makes up a very large proportion, by weight, of the 
 composition of bodies. 
 
 BASE-FORMING ELEMENTS 
 
 89. Aluminum is present in the soil in the largest 
 amount of any of the base elements. It forms probably 
 from 6 to lo per cent of the solid crust of the earth. 
 As previously stated aluminum is one of the constituents 
 of clay, and is not necessary for plant growth. Physi- 
 cally, however, the aluminum compounds take an im- 
 portant part in soil fertility. Aluminum is usually in 
 combination with silica or with silica and some base- 
 forming element, as iron, potassium, or sodium. The 
 various forms of aluminum silicate are the most numer- 
 ous compounds found in soils. Alumina is the oxide of 
 aluminum, AlgOg, and is the usual form in which this 
 element is reported in soil and rock analyses. 
 
 90. Potassium is in the soil mainly in the form of 
 silicates, and is one of the elements absolutely necessary 
 for plant growth. The term 'potash' (potassium oxide, 
 K2O) is usually employed when reference is made to 
 the potassium compounds. The amount and form of 
 
THE CHEMICAL COMPOSITION OF SOILS 79 
 
 the soil potash have an important bearing upon fertihty. 
 Potassium is one of the three elements of plant food 
 usually supplied in fertilizers. The form in which it is 
 in the soil and its economic supply as plant food are 
 important factors in crop production. The amount of 
 potash in soils ranges from 0.02 to 0.8 per cent. In a 
 fertile soil it rarely falls below 0.2 per cent. 
 
 91. Calcium is in the soil in a variety of forms, as 
 calcium carbonate, calcium silicate, calcium sulphate, 
 and calcium phosphate. The calcium oxide, CaO, of 
 the soil is generally spoken of as the lime content. 
 Calcium carbonate and sulphate are important factors 
 in imparting fertility. A subsoil with a good supply of 
 lime will stand heavy cropping and remain in excellent 
 chemical and physical condition for crop growth. In a 
 good soil there is usually 0.2 per cent or more of lime, 
 mainly as calcium carbonate. 
 
 92. Magnesium is found in all soils and is usually 
 associated with calcium, forming the mineral dolomite, 
 which is a double carbonate of calcium and magnesium. 
 Magnesium may also be present in the soil in the form 
 of magnesium sulphate or magnesium chloride. All 
 crops require a certain amount of magnesia in some 
 form, in order to reach maturity and produce fertile 
 seeds. There is generally in all soils an amount suffi- 
 cient for crop purposes, hence it is not necessary to 
 consider this element in connection with fertilizers. 
 
80 SOILS AND FERTILIZERS 
 
 The term 'magnesia' (magnesium oxide, MgO) is used 
 when reference is made to the magnesium compounds 
 of the soil. 
 
 93. Sodium is in the soil mainly as sodium silicate, 
 and to about the same extent as potassium, which it 
 resembles chemically in many ways. It cannot, how- 
 ever, replace potassium in plant growth. Inasmuch as 
 sodium takes an indifferent part in plant nutrition, it 
 is never used as a fertilizer except in an indirect way. 
 
 94. Iron is an element necessary for plant food and is 
 found in all soils to the extent of from i to 4 per cent. 
 Crops require only a small amount of iron, hence there 
 is always sufficient for crop purposes. Iron in soils is 
 in the form of oxides, hydroxides, and silicates. 
 
 FORMS OF PLANT FOOD 
 
 95. Three Classes of Compounds. — For agricultural 
 purposes, the compounds present in soils may be divided 
 into three classes :^ ( i ) Compounds soluble in water and 
 dilute organic and mineral acids ; (2) compounds soluble 
 in more concentrated acids ; (3) insoluble compounds 
 decomposed by strong acids and fluxes. 
 
 96. Water- and Dilute Acid-soluble Matter of Soils. — 
 
 This class includes silicates and other compounds of 
 potash, soda, lime, magnesia, phosphorus, etc., which are 
 
THE CHEMICAL COMPOSITION OF SOILS 
 
 soluble in the soil water and in very dilute organic and 
 mineral acids, and represents the most soluble and the 
 
 most active and valuable 
 forms of plant food. There 
 is only a very small amount 
 in these forms. In loo 
 pounds of arable soil, rarely 
 more than 0.005 pound of 
 any one of the important 
 elements is soluble in the 
 soil water or more than 0.05 
 pound in dilute organic acids. 
 
 97. Acid-soluble Matter of 
 Soils. — The plant food of 
 the second class is in a some- 
 what more insoluble form, 
 and consists of compounds, 
 principally the zeolites, sol- 
 uble in hydrochloric acid of 
 23 per cent strength, sp. gr. 
 I. II 5. This represents the 
 limit of the solvent action 
 of the roots of plants.^ In 
 this class are included also 
 all the mineral elements 
 combined with the humus and soluble in dilute alkalies. 
 As a rule, not over 10 to 20 per cent of the total soil is 
 soluble in hydrochloric acid ; and the more important 
 
 Fig. 23. Oat Plant grown in soil 
 extracted with hydrochloric acid. 
 
82 SOILS AND FERTILIZERS 
 
 elements make up only a small part of this amount. In 
 200 samples of soil, the potash, nitrogen, lime, magnesia, 
 and phosphoric and sulphuric anhydrides amounted to 
 3.5 per cent ; in many fertile soils the sum of these is less 
 than 1.50 per cent. This means that in every 100 pounds 
 of soil there are only from 1.5 to 3.5 pounds which can 
 take any active part in the support of a crop, while 96 to 
 98.5 pounds are present simply as so much inert material, 
 and valuable only from a physical point of view. Not 
 all of the potash, for example, soluble in hydrochloric 
 acid is equally valuable. In fact, the acid represents 
 more than the Hmit of the crop's feeding power, when 
 there is not enough of more soluble forms to aid in the 
 first stages of growth. 
 
 98. Acid-insoluble Matter of Soils. — This class in- 
 cludes all of those compounds of the soil which require 
 the joint action of the highest heat and the strongest 
 chemicals in order to decompose them. The insoluble 
 residue obtained after digesting a soil with strong hydro- 
 chloric acid contains potash, soda, and limited amounts 
 of magnesia and phosphoric acid, with other elements 
 which are of no immediate value as plant food. When 
 seed was planted in soil extracted with strong hydro- 
 chloric acid, it made no growth after the reserve food in 
 the seed had been exhausted. A plant grown in such 
 a soil is shown in the illustration.^* (Fig- 23.) 
 
 The acid-insoluble matter of soils is capable of under- 
 going disintegration and in time may be changed to the 
 
THE CHEMICAL COMPOSITION OF SOILS 
 
 83 
 
 second or zeolitic class of silicates. This process, how- 
 ever, is too slow to be relied upon as an immediate 
 source of plant food. 
 
 In the following table are given the percentage 
 amounts of compounds soluble and insoluble in hydro- 
 chloric acid for a few typical soils :^ 
 
 Insoluble matter 
 Potash 
 Soda . 
 Lime . 
 Magnesia 
 Iron 
 
 Alumina 
 Phosphoric acid 
 Sulphuric acid 
 
 Wheat 
 Soil 
 
 Soluble 
 in HCl 
 
 63.07 
 0.54 
 0.45 
 2.44 
 1.85 
 4.18 
 7.89 
 0.38 
 O.I I 
 
 Insol- 
 uble 
 residue 
 
 2.18 
 
 3-55 
 0.36 
 0.25 
 0.78 
 5-54 
 
 0.24 
 
 Heavy Clay 
 Soil 
 
 Soluble 
 inHCl 
 
 8477 
 0.21 
 0.22 
 0.48 
 0.34 
 376 
 6.26 
 0.12 
 0.09 
 
 Insol- 
 uble 
 residue 
 
 346 
 2.95 
 0.16 
 0.47 
 0.72 
 
 S-44 
 0.08 
 0.25 
 
 Grass and 
 Grain Soil 
 
 Soluble 
 inHCl 
 
 84.08 
 0.30 
 0.25 
 0.51 
 0.26 
 2.56 
 2.99 
 0.23 
 0.08 
 
 Insol- 
 uble 
 residue 
 
 1.45 
 0.25 
 
 0-35 
 0.46 
 1.07 
 9.72 
 0.05 
 0.02 
 
 The insoluble matter, after digestion with hydro- 
 chloric acid, was submitted to fusion analysis, and the 
 figures given under insoluble residue represent the 
 amounts of potash, soda, etc., insoluble in the acid. In 
 the clay soil, 94 per cent of the total potash was in 
 forms insoluble in hydrochloric acid. 
 
 99. Soluble and Insoluble Potash and Phosphoric Acid. 
 
 — From the preceding table it is to be observed that 
 
84 SOILS AND FERTILIZERS 
 
 the larger portion of the potash in the soil is insoluble 
 in hydrochloric acid. A soil may contain from 2 to 3 
 per cent of total potash, and 90 per cent or more may be 
 in such firm chemical combination with aluminum, sili- 
 con, and other elements, as to resist the solvent action 
 of plant roots. The larger portion of the phosphoric 
 acid of the soil is soluble in hydrochloric acid. In some 
 soils, however, from 20 to 40 per cent is present as the 
 third class of compounds. When a soil is digested with 
 hydrochloric acid, the insoluble residue is usually a fine 
 gray powder. Some clay soils retain their red color 
 even after treatment with acids, showing that the iron 
 is in part in chemical combination with the more com- 
 plex silicates. 
 
 In order to decompose the insoluble residue obtained 
 from the treatment with hydrochloric acid, fluxes, as 
 sodium carbonate and calcium carbonate, are employed 
 which, at a high temperature, act upon the complex sili- 
 cates and produce silicates soluble in acids. Plants, 
 however, are unable to obtain food in such complex 
 forms of chemical combination. 
 
 100. Action of Organic and Dilute Mineral Acids upon 
 Soils. — Dilute organic acids, as a i per cent solution 
 of citric acid, have been proposed as solvents for the 
 determination of easily available plant food. It has 
 been shown in the case of the Rothamsted soils which 
 have produced 50 crops of grain without manure, and 
 which are markedly deficient in available phosphoric 
 
THE CHEMICAL COMPOSITION OF SOILS 85 
 
 acid, that a i per cent solution of citric acid dissolved 
 only 0.003 per cent of phosphoric acid while the soil 
 contained a total of 0.12 per cent. In the case of an 
 adjoining plot which had received phosphate manures 
 until the soil contained a sufficient amount of available 
 phosphoric acid to produce good crops, there was pres- 
 ent 0.03 per cent of phosphoric acid soluble in a i per 
 cent citric acid solution. ^^ 
 
 Dilute organic acids are, to a certain extent, capable 
 of showing deficiency of plant food. A soil which 
 has 0.03 per cent of potash or phosphoric acid sol- 
 uble in I per cent citric acid is, as a rule, well stocked 
 with these elements in available forms. Prairie soils 
 of high fertility yield from 0.03 to 0.05 per cent of 
 both potash and phosphoric acid soluble in dilute or- 
 ganic acids ; soils which are deficient in these elements 
 usually contain less than 0.0 1 per cent. 
 
 The action of a single organic acid of specific 
 strength cannot be taken as the measure of fertility 
 for all soils and crops alike, because different plants 
 do not have the same amount or kind of organic acid 
 in the sap. Of the various organic acids, citric pos- 
 sesses the greatest solvent action upon lime, magnesia, 
 and phosphoric acid, while oxalic has the strongest 
 solvent action upon the silicates. Tartaric acid ap- 
 pears to be less active as a solvent than either citric 
 or oxalic acid. The combined use of dilute organic 
 acids, as citric with hydrochloric (sp. gr. 1.115), will 
 generally give an accurate idea of the character of a 
 
86 SOILS AND FERTILIZERS 
 
 soil. A fifth-normal solution of hydrochloric, or of 
 nitric acid, has also been proposed ^ for determining 
 the available plant food of soils ; a soil that yields 
 less than 25 parts of phosphoric acid per million of 
 soil, as soluble in fifth-normal nitric acid, is deficient in 
 available phosphates. 
 
 The use of dilute organic acids renders it possible 
 to detect small amounts of readily soluble phosphoric 
 acid and potash. It has been stated that when a soil 
 has been manured a few years with a phosphate fer- 
 tilizer and brought into good condition as to available 
 phosphoric acid, a chemical analysis will fail to detect 
 any difference in the soil before and after the treat- 
 ment with fertilizer. In the case of hydrochloric acid 
 as a solvent, this is true, as an acre of soil to the depth 
 of one foot weighs about 3,500,000 pounds and 500 
 pounds of a phosphate fertilizer would increase the 
 total amount of phosphoric acid about 0.0002 per cent, 
 which is less than can be accurately determined by 
 analysis. When, however, a dilute organic acid is used, 
 only the more easily soluble phosphoric acid is dissolved, 
 and this readily allows fertilized and unfertilized soils to 
 be distinguished. By the use of dilute organic and min- 
 eral acids decided differences have been shown between 
 fertilized and unfertilized soils. 
 
 101. Sampling Soils. — A composite sample of the 
 soil of a field is obtained by taking several small samples 
 to a depth of 6 to 12 inches, from different places, and 
 
THE CHEMICAL COMPOSITION OF SOILS 
 
 87 
 
 uniting them to form one sample. Samples of subsoil 
 also are taken from the same places. There is usually 
 a sharp line of demarca- 
 tion between the surface 
 soil and subsoil. It is the 
 aim to secure in each case 
 as representative a sample 
 as possible. All coarse 
 stones and roots are re- 
 moved and a record is made 
 of the amount of these. 
 The soil is air-dried, the 
 hard lumps are crushed, 
 and the material mixed and 
 passed through a sieve with 
 holes 0,5 mm. in diameter. 
 Only the fine earth is used 
 for the chemical analysis. 
 
 102. Analysis of Acid- 
 soluble Extract of Soils. — 
 Ten grams of soil are 
 weighed into a soil diges- 
 tion flask, and 10 cc. hydro- 
 chloric acid (sp. gr. I. II 5) 
 are added for every gram of soil used. The soil digestion 
 flask is then placed in a hot-water bath and the digestion 
 carried on for twelve to thirty-six hours at the temperature 
 of boiling water.^^ After digestion is completed the 
 
 Fig. 25. 
 
 Soil Flask and 
 tion of Soils. 
 
S8 SOILS AND FERTILIZERS 
 
 contents of the flask are transferred to a filter and sepa- 
 rated into the insohible part, and the acid solution which 
 contains the soluble compounds of the various elements. 
 The table on page 89 gives a general idea of the 
 process of soil analysis. One half of the acid solution 
 is used for obtaining the metals as noted on page 89. 
 The second half is divided into two portions, — the 
 first portion to be used for the determination of phos- 
 phoric acid, which is precipitated with ammonium 
 molybdate, and the second portion to be used for the 
 determination of sulphuric acid, which is precipitated 
 as barium sulphate. The carbon dioxide is determined 
 in a fresh portion of the original soil, the acid being 
 liberated with hydrochloric acid and the carbon dioxide 
 retained by absorbents and weighed. The nitrogen 
 and humus are determined in separate portions of the 
 original soil. The analysis of soils involves the use of 
 accurate and well-known methods of analytical chem- 
 istry, a discussion of which would not be germane to 
 this work. 
 
 103. Value of Soil Analysis. — Opinions differ as to 
 the value of soil analysis. It is claimed by some that 
 a chemical analysis of a soil is of no practical value 
 because it fails to give the amount of available plant 
 food. A soil may have, for example, 0.4 per cent of 
 potash soluble in hydrochloric acid and still not con- 
 tain sufficient available potash to produce a good crop, 
 while another soil may contain 0.2 per cent of potash 
 
THE CHEMICAL COMPOSITION OF SOILS 
 
 89 
 
 ^ ^ 
 
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 C- en 
 
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 =" O rt « 
 
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 c^ .^ 
 
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 X 
 
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 v; o3 rt 03 .S T! CXd 
 
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 '■§ a § "So 
 
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 ^ -k^ OJ 
 
 o ° o 2 s 
 
 o c/2 cxc: 03 
 
 1 d 1^ <u ^ 
 
 •- " OJ 03 =2 
 
 'm -a ^ 3 13 a, 
 Pi 
 
90 SOILS AND FERTILIZERS 
 
 soluble in hydrochloric acid and produce good crops. 
 While these conditions are frequently observed, it does 
 not necessarily follow that the chemical analysis of a 
 soil is of no value, as often the results are not correctly 
 interpreted. Then, too, other solvents than hydro- 
 chloric acid are used for determining the more active 
 forms of plant food. Hydrochloric acid is generally 
 used because it represents the limit of the solvent power 
 of plants.^ The figures obtained by the hydrochloric 
 acid solvent are valuable, as they indicate whenever an 
 element is present in amounts too limited for crop pro- 
 duction. Suppose a soil contain 0.02 per cent of acid- 
 soluble potash ; this would be too small an amount to 
 produce good crops. On the other hand, the soil might 
 contain 0.5 per cent and yet not have sufficient avail- 
 able potash for crop growth. Hence it is that in 
 interpreting results, the hydrochloric acid solvent may 
 show when a soil is wholly [deficient in any one ele- 
 ment, as sometimes occurs, but it does not necessarily 
 show a deficiency in the case of a soil rich in acid- 
 soluble potash ; this can, however, be approximately 
 indicated, by the use of other solvents, as explained 
 in previous sections. Hydrochloric acid is mainly val- 
 uable in determining the general character of the soil, 
 rather than its amount of available plant food. 
 
 104. Interpretation of Soil Analysis. — In the analysis 
 of soils their reaction as acid, alkaline, or neutral, should 
 be determined, because plant food exists in a different 
 
THE CHEMICAL COMPOSITION OF SOILS 9I 
 
 form in each class of soils. If a soil contain from 0.3 
 to 0.5 per cent or more of lime and from o.i to 0.4 per 
 cent of combined carbon dioxide, and is not strongly- 
 alkaline, there is a reasonable content of lime car- 
 bonate. If, however, the soil contain only a trace of 
 carbon dioxide, the lime is not present as carbonate, but 
 probably as a silicate, in which case the soil may be 
 deficient in active lime compounds. 
 
 In the case of phosphoric acid, a soil which gives an 
 alkaline or neutral reaction, contains 0.15 per cent of 
 phosphorus pentoxide and is well supplied with organic 
 matter and lime, is amply provided with phosphoric acid, 
 and under such conditions the use of phosphate ferti- 
 lizers is not required, except possibly for special crops. 
 Hilgard states that should the per cent of phosphoric 
 acid be as low as 0.05, there is, in all probability, a 
 deficiency of this element. It frequently happens that 
 in acid soils the phosphoric acid is unavailable until a 
 lime fertilizer is used to neutralize the acid. 
 
 Soils containing less than 0.07 per cent of total 
 nitrogen are usually deficient, and one containing as 
 high as 0.15 or 0.2 per cent may fail to respond to 
 crop production, but such a case is generally due to 
 some abnormal condition of the soil, as lack of alkahne 
 compounds which are necessary for nitrification. The 
 appearance of the crop is one of the best indications as 
 to deficiency of nitrogen. 
 
 A soil which contains less than o.io per cent of 
 potash soluble in hydrochloric acid is quite apt to be 
 
92 SOILS AND FERTILIZERS 
 
 deficient in this element. Soils which contain 0.5 per 
 cent or more of lime carbonate will produce good crops 
 on a smaller working supply of potash than soils which 
 are deficient in lime. As a rule the best agricultural 
 soils contain from 0.3 to 0.6 per cent of potash, Sandy- 
 soils of good depth may contain less plant food than the 
 figures given, and not be in need of fertilizers. 
 
 The best results are obtained from soil analysis when 
 an extended study is made of the soils of a locality. 
 Then a soil of that region which fails to produce good 
 crops can be compared with a productive soil of known 
 composition. An isolated soil analysis, like an isolated 
 analysis of well water, frequently fails in its object 
 because of a lack of proper normal standards for com- 
 parison. Where extended series of soil analyses have 
 been made, much valuable information has been obtained. 
 
 The term * volatile matter ' of a soil is sometimes incor- 
 rectly used for organic matter. The volatile matter in- 
 cludes the organic matter and also the water which is held 
 in chemical combination, as in the hydrated silicates. 
 A soil may have a high per cent of volatile matter and 
 contain very little organic matter. Indeed, all clays 
 contain from 5 to 9 per cent of water of hydration. 
 The per cent of humus, as will be explained in the next 
 chapter, does not represent all of the organic matter. 
 
 105. Total and Available Plant Food. — Suppose a 
 soil contain 0.40 per cent of acid-soluble potash and 
 field experiments indicate there is a deficiency of 
 
THE CHEMICAL COMPOSITION OF SOILS 93 
 
 available potash. This may be due to some abnormal 
 condition of the soil, as an insufficient amount of other 
 alkaline compounds, as calcium carbonate, to take the 
 place of the potash which has been withdrawn by the 
 crop, or lost by leaching, in which case the deficiency of 
 available potash can be remedied without purchasing 
 soluble potash fertilizer. Where a soil contains only 
 0.04 per cent of acid-soluble potash, the purchasing of 
 potash fertilizers is more necessary, but with 0.40 per 
 cent the way is open to render this available for crops. 
 The various ways of rendering acid-insoluble potash and 
 other compounds available for crop production, as by 
 rotation of crops, use of farm manures, use of lime and 
 green manures, or by different methods of cultivation 
 have not been sufficiently studied as yet to offer a solu- 
 tion to all of the problems of rendering inert plant food 
 available. 
 
 106. Distribution of Plant Food. — In studying the 
 chemical composition of a soil, the surface soil and sub- 
 soil both require consideration. It frequently happens 
 that these have entirely different chemical, as well as 
 physical, properties, and that a soil fault, as lack of 
 potash in the surface soil, is corrected by a high per 
 cent of that element in the subsoil. This is particularly 
 true of some of the prairie soils, where the surface soils 
 generally contain less potash and lime, but more nitrogen 
 and phosphoric acid, than the subsoils. When jointly 
 considered the surface and subsoil have a good supply 
 
94 SOILS AND FERTILIZERS 
 
 of available plant food, but if considered separately each 
 would have weak points. 
 
 Since plant food is obtained mainly from the silt and 
 clay, the amount present in these grades of particles 
 determines largely the reserve fertility of a soil. A 
 soil in which 70 per cent of the total potash is present 
 in the silt and clay is in better condition for crop pro- 
 duction than a similar soil with a like amount of potash 
 which is present mainly in the sand. Because a soil 
 has a given composition, it does not follow that all of 
 the different grades of particles have the same composi- 
 tion. In fact, the different grades of soil particles in 
 one soil may have as varied a composition as is met 
 with among different soils-^*^ 
 
 The figures under i in the table give the composition 
 of the particles, while under 2 are the results calculated 
 on the basis of the total amount of each element in the 
 soil. For example, the clay contains 1.47 per cent of 
 potash, while 50.8 per cent of the total potash of the 
 soil is in the clay particles. 
 
 A soil may contain a low per cent of an element, 
 mainly in the finer particles and evenly distributed so 
 the crop is better supplied with food than if more were 
 present in the larger particles, unevenly distributed. 
 The distribution of plant food in the soil has not been 
 so extensively studied as the question of total plant 
 food. The distribution of plant food in both surface 
 soil and subsoil, as well as in the various grades of 
 soil particles, is an important factor of fertility. 
 
THE CHEMICAL COMPOSITION OF SOILS 
 
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g6 SOILS AND FERTILIZERS 
 
 107. Composition of Typical Soils. — A few examples 
 are given, in tabular form, of the chemical composition 
 of soils from different regions in the United States, On 
 account of variations in the same locality, the figures 
 represent the composition of only limited soil areas. 
 There have been made in the United States a large 
 number of soil analyses which as yet have not been 
 compiled or studied in a systematic way. 
 
 108. Alkaline Soils. — When a soil contains enough 
 alkaline salts, as sodium sulphate, sodium or potassium 
 carbonate or chloride, to be destructive to vegetation, 
 it is called an 'alkali' soil. These soils are found in 
 semi-arid regions, and wherever conditions have been 
 such that the alkaline compounds have not been drained 
 from the soil. Occasionally calcium chloride is the 
 destructive material. Sodium sulphate is a milder form. 
 Alkaline carbonates are destructive to vegetation when 
 present to the extent of more than i part per looo parts 
 of soil. When evaporation takes place, the alkaline 
 compounds are deposited as a coating on the surface 
 of the soil. Of these sodium carbonate is one of the 
 most injurious; it exerts a solvent action upon the 
 humus, forming a black solution which evaporates and 
 leaves the so-called 'black alkali.' Many soils sup- 
 posed to be strongly alkaHne, because a white coating 
 is formed on the surface, simply contain so much lime 
 carbonate that a deposit is formed. Excellent soils have 
 been passed over as ' alkali ' soils when in reality they 
 are limestone soils. 
 
THE CHEMICAL COMPOSITION OF SOILS 
 
 97 
 
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98 
 
 SOILS AND FERTILIZERS 
 
 
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THE CHEMICAL COMPOSITION OF SOILS 99 
 
 109. Improving Alkali Soils.^^ — When a large tract of 
 alkali is to be brought under cultivation, the amount and 
 kind of prevailing alkaline compound should be deter- 
 mined by chemical analysis. It frequently happens that 
 improved drainage, coupled with a judicious irrigation 
 system, is all the treatment necessary. If the prevail- 
 ing alkali is sodium carbonate, a dressing of land plaster 
 may be appHed so as to change the alkali from sodium 
 carbonate to sodium sulphate, a less destructive form, 
 the reaction being 
 
 Na2C03 + CaS04 = CaCOg + NaaSO^. 
 
 Some shrubs, as greasewood, and weeds, as Russian 
 thistle, take from the soil large amounts of alkahne 
 matter, and it is sometimes advisable to remove a num- 
 ber of such crops so as to reduce the alkali. A shghtly 
 beneficial effect is occasionally noticed on small * alkali ' 
 spots where straw has been burned and the ashes used, 
 forming potassium silicate. As a rule, however, ashes 
 are more injurious than beneficial on an 'alkali' soil. 
 Irrigation and thorough drainage, if continued long 
 enough, will effect a permanent cure. Irrigation with- 
 out drainage causes a worse alkaline condition by bring- 
 ing to the surface subsoil alkali. All irrigated lands 
 should be provided with suitable drainage systems to 
 prevent accumulation of alkaline salts. The waters 
 from some streams and wells are unsuited for irrigation 
 because they contain too much alkaline matter. 
 
 Mildly alkaline soils will usually repay in crop pro- 
 
lOO SOILS AND FERTILIZERS 
 
 duction all the labor which is expended upon them, and 
 when brought under cultivation are frequently very 
 fertile. Some alkaline material in a soil is beneficial; 
 in fact, many soils would be more productive if they 
 contained a small amount. It is the excess of alkali 
 that is destructive to plant life. 
 
 When the places are small and located so they can 
 be underdrained at comparatively little expense, this 
 should be done, as it will prove the best and most per- 
 manent way of removing the alkali. Good surface 
 drainage should also be provided. Quite frequently a 
 quarter or more of the total alkali in the soil will, in a 
 dry time, be found near and on the surface. In such 
 cases, and if the spots are small, a large amount of the 
 alkali can be removed by scraping the surface and then 
 carting the scrapings away and dumping them where 
 they can do no damage. 
 
 When preparing a mildly alkaline spot for a crop, 
 deep plowing should be practiced, so as to open up 
 the soil and remove the excess of alkali from the sur- 
 face. Where manure, particularly horse manure, can be 
 obtained, these spots should be manured very heavily. 
 The horse manure, when it decomposes, furnishes acid 
 products, which combine with the alkaline salts. The 
 manure also prevents rapid surface evaporation. Oats 
 are about the safest grain crop to seed on an alkali spot 
 because the oat plant is capable of thriving in an alka- 
 line soil where many other grain crops fail. 
 
 Alkali soils are usually deficient in available nitro- 
 
THE CHEMICAL COMPOSITION OF SOILS Id 
 
 gen. The organism which carries on the work of 
 changing the humus nitrogen to available forms cannot 
 thrive in a strohg alkaline solution. In many of these 
 soils, as demonstrated in the laboratory, nitrification 
 cannot take place. After thorough drainage and prepa- 
 ration for a crop, a few loads of good soil from a fertile 
 field sprinkled on alkali spots will do much to encourage 
 nitrification, by introducing the nitrifying organisms. 
 
 For a more extended account of the cause of alkali 
 soils, and methods for improving them, the student is 
 referred to Hilgard's " Soils." 
 
 110. Acid Soils. — When a soil is deficient in active 
 alkali, and there is an excess of organic material, humic 
 acid is formed from the decay of the animal and vege- 
 table matter. Acid soils are readily detected by the 
 reaction which they give with sensitive litmus paper. 
 In making the test the moistened soil is pressed against 
 blue litmus paper, which changes to red in the presence 
 of free acids. Acid soils are made productive by using 
 lime and other alkaline material to neutralize the humic 
 acid before applying farm and other manures. Acid soils 
 are not suitable for the production of clover and legumes. 
 
 Experiments by Wheeler at the Rhode Island Ex- 
 periment Station indicate that there are large areas 
 of acid soils in the eastern states which are much 
 improved when treated with air-slaked lime.^^ There 
 is great difference in the power of plants to live in 
 acid soils. Some agricultural crops as legumes are par- 
 
I02 SOILS AND FERTILIZERS 
 
 ticularly sensitive, while many weeds have such strong 
 power of endurance that they thrive in the presence of 
 acids. Weeds frequently reflect the character of a soil 
 as to acidity, in the same way that an alkali soil is 
 indicated by the plants produced. The acid and alka- 
 line compounds of the soil greatly influence the bacterial 
 flora. In the presence of strong acids or alkalis, many 
 of the bacterial changes necessary for the elaboration of 
 plant food fail to take place. 
 
 THE ORGANIC COMPOUNDS OF SOILS 
 
 111. Sources of the Organic Compounds of Soils. — 
 The organic compounds of soils are composed of the 
 elements carbon, hydrogen, oxygen, and nitrogen. 
 When vegetable and animal material undergoes decay 
 in contact with the soil, compounds, as carbon dioxide, 
 water, ammonia,^^ organic acids, and various derivatives 
 are formed, while some of the organic acids unite with 
 the. minerals of the soil to form humates. Micro- 
 organisms take an important part in the decay of ani- 
 mal and vegetable matter and the production of organic 
 compounds. In some soils, the organic compounds of 
 plants, as cellulose, proteids, and carbohydrates, are 
 present, while in others they have undergone partial 
 oxidation. Some authorities claim that a portion of the 
 initial organic matter of soils is the result of the work- 
 ings of carbon assimilating micro-organisms. The main 
 source of the soil's organic compounds, however, is the 
 
THE CHEMICAL COMPOSITION OF SOILS IO3 
 
 accumulated animal and vegetable remains in various 
 stages of decay. The organic matter of soils is a 
 mechanical mixture of a large number of organic com- 
 pounds, many of which have not yet been studied. 
 
 112. Classification of the Organic Compounds. — Vari- 
 ous attempts have been made to classify the organic 
 compounds of the soil. An old classification by 
 Mulder ^^ was humic, ulmic, crenic, and approcrenic 
 acids. None of these contain more than 4 per cent 
 nitrogen, while organic matter with 8 to 10 per cent 
 and in some cases 18 per cent is quite frequently 
 met with ; hence this classification is incomplete as it 
 includes only a part of the organic compounds of the 
 soil. For practical purposes the organic compounds of 
 soils may be divided into three classes: (i) those of low 
 nitrogen content, i to 4 per cent of nitrogen ; (2) those 
 of medium nitrogen content, 5 to 10 per cent; and (3) 
 those of high nitrogen content, 11 to 20 per cent. 
 
 113. Humus. — The term ' humus ' is employed to 
 designate the most active of the organic compounds ; 
 it is the animal and vegetable matter of the soil in 
 intermediate forms of decomposition. From different 
 soils, it is extremely varied in composition ; in one soil 
 it may have been derived mainly from cellulose, while 
 in another from a mixture of cellulose, proteid bodies, 
 and other organic compounds. The term 'humus,' unless 
 quaHfied, is a very indefinite one. Humus is obtained 
 
I04 SOILS AND FERTILIZERS 
 
 by extracting the soil with a dilute alkali, as ammonium 
 hydroxide, after treating with a dilute acid to remove 
 the lime which renders the humus insoluble. 
 
 114. Humification and Humates. — When the animal 
 and vegetable matter incorporated with soils undergoes 
 decomposition, there is a union of some of the organic 
 compounds with the base-forming elements. The decay- 
 ing organic matter produces organic products of an acid 
 nature. The organic acids and the base-forming 
 products unite to form humates or organic salts, which 
 are neutral bodies. This process is humification.^^ 
 
 Humic acid + calcium carbonate = calcium humate + COg. 
 Humic acid + potassium chloride = potassium humate and solu- 
 ble chlorides. 
 
 That a union occurs between the organic matter and 
 the soil has been demonstrated by mixing with soils 
 known amounts of definite organic compounds and 
 various organic materials, as cow manure, green clover, 
 meat scraps, and sawdust, and allowing humification to 
 go on for a year or more. After humification had 
 taken place, the humus extracted from the soil con- 
 tained more potash and phosphoric acid, than were 
 present in the humus of the original soil and the humus- 
 forming material, showing a chemical change had taken 
 place between the organic matter and the soil. The 
 power of various organic substances to produce humates 
 is illustrated in the following table : ^^' ^^ 
 
THE CHEMICAL COMPOSITION OF SOILS 
 
 105 
 
 C01V mafui?-e Jnnnits : 
 
 In original manure and soil 
 
 In final humus product (after humifica- 
 tion) 
 
 Gain in humic forms 
 
 Green cloiier humus : 
 
 in original soil and clover ..... 
 
 In final humus product 
 
 Gain in humic forms 
 
 Afeal scrap humus : 
 
 In original meat scraps and soil . . 
 
 In final humus product 
 
 Gain .■ . . 
 
 Sawdust hu/iius : 
 
 In original sawdust and soil .... 
 
 In final humus product . . . . 
 Oat straw humus : 
 
 In original straw and soil 
 
 In final humus product 
 
 Wheat gliadiit humus : 
 
 In original gliadin and soil 
 
 In final humus product 
 
 Gain 
 
 Egg albjitnin humus : 
 
 In original albumin and soil .... 
 
 In final humus product 
 
 Gain 
 
 Humic Phos- 
 phoric Acid 
 
 Humic 
 Potash 
 
 Grams 
 
 Grams 
 
 1. 17 
 
 1.06 
 
 1.62 
 
 1.27 
 
 0.45 
 
 0.21 
 
 3.21 
 
 5.26 
 
 374 
 
 4-93 
 
 0-53 
 
 0-33 
 
 (Loss) 
 
 1.07 
 
 0.25 
 
 1. 18 
 
 0.36 
 
 O.II 
 
 O.II 
 
 0.85 
 
 0.67 
 
 0.78 
 
 0.70 
 
 1.02 
 
 2.42 
 
 1.03 
 
 2.41 
 
 1.055 
 
 0.19 
 
 1.220 
 
 0.24 
 
 0.165 
 
 0.05 
 
 I.OI 
 
 0.20 
 
 I. II 
 
 0.24 
 
 0.04 
 
io6 
 
 SOILS AND FERTILIZERS 
 
 115. Comparative Value and Composition of Humates. 
 — The humus produced from a nitrogenous material, 
 as meat scraps, is more valuable than from cellulose 
 bodies, as sawdust, because the former has greater 
 power of combining with the phosphoric acid and 
 potash of the soil. The non-nitrogenous compounds, 
 as cellulose, starch, and sugar, undergo fermentation but 
 seem to possess little, if any, power to form humates. 
 There is also a great difference in soils as to their 
 humus-producing power. Soils deficient in lime or al- 
 kaline compounds possess only a feeble power to pro- 
 duce humates. There is too a marked variation in 
 the composition of the humus from different kinds of 
 organic matter. Straw, sawdust, and sugar, materials 
 rich in cellulose and other carbohydrates, yield a humus 
 characteristically rich in carbon and poor in nitrogen. 
 Materials rich in nitrogen, like meat scraps, green clover, 
 and manure, produce a more valuable humus, rich in 
 nitrogen and possessing the power to combine with the 
 potash and phosphoric acid of the soil to form humates. 
 
 Composition of Humus produced by 
 
 
 Cow 
 
 manure 
 
 Green 
 
 clover 
 
 Meat 
 
 scraps 
 
 Wheat 
 flour 
 
 Oat 
 
 straw 
 
 Saw- 
 dust 
 
 Sugar 
 
 Carbon 
 Hydrogen 
 Nitrogen 
 Oxygen 
 
 41.95 
 6.26 
 6.16 
 
 45-63 
 
 54.22 
 
 3-40 
 8.24 
 
 34-14 
 
 48-77 
 
 4-30 
 
 10.96 
 
 35-97 
 
 51.02 
 3.82 
 5.02 
 
 40.14 
 
 54-3° 
 2.48 
 2.50 
 
 40.72 
 
 49.28 
 
 3-33 
 
 0.32 
 
 47-07 
 
 57-84 
 3-04 
 0.08 
 
 39-04 
 
 Total 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
THE CHEMICAL COMPOSITION OF SOILS 
 
 107 
 
 Carbon . 
 Hydrogen 
 Nitrogen 
 Oxygen . 
 
 Highest 
 
 57.84 
 
 6.26 
 
 10.96 
 
 47.07 
 
 Lowest 
 
 41.95 
 
 2.48 
 0.08 
 
 34-14 
 
 Difference 
 
 15.89 
 
 10.88 
 12.93 
 
 Variations in composition are noticeable. The hu- 
 mus produced from each material, as green clover, oat 
 straw, or sawdust, is different from that produced from 
 any other material. The humus from green clover is 
 very complex in nature. It contains both nitrogenous 
 and non-nitrogenous compounds, and each class has a 
 different action in humification processes; hence it fol- 
 lows that the green clover humus must be a complex 
 mixture of both nitrogenous and non-nitrogenous bodies. 
 
 The nature of the humus, whether nitrogenous or 
 non-nitrogenous, is important. Humus produced from 
 sawdust and humus from meat scraps may be taken as 
 types of non-nitrogenous and nitrogenous humus. 
 
 116. Value of Humates as Plant Food. — Various 
 opinions have been held regarding the actual value, as 
 plant food, of this product from partially decayed an- 
 imal and vegetable matter. Humus was formerly re- 
 garded as composed only of carbon, hydrogen, and 
 oxygen, and inasmuch as plants obtain these elements 
 from water and from the carbon dioxide of the air, no 
 value was assigned to it. Later investigators added 
 
io8 
 
 SOILS AND FERTILIZERS 
 
 volafilemamr 
 
 nitrogen to the list, but stated that the nitrogen, when 
 combined with the humus and before undergoing fer- 
 mentation, was of no value as plant food. 
 
 Recent investigations have proved that the mineral 
 elements combined with the organic matter of soils are 
 of value as plant food,^ and that crops grown on the 
 
 black soils of Russia 
 obtain a large part of 
 their mineral food 
 from organic combi- 
 nations.^'* Culture ex- 
 periments show that 
 plants like oats and 
 rye may obtain their 
 mineral food entirely 
 from humate sources. 
 Seeds when planted 
 in a mixture of pure 
 sand and neutral 
 humates from fertile 
 soils, produced per- 
 fect plants. In order 
 to secure normal con- 
 ditions, a little Hme 
 was added to prevent the formation of humic acid, and 
 the organisms found in fertile fields were introduced. 
 The following results are given of oats which were 
 grown when the only supply of mineral food was in 
 humate forms : 
 
 Ibtal /n30/ui?/e/iatfer 
 
 Fig. 26. Graphic Composition of 200 Soils, 
 showing the Proportional Amounts of the 
 Various Soil Constituents. 
 
 Nitrogen. 2. Potash. 3. Phosphoric 
 
 acid. 
 
THE CHEMICAL COMPOSITION OF SOILS 
 
 109 
 
 Nitrogen and Ash Elements^ 
 
 Nitrogen .... 
 
 Potash 
 
 Soda 
 
 Lime 
 
 Magnesia .... 
 Iron ..... 
 Phosphoric anhydride 
 Sulphuric anhydride 
 Silicon 
 
 In Six Oat 
 
 In Six Mature 
 
 Seeds 
 
 Plants 
 
 Gram 
 
 Gram 
 
 0.0040 
 
 0.0556 
 
 00013 
 
 0.0640 
 
 O.OOOI 
 
 0.0079 
 
 0.0002 
 
 0.0249 
 
 0.0005 
 
 o.oi 10 
 
 
 0.0064 
 
 0.0016 
 
 0.0960 
 
 O.OOOI 
 
 0.0090 
 
 0.0026 
 
 0.7300 
 
 The facts that plants feed on humate compounds, and 
 decaying animal and vegetable matter produce humates 
 from the inert potash and phosphoric acid of the soil, 
 have an important bearing upon crop production in 
 pointing out a way by which inert plant food may be con- 
 verted into more active and available forms. This 
 also explains that stable manure is valuable partly 
 because it makes the inert plant food of the soil more 
 available. 
 
 117. Mineral Matter combined with Humus. — When 
 the humus compounds are separated from a soil, they 
 contain appreciable amounts of phosphorus, potassium, 
 and compounds of other elements which are soluble in 
 the reagents used for obtaining the humus. If the 
 
no 
 
 SOILS AND FERTILIZERS 
 
 humus materials are precipitated and purified by wash- 
 ing, the impurities are largely removed and the mineral 
 elements which are chemically united with and form a 
 part of the humus can then be determined. Analyses 
 of eight samples of purified humus ash, from produc- 
 tive prairie soils, gave the following average : ^ 
 
 
 Per Cent 
 
 Ash (precipitated humus) 
 
 12.24 
 
 Composition of ash : 
 
 
 Silica 
 
 61.97 
 
 Potash, KoO . 
 
 
 
 
 
 
 
 7.20 
 
 Soda, NagO 
 
 
 
 
 
 
 
 8.13 
 
 Lime, CaO 
 
 
 
 
 
 
 
 0.09 
 
 Magnesia, MgO 
 
 
 
 
 
 
 
 0.36 
 
 Ferric oxide, Fe.^Oo . 
 
 
 
 
 
 
 
 3.12 
 
 Alumina, AUO^ 
 
 
 
 
 
 
 
 348 
 
 Phosphoric acid, PjO^ 
 
 
 
 
 
 
 
 12.37 
 
 Sulphuric acid, SO3 
 
 
 
 
 
 
 
 0.98 
 
 Carbonic acid, CO, 
 
 
 
 
 
 
 
 1.64 
 
 118. Amount of Plant Food in Humate Forms. — In a 
 
 prairie soil containing 3.5 per cent of humus there are 
 present 100,000 pounds of humus per acre. Combined 
 with this humus are from 500 to 1500 pounds each of 
 phosphoric acid and potash. Similar soils which have 
 been under long cultivation without the restoration of 
 any humus, contain from 300 to 500 pounds each of 
 humic potash and phosphoric acid.^ A decline in crop- 
 producing power has in many cases been brought 
 
THE CHEMICAL COMPOSITION OF SOILS I 1 1 
 
 about by the loss of the plant food combined with the 
 humus. 
 
 119. Loss of Humus. — Loss of humus from soils is 
 caused by oxidation and by fires. Any method of 
 cultivation which accelerates oxidation reduces the 
 humus content. In many of the western prairie soils 
 which have been under continuous grain cultivation 
 for thirty years or more, the amount of humus has been 
 reduced one half. Summer fallowing also causes a loss 
 of humus. When land is continually under the plow, 
 and no manures are used, the humus is rapidly oxidized, 
 and there is left in the soil only the organic matter that 
 is slow to decay. 
 
 Forest and prairie fires have been very destructive 
 to the organic compounds of the soil. A soil from 
 Hinckley, Minn., before the great forest fire of 1893, 
 showed 1.69 per cent humus and 0.12 per cent nitro- 
 gen. ^^ After the fire there were present 0.41 per cent 
 humus and 0.03 per cent nitrogen. The forest fire 
 caused a loss of 2500 pounds of nitrogen per acre. In 
 clearing new land, particularly forest land, there is 
 frequently an unnecessary destruction of humus mate- 
 rials. Instead of burning all of the vegetable matter, it 
 would be better economy to leave some in piles for 
 future use as manure. When all of the vegetable mat- 
 ter has been burned, two or three good crops are 
 obtained, but the permanent crop-producing power of 
 the land is reduced because of the loss of nitrogen and 
 
112 
 
 SOILS AND FERTILIZERS 
 
 humus. When the vegetable matter has been only 
 partially removed, the crops at first may be smaller, 
 but in a few years returns will be greater than if all 
 of the vegetable matter had been burned. 
 
 120. Physical Properties of Soils influenced by Humus. 
 
 — The physical properties of a soil may be entirely 
 changed by the addition or the loss of humus. The 
 influence of humus upon the weight, color, heat, and 
 water-retaining power of soils is discussed in the chap- 
 ter on the physical properties of soils. Soils reduced in 
 humus content have less power of storing up water and 
 resisting drought. This fact is illustrated in the follow- 
 ing table : ^^ 
 
 Per Cent Water 
 
 In Soil 
 
 After io Hours' 
 Exposure in 
 Tray, to Sun 
 
 Soil rich in humus (3.75 per cent) . . . 
 Adjoining soil poorer in humus (2.50 per cent) 
 
 16.48 
 12.14 
 
 6.12 
 3-94 
 
 121. Humic Acid. — In the absence of calcium car- 
 bonate or other alkaline material, the vegetable matter 
 of soils through processes of decay may form organic 
 acids destructive to the growth of some crops. The com- 
 position and physical properties of these organic acids 
 have never been determined, and the indefinite term 
 ' humic acid ' has been applied to them. Succinic acid 
 
THE CHEMICAL COMPOSITION OF SOILS 
 
 113 
 
 has been reported present in peaty soils. Acid soils 
 can be distinguished by their action upon blue litmus 
 paper, and the acidity can be readily corrected by the use 
 of lime or wood ashes. A soil may, however, give an 
 acid reaction and contain a fair amount of lime as a 
 silicate. Studies conducted by the Rhode Island Ex- 
 periment Station indicate that the areas of acid soils are 
 quite extensive. 
 
 Fig. 27. Humus from Old Soil. 
 
 122. Soils in Need of Humus. — Sandy and sandy 
 loam soils that have 
 been cultivated for a 
 number of years to 
 corn, potatoes, and 
 small grains without 
 rotation of crops or the 
 use of stable manures 
 are deficient in humus. Clay soils, as a rule, are not in 
 need of humus so much as loam and sandy soils. The 
 
 mechanical condition of 
 heavy clay is, however, im- 
 proved by the addition of 
 humus-forming material. 
 The addition of humus to 
 loam and sandy soils is 
 beneficial in preventing 
 drifting, because it binds together the soil particles. 
 There are but few arable soils, under ordinary cultiva- 
 tion, to which it is not safe to add humus-forming mate- 
 
 '==^-^^xy^e/7^^ 
 
 ' ■ .f'Cart'on- 
 
 jiL 
 
 
 Fig. 28. Humus from New Soil. 
 
114 
 
 SOILS AND FERTILIZERS 
 
 rials either alone or jointly with lime. Ordinary prairie 
 soils, for the first ten years after breaking, are usually 
 well supplied. Swampy, peaty, and muck soils contain 
 large amounts ; in fact, they are often overstocked and 
 are improved by reducing the humus content. 'Alkali' 
 soils are usually deficient in humus. 
 
 123. Active and Inactive Humus. — When soil has 
 been long under cultivation, and no manures have been 
 used, the nitrogen and mineral matters combined with 
 the humus are reduced. The humus from long-culti- 
 vated fields contains a higher per cent of carbon than 
 from well-manured or new land; it is also less active 
 because of the carbon which does not readily undergo 
 oxidation.^ 
 
 humos from 
 New Soil 
 
 Per cent 
 
 Humus from 
 Old Soil 
 
 Per cent 
 
 Carbon 
 
 Hydrogen 
 
 Oxygen 
 
 Nitrogen 
 
 Ash 
 
 Total humus material 
 
 44.12 
 6.00 
 
 35-16 
 8.12 
 6.60 
 
 5-3° 
 
 50.10 
 
 4.80 
 
 3370 
 6.50 
 4.90 
 
 3-38 
 
 124. Influence of Different Methods of Farming upon 
 Humus. — The system of farming has a direct effect 
 upon the humus content and the composition of the 
 
THE CHEMICAL COMPOSITION OF SOILS 
 
 115 
 
 soil. Where the crops are systematically rotated, live 
 stock is kept, and the manure judiciously used, the 
 crop-producing power of the land is not lowered, as in 
 the case of the one-crop system. The influence of dif- 
 ferent systems of farming upon the humus content and 
 other properties of the soil may be observed in the fol- 
 lowing table : ^^ 
 
 Character of Soil 
 
 3 
 
 
 u 
 0. 
 
 M c 
 
 
 
 Phosphoric acid 
 combined with 
 humus 
 Per cent 
 
 Ml 
 
 C 
 
 '•3 
 
 1. Cultivated thirty-five years; 
 
 rotation of crops and ma- 
 nure ; high state of pro- 
 ductiveness 
 
 2. Originally same as i ; con- 
 
 tinuous grain cropping for 
 thirty-five years ; low state 
 of productiveness . . . 
 
 3. Cultivated forty-two years ; 
 
 systematic rotation and 
 manure ; good state of pro- 
 ductiveness 
 
 4. Originally same as 3 ; culti- 
 
 vated thirty-five years ; no 
 systematic rotation or ma- 
 nure ; medium state of pro- 
 ductiveness 
 
 70 
 72 
 70 
 
 67 
 
 3-32 
 1.80 
 346 
 
 2.45 
 
 0.30 
 0.16 
 0.26 
 
 0.21 
 
 0.04 
 0.0 1 
 0.03 
 
 0.03 
 
 48 
 39 
 59 
 
 57 
 
CHAPTER IV 
 
 NITROGEN OF THE SOIL AND AIR, NITRIFICATION, 
 AND NITROGENOUS MANURES 
 
 125. Importance of Nitrogen as Plant Food. — The 
 illustration (Fig. 29) shows an oat plant which received 
 no nitrogen, while compounds containing potassium, 
 phosphorus, calcium, and other essential elements of 
 plant food were liberally supplied. Observe the pecul- 
 iar and restricted growth and the limited root develop- 
 ment. The leaves were yellowish, showing lack of 
 nitrogen for chlorophyll formation. 
 
 In the absence of nitrogen a plant makes no ap- 
 preciable growth. With only a limited supply, growth 
 is begun in a normal way ; but as soon as the available 
 nitrogen is used up, the lower and smaller leaves begin 
 gradually to die down from the tips, and all of the 
 plant's energy is centered in one or two leaves. In one 
 experiment when only a small amount of nitrogen was 
 supplied, the plant struggled along in this way for 
 about nine weeks, making a total growth of but six 
 and one half inches.^ Just at the critical point when 
 the plant was dying of nitrogen starvation, a few mil- 
 ligrams of calcium nitrate were given. In thirty-six 
 hours the plant showed signs of renewed life, the leaves 
 
 116 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES 11/ 
 
 assumed a deeper green, new growth was begun, and 
 finally four seeds were produced. 
 During the time of seed formation 
 more nitrogen was added, but with no 
 beneficial result. All of the essential 
 elements for plant growth were liber- 
 ally provided, except nitrogen, which 
 was very sparingly supplied, until near 
 the period of seed formation. 
 
 When plants have reached a certain 
 period in their development, and have 
 been starved for want of nitrogen, the 
 later application of this element does 
 not produce normal growth, as the en- 
 ergy of the plant appears to have been 
 used up in searching for food. Nitro- 
 gen, as well as potash, lime, and phos- 
 phoric acid, are all necessary while 
 plants are in the first stages of growth. 
 
 In the case of wheat, nitrogen is as- 
 similated more rapidly than are any 
 of the mineral elements. Before the 
 plant heads out, over 85 per cent of 
 the total nitrogen required has been 
 taken from thesoil.^*^ Corn also absorbs 
 all of its nitrogen from four to five 
 weeks before the crop matures. Flax 
 takes up 75 per cent during the first fifty days of 
 growth. ^^ 
 
 Fig. 29. Oat Plant 
 grown without Ni- 
 trogen. 
 
Il8 SOILS AND FERTILIZERS 
 
 Nitrogen is demanded by all crops ; it forms the chief 
 building material for the proteids of plants. In the ab- 
 sence of sufficient nitrogen, the rich green color is not 
 developed ; the foliage is of a yellowish tinge. Nitro- 
 gen is one of the constituents of chlorophyll, the green 
 coloring matter of plants ; hence when there is a lack of 
 nitrogen only a limited amount of chlorophyll can be 
 produced. Plants with large, well-developed leaves of 
 a rich green color are not suffering for this element. 
 Nitrogenous fertilizers have a tendency to produce a 
 luxurious growth of foliage, deep green in color. 
 
 ATMOSPHERIC NITROGEN AS A SOURCE OF PLANT 
 
 FOOD 
 
 126. Early Views. — In addition to carbon, hydrogen, 
 and oxygen, which form the organic compounds of 
 plants, it was known as early as the beginning of the 
 present century that plants also contain nitrogen. The 
 sources of carbon, hydrogen, and oxygen for crop pur- 
 poses were much easier to determine and understand 
 than the sources of nitrogen. Priestley, the discoverer 
 of oxygen, believed that the free nitrogen of the air 
 was a factor in supplying plant food. De Saussure ar- 
 rived at just the opposite conclusion. Neither of these 
 assumptions was convincing because methods of chem- 
 ical analysis had not yet been sufficiently perfected to 
 solve the question.^ 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES II 9 
 
 127. Boussingault's Experiments. — Boussingault was 
 the first to make a careful study of the subject. In a 
 prepared soil, free from nitrogen, and containing all of 
 the other elements necessary for plant growth,' he grew 
 clover, wheat, and peas, carefully determining the 
 nitrogen in the seed. The plants were allowed free 
 access to the air, being simply protected from dust, and 
 were watered with distilled water. But little growth 
 was made. At the end of two months the plants were 
 submitted to chemical analysis, and the amount of ni- 
 trogen present was determined. 
 
 The results are given in the following table :*^ 
 
 Nitrogen 
 
 Clover, 2 mos. 
 
 Clover, 3 mos. 
 
 Wheat, 2 mos. 
 
 Wheat, 3 mos. 
 
 Peas, 2 mos. 
 
 In Seed Sown 
 Gram 
 
 O.II 
 
 O.I 14 
 
 0.043 
 0.057 
 0.047 
 
 In Plant 
 Gram 
 
 0.12 
 
 0.156 
 
 0.04 
 
 0.06 
 
 O.IO 
 
 Gain 
 
 Gram 
 
 O.OI 
 0.042 
 -0.003 
 0.003 
 0.053 
 
 Boussingault concluded that when plants growing in 
 a sterile soil were exposed to the air, there was with 
 some a slight gain of nitrogen, but that the amount 
 gained from atmospheric sources was not sufficient to 
 feed the plant and allow it to reach full maturity. By 
 many these results were not accepted as conclusive. 
 
 Fifteen years later (1853) Boussingault repeated his 
 
I20 
 
 SOILS AND FERTILIZERS 
 
 experiments, but in a different way. The plants were 
 now grown in a large carboy with a limited volume of 
 air so as to cut off all sources of com- 
 bined nitrogen, as traces of ammonia, 
 nitrates, and nitrites. By means of 
 a second glass vessel {B, Fig. 30) the 
 carboy was kept liberally suppHed 
 with carbon dioxide, so that plant 
 growth would not be checked for 
 lack of this material. When experi- 
 ments were carried on in this way, 
 using a fertile soil, the plants reached 
 full maturity ; but when a soil free 
 Plants grown from nitrogcn was used, plant growth 
 was soon checked. A general sum- 
 mary of this work is given in the following table : ^^ 
 
 Fig. 30, 
 
 in Carboy 
 
 Nitrogen 
 
 
 In Seeds 
 Gram 
 
 In Plant 
 Gram 
 
 Loss 
 Gram 
 
 Dwarf beans .... 
 
 Oats 
 
 White lupines .... 
 Garden cress .... 
 
 O.IOOI 
 0.0109 
 0.2710 
 0.0013 
 
 0.0977 
 0.0097 
 0.2669 
 0.0013 
 
 — 0.0024 
 
 — 0.0012 
 
 — 0.0041 
 
 These experiments show that with a sterilized soil, 
 and all sources of combined atmospheric nitrogen cut 
 off, the free nitrogen of the air takes no part in the food 
 supply of the plant. . 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES 121 
 
 In 1854 Boussingault again repeated his experiments 
 on nitrogen assimilation. This time he grew the plants 
 in a glass case so constructed that there was free 
 circulation of air from which all combined nitrogen had 
 been removed. These experiments were similar to his 
 second series, except the plants were not grown in a 
 limited volume of air. The results obtained showed 
 that the free nitrogen of the air, under the conditions of 
 the experiment, took no part in the food supply of the 
 plants. If anything, there was less nitrogen recovered in 
 the dwarfed plants than there was in the seed sown. 
 
 128. Villa's Results. — About the same time Ville 
 carried on a series of experiments of like nature, but in 
 a different way, and arrived at just the opposite con- 
 clusion. His experiments indicated that plants are 
 capable of making liberal use of the free nitrogen of 
 the air for food purposes. The directly opposite con- 
 clusions of Boussingault and Ville led to a great deal of 
 controversy. The French Academy of Science took up 
 the question, and appointed a commission to review the 
 work of Ville. The commission consisted of six promi- 
 nent scientists. They reported that " M. Ville's con- 
 clusions are consistent with his labor and results."^^ 
 
 129. Work of Lawes and Gilbert. — A little later 
 Lawes and Gilbert carried on such extensive experi- 
 ments under a variety of conditions as to remove all 
 doubt regarding the plants' source of nitrogen. Plants 
 
122 SOILS AND FERTILIZERS 
 
 were grown in sterilized soils, in prepared pumice stone, 
 and in soils with a limited quantity of nitrogen beyond 
 that contained in the seed. Different kinds of plants 
 were experimented with. The work was carried on with 
 the utmost care and with apparatus so constructed as to 
 eliminate all disturbing factors. The results in the 
 aggregate clearly show that plants, when acting in a 
 sterile medium, are unable to make use of the free 
 nitrogen of the air for the production of organic 
 matter.^^ 
 
 130. Atwater's Experiments. — Atwater carried on 
 similar experiments in this country.*^ His results in- 
 dicate that when seeds germinate they lose a small part 
 of their nitrogen, and when legumes are grown in a 
 sterile soil, but are subsequently exposed to the air, a 
 fixation of nitrogen may occur. He ascribed this gain to 
 micro-organisms or other agencies. 
 
 131. Field and Laboratory Tests. — By a five years' 
 rotation of clover and other leguminous plants, Lawes 
 and Gilbert found a soil gained from 200 to 400 
 pounds of nitrogen per acre, in addition to that removed 
 in the crop, while land which produced wheat contin- 
 uously, gradually lost nitrogen. The amount in the 
 subsoil remained nearly the same. These facts plainly 
 indicated that crops like clover have the power of gain- 
 ing nitrogen from unknown sources. The results of 
 prominent German agriculturists led to the same con- 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES 1 23 
 
 elusion. It was known that wheat grown after clover 
 gave as good results as when nitrogenous manures were 
 used, but for many years this was unexplained. 
 
 Laboratory experiments with sterilized soils do not 
 represent the normal conditions of growing crops, where 
 all of the bacteriological agencies of the soil, the air, 
 and the plant are free to act. Experiments show that 
 these agencies have an important bearing upon plant 
 growth. 
 
 In the work of the different investigators prior to 
 1888, plants were grown mainly in sterilized soils, and 
 under such conditions they were unable to make use of 
 the free nitrogen of the air, except when the soils were 
 subsequently inoculated from the air. 
 
 132. Hellriegel's Experiments. — Hellriegel grew le- 
 guminous plants in nitrogen-free soils. One set of 
 plants was watered with distilled water, while another 
 had in addition small amounts of leachings from an old 
 loam field. The plants watered with distilled water 
 alone made but little growth, while those watered with 
 the loam leachings reached full maturity and contained 
 something like a hundred times more nitrogen than was 
 in the seed sown. The dark green color also was 
 developed, showing the presence of a normal amount of 
 chlorophyll. The roots of the plants had well-formed 
 swellings or nodules, while those that were watered with 
 distilled water alone had none. The loam leachings 
 contained only a trace of nitrogen.*^ 
 
124 
 
 SOILS AND FERTILIZERS 
 
 133. Experiments of Wilfarth. — Experiments by 
 Wilfarth give more exact data regarding the amount 
 of nitrogen taken from the air. Two plots of lupines 
 were grown ; one was watered with distilled water, while 
 the other received in addition a small amount of leach- 
 ings from an old lupine field. 
 
 Watered with Distilled Water 
 
 Watered with Distilled Water 
 AND Soil Leachings 
 
 Dry matter 
 Grams 
 
 Nitrogen 
 Grams 
 
 Dry matter 
 Grams 
 
 Nitrogen 
 Grams 
 
 0.919 
 0.800 
 0.921 
 1 .02 1 
 
 0.015 
 0.014 
 0.013 
 0.013 
 
 44-72 
 45.61 
 44.48 
 42-45 
 
 1.099 
 
 I-I53 
 1. 195 
 
 1-337 
 
 These experiments have been verified by many other 
 investigators until the fact has been estabHshed that 
 leguminous plants may, through the agency of micro- 
 organisms, make use of the free nitrogen of the air. 
 When legumes were grown in closed vessels and the air 
 was analyzed, it was found that there was a loss of 
 nitrogen from the air proportional to that gained by the 
 plants. 
 
 The work of Hellriegel was not accidental, but the 
 result of careful and systematic investigation. As early 
 as 1863 he observed that clover would develop along the 
 roadway in sand in which there was scarcely a trace of 
 combined nitrogen. 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES 1 25 
 
 134. Composition of Root Nodules. — The root nodules 
 referred to are particularly rich in nitrogen. In one 
 experiment, the light-colored and active ones contained 
 5.55 per cent, while those dark-colored and older con- 
 tained 3.21 per cent, and all the nodules of the root, 
 both active and inactive, contained 4.60 per cent nitro- 
 gen. The root itself contained 2.21 per cent.*^ 
 
 The root nodules also contain definite and character- 
 istic micro-organisms, and it was the spores of these or- 
 ganisms that were in the soil extract in both Hellriegel's 
 and Wilfarth's experiments. In the sterilized soils they 
 were not present. These organisms found in root nod- 
 ules are the essential agents which aid in the fixation of 
 the free nitrogen of the air, and in its ultimate use as 
 plant food. The nitrogen assimilated by the micro- 
 organisms in the nodules of the legumes is in part ap- 
 propriated by the crop, which unaided is incapable of 
 making use of the free nitrogen of the air. 
 
 135. Nitrogen in the Root Nodules returned to the 
 Soil. — Ward has shown that when clover roots decay, 
 the organisms and nitrogen present in the nodules are 
 distributed within the soil.^^ Hence, whenever a legu- 
 minous crop is raised, nitrogen is added to the soil 
 instead of being taken away, as in the case of a grain 
 crop. The amount of nitrogen returned to the soil by 
 a leguminous crop as clover varies with the growth 
 of the crop. In the roots of a clover crop a year old 
 there are from 20 to 30 pounds of nitrogen per acre. 
 
126 SOILS AND FERTILIZERS 
 
 while in the roots and cuhns of a dense clover sod, 
 two or three years old, there may be lOO pounds or 
 more of nitrogen, not including that which has been 
 added to the soil by the accumulative action of the crop. 
 Peas, beans, lucern, cow peas, and all legumes possess 
 the power of fixing the free nitrogen of the air by means 
 of micro-organisms. The micro-organisms associated with 
 one species, as clover, differ from those associated with 
 another, as lucern. The amount of nitrogen which the 
 various legumes return to the soil is variable. 
 
 Hellriegel's results are of the greatest importance to 
 agriculture, because they show how the free nitrogen of 
 the air can be utilized indirectly as food by crops unable 
 to appropriate it for themselves. 
 
 THE NITROGEN COMPOUNDS OF THE SOIL 
 
 136. Origin of the Soil Nitrogen. — The nitrogen of 
 the soil is derived chiefly from the accumulated remains 
 of animal and vegetable matter. The original source 
 of the soil nitrogen, that is, the nitrogen which furnished 
 food to support the vegetation from which our present 
 stock of soil nitrogen is obtained, was probably the free 
 nitrogen of the air. All of the ways in which the free 
 nitrogen of the air has been made available to plants of 
 higher orders which require combined nitrogen are not 
 known. It* is supposed, however, that this has been 
 brought about by the workings of lower forms of plant 
 life,and by micro-organisms. Whatever these agencies, 
 they do not appear to be active in a soil under high cul- 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES 12/ 
 
 tivation, because the tendency of ordinary cropping is to 
 reduce the supply of soil nitrogen. 
 
 137. Organic Nitrogen of the Soil. — In ordinary soils 
 the nitrogen is present mainly in organic forms com- 
 bined with the carbon, hydrogen, and oxygen as humus, 
 and to a less extent with the mineral elements, forming 
 nitrates and nitrites. The organic forms of nitrogen, 
 it is generally considered, are incapable of supplying 
 plants with nitrogen for food purposes until the process 
 known as nitrification has taken place. The nitrogenous 
 organic compounds in cultivated soils are derived mainly 
 from the undigested protein compounds of manure and 
 from the nitrogenous compounds in crop residues, and 
 are present mainly as insoluble proteids.^^ When de- 
 composition occurs, amides, organic salts, and other 
 allied bodies are without doubt produced as interme- 
 diate products before nitrification takes place. The or- 
 ganic nitrogen of the soil may be present in exceedingly 
 inert forms similar to that in leather, as in many peaty 
 soils where there are large amounts of inactive organic 
 compounds rich in nitrogen. In other soils the nitrogen 
 is less complex. The organic nitrogen of the soil may 
 vary in complexity from forms, like the nitrogen of urea, 
 which readily undergo nitrification, to forms like that in 
 peat, which nitrify with difficulty, 
 
 138. Amount of Nitrogen in Soils. — The fertility 
 of any soil is dependent, to a great extent, upon the 
 
128 SOILS AND FERTILIZERS 
 
 amount and form of its nitrogen. In soils of the 
 highest fertility there is usually present from 0.2 to 
 0.3 per cent of total nitrogen, equivalent to from 
 7000 to 10,000 pounds per acre to the depth of one 
 foot. Many soils of good crop-producing power contain 
 as low as 0.12 per cent. There is usually two or three 
 times more nitrogen in the surface soil than in the sub- 
 soil In sandy soils which have been allowed to decHne 
 in fertility, there may be less than 0.04 per cent. Of 
 the total nitrogen in soils there is rarely more than 2 
 per cent at any one time in forms available as plant 
 food.** A soil with 5000 pounds of total nitrogen per 
 acre may contain less than 100 pounds of available nitro- 
 gen soluble in the soil water, of which only a part is 
 assimilated by the roots of crops. Hence it is that a 
 soil may contain a large amount of total nitrogen, and 
 yet be deficient in available nitrogen. 
 
 139. Amount o4 Nitrogen removed in Crops. — The 
 amount of nitrogen removed in crops ranges from 25 to 
 100 pounds per acre, depending upon the nature of the 
 crop. It does not necessarily follow that the crop which 
 removes the largest amount of nitrogen leaves the land 
 in the most impoverished condition. Wheat and other 
 grains, while they do not remove so much in the crop, 
 leave the soil more exhausted than if other crops were 
 grown. This, as will be explained, is caused by the loss i 
 of nitrogen from the soil in other ways than through the 
 crop. 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES 129 
 
 Wheat, 20 bushels . 
 Straw, 2000 pounds 
 
 Total . 
 Barley, 40 bushels . 
 Straw, 3000 pounds 
 
 Total . 
 Oats, 50 bushels . . 
 Straw. 3000 pounds 
 
 Total . 
 Flax, 15 bushels . . 
 Straw, 1800 pounds . 
 
 Total . 
 Potatoes, 1 50 bushels 
 Corn, 65 bushels 
 Stalks, 3000 pounds 
 
 Total. 
 
 Pounds of 
 
 Nitrogen per 
 
 Acre removed 
 
 IN Crop^ 
 
 25 
 10 
 
 35 
 28 
 12 
 
 40 
 
 35 
 
 50 
 39 
 _^ 
 
 54 
 
 40 
 40 
 
 ii 
 
 75 
 
 140. Nitrates and Nitrites. — Nitrogen in the form of 
 nitrates and nitrites varies from mere traces to 150 
 pounds per acre. Soils with large amounts of nitroge- 
 nous humus and lime may contain for short periods as 
 high as 300 pounds of nitrates and 15 pounds of nitrites, 
 calculated as sodium salts. Some soils contain more 
 nitrates than are utilized by crops as food, and plants 
 may assimilate more than they can convert into protein, 
 
 K 
 
I30 SOILS AND FERTILIZERS 
 
 Wheat, corn, and other crops grown on rich soils may 
 contain both nitrates and nitrites as normal constituents. 
 King reports nitrates in the growing crop in much larger 
 amounts than in the soil water. As the crop matures 
 the nitrate content of the plant declines. Calcium ni- 
 trate is the usual form, especially in soils which are 
 sufficiently supplied with calcium carbonate to allow 
 nitrification to progress rapidly. Nitrates and nitrites 
 are the most valuable forms of nitrogen for plant food. 
 Both are produced from the organic nitrogen of the soil. 
 A nitrate is a compound composed of a base element as 
 sodium, potassium, or calcium, combined with nitrogen 
 and oxygen. A nitrite contains less oxygen than a nitrate. 
 Potassium nitrate, KNO3, sodium nitrate, NaNOg, 
 and calcium nitrate, Ca(N03)2 are the nitrates which 
 are of most importance in agriculture. The nitrites, as 
 potassium nitrite, KNOg, are present to a less extent 
 than the nitrates. Nitrates and nitrites are found in 
 surface well waters contaminated with animal and vege- 
 table matter. Many well waters possess some material 
 value as a fertilizer on account of the nitrates, nitrites, 
 and decaying animal and vegetable matters which they 
 contain. 
 
 141. Ammonium Compounds of the Soil. — The am- 
 monium compounds in a soil are usually less in amount j 
 than the nitrates and nitrites. The sources are rain 
 water and the organic matter of the soil. The am- 
 monium compounds are all soluble and readily undergo 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES I3I 
 
 fixation. See Chapter VI. They cannot accumulate 
 in arable soils, because of nitrification and fixation. 
 Usually they are to be found in surface well waters. 
 In the soil, the ammonium compounds are acted upon 
 by nitrifying organisms, and nitrites and nitrates are 
 formed. Such compounds as ammonium chloride or 
 ammonium carbonate, if present in a soil in excessive 
 amounts, will destroy vegetation in a way similar to 
 the alkaline compounds in alkaline soils, but in small 
 amounts they are beneficial. 
 
 142. Nitrogen in Rain Water and Snow. — Ordinarily 
 the nitrogen which is annually returned to the soil in 
 the form of ammonium compounds dissolved in rain 
 water and snow is equivalent to from 2 to 3 pounds 
 per acre. At the Rothamsted Experiment Station the 
 average amount for eight years was 3.37 pounds.** 
 When a soil is rich in nitrogen the gain from rain 
 and snow is only a partial restoration of that which 
 has been given off from the soil to the air or lost in the 
 drain waters. The principal forms of the nitrogen in 
 rain water are ammonium carbonate and nitrates and 
 nitrites, present in the air to the extent of about 22 parts 
 per million parts of air. 
 
 143. — Ratio of Nitrogen to Carbon in the Organic 
 Matter of Soils. — In some soils the organic matter is 
 more nitrogenous than in others. In those of the arid 
 regions the humus contains from 15 to 20 per cent of 
 
132 SOILS AND FERTILIZERS 
 
 nitrogen, while in soils from the humid regions there is 
 from 4 to 6 per cent.*^ In some soils the ratio of nitro- 
 gen to carbon is i to 6, while in others it may be i to 
 1 8, or more. That is, in the organic matter of some soils 
 there is i part of nitrogen to 6 parts of carbon, while in 
 others the organic matter contains i part of nitrogen to 
 1 8 parts of carbon. In a soil where there exists a wide 
 ratio between the nitrogen and carbon, it is believed the 
 conditions for supplying crops with available nitrogen 
 are unfavorable. 
 
 144. Losses of Nitrogen from Soils. — When a soil 
 rich in nitrogen is cultivated for a number of years ex- 
 clusively to grain, there is a loss of nitrogen exceeding 
 that removed in the crop, caused by the rapid oxida- 
 tion of the organic matter of the soil. Experiments 
 show that when a prairie soil of average fertility is 
 cultivated continually to grain, for every 25 pounds of 
 nitrogen removed in the crop there is a loss of about 
 150 pounds due to the destruction of the organic mat- 
 ter.!^ In general, any system of cropping which keeps 
 the soil continually under the plow results in decreas- 
 ing the nitrogen. When a soil is rich in nitrogen the 
 greatest losses occur; when poor in nitrogen there is 
 relatively less loss. When a soil rich in nitrogen is 
 given arable culture, oxidation of the organic matter and 
 losses of nitrogen take place rapidly. The longer a 
 soil is cultivated, the slower the oxidation of the humus \ 
 and relative loss of nitrogen. 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES 1 33 
 
 Dyer has calculated the income and outgo of ni- 
 trogen from manured and unmanured plots at the 
 Rothamsted Station for a period of fifty years. " Of 
 the total 10,000 pounds of nitrogen estimated to have 
 been supplied, then, we find (in round numbers) that 
 1600 pounds have been recovered in the increased 
 crops and that about 2500 pounds are found in the 
 surface soil, leaving 5900 (or, in round numbers, 
 6000) pounds to be accounted for otherwise. It is 
 clear, therefore, in spite of the notable surface ac- 
 cumulation, but little of the large quantities of nitrogen 
 supplied in the dung and ntot returned in crops is to 
 be found in the subsoil. The greater part of it has 
 disappeared either as nitrates in the drainage or per- 
 haps, and probably largely, by fermentative processes 
 yielding free nitrogen." ^^ 
 
 145. Gain of Nitrogen in Soils. — Lawes and Gilbert 
 found a gain of nitrogen when land was permanently 
 covered with vegetation."** Pastures and meadows 
 contain more than cultivated land of similar character. 
 
 Arable land . . 
 Barn-field pasture 
 Apple-tree pasture 
 Meadow . . . 
 Meadow . . . 
 
134 SOILS AND FERTILIZERS 
 
 After deducting the amount of nitrogen in the ma- 
 nure added to the meadow land, the annual gain of nitro- 
 gen was more than 44 pounds per acre. 
 
 If a soil is properly manured and cropped, the 
 nitrogen may be increased. A five-course rotation of 
 small grains, clover, and corn (manured) will generally 
 leave the soil at the end of the period of rotation in 
 better condition as regards nitrogen than at the be- 
 ginning. 
 
 At the Minnesota Experiment Station where wheat, 
 corn, barley, and oats were grown continuously for 
 twelve years, a loss of about 2000 pounds per acre of 
 nitrogen was sustained ; from | to |^ of the nitrogen be- 
 ing lost in various ways and not utilized as plant food.^^ 
 In experiments covering ten-year periods, it, was found 
 that the five-year rotations, in which clover formed an 
 essential part, resulted in a slight increase in the nitro- 
 gen content of the soil, — about 300 pounds per acre in 
 excess of that removed in the crops. When timothy 
 and non-legumes were substituted for clover, " a loss 
 of nitrogen from the soil occurred, but the carbon 
 (humus) content was maintained ; the loss of nitrogen 
 from the soil only slightly exceeding that removed by 
 the crops." ^^ 
 
 It is to be regretted that in the cultivation of large 
 areas of land to staple crops, as wheat, corn, and cotton, 
 the methods of cultivation followed are such as to de- 
 crease the nitrogen content and crop-producing power 
 of the soil when this might be prevented. 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES 1 35 
 
 NITRIFICATION 
 
 146. Former Views regarding Nitrification. — The 
 
 presence of nitrates and nitrites in soils was formerly 
 accounted for by oxidation. The theory was held that 
 the production of nascent nitrogen by the decomposition 
 of organic matter caused a union between the oxygen 
 of the air and the nitrogen of the organic matter. Fer- 
 mentation studies by Pasteur led him to suggest in 1862 
 that possibly the formation of nitric acid in the soil 
 might be due to fermentation. It was, however, fifteen 
 years later before the French chemists, Schlosing and 
 Miintz, established the fact that nitrification is pro- 
 duced by a living organism. They passed diluted sew- 
 age through a glass tube filled with sand to which a 
 little lime was added. The first portions of sewage 
 contained nitrogen in the form of ammonia, but after a 
 number of days nitrates appeared, and the ammonia 
 diminished. When the soil was treated with chloro- 
 form vapor, nitrates ceased to be formed ; when fresh 
 garden soil was added, nitrates again appeared in the 
 leachings. The bacteria were destroyed by the chloro- 
 form, and the medium was reseeded from the garden 
 soil. 
 
 147. Nitrification caused by Micro-organisms. — Nitri- 
 fication is the process by which nitrates and nitrites are 
 produced in soils by the workings of organisms. Nitri- 
 fication results in changing the complex organic nitro- 
 
136 
 
 SOILS AND FERTILIZERS 
 
 gen of the soil to the form of nitrates or nitrites. 
 Broadly speaking, it is the process by which the inert 
 nitrogen of the soil is rendered available as crop food. 
 The organisms which carry on the work of nitrification 
 were first isolated and studied by Winogradsky. 
 
 148. Conditions Necessary for Nitrification are : 
 
 1. Presence of the nitrifying organisms and food for 
 them. 
 
 2. A supply of oxygen. 
 
 3. Moisture. 
 
 4. A favorable temperature. 
 
 5. Absence of strong sunlight. 
 
 6. The presence of some basic compound. 
 
 In order to allow nitrification to proceed, all of these 
 conditions must be satisfied. The process is frequently 
 checked because some of the conditions, as presence of 
 a basic compound, are unfulfilled. 
 
 -», 
 
 
 tf 
 
 • 
 
 • • 
 
 • 
 
 
 • 
 
 9 ■;-■■ 
 
 <m 
 
 • 
 • 
 9 
 
 V 
 
 
 • 
 
 • 
 • 
 
 ,-■:■». ' 
 
 * 
 
 t 
 
 
 
 9 
 
 
 
 
 ?.9:-, 
 
 Qi 
 
 "^ 
 
 9 
 
 «„ - 
 
 
 
 m 
 
 
 
 
 ?? 
 
 ^ 
 
 9 
 
 » 
 
 f 
 
 
 • • • 
 
 • • « 
 
 '':"& 
 
 
 
 
 
 
 
 **^ 
 
 ife;L' 
 
 « 
 
 * 
 
 
 • 
 
 • • ♦• 
 
 '-,-'* 
 
 Fig. 32. Nitroub Acid Uigaiiisnis. (After Winogradsky.) 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES 1 3/ 
 
 149. Food for the Nitrifying Organisms. — All living 
 organisms require food, and one of the food require- 
 ments of the nitrifying organism is a supply of phos- 
 phates and other minerals. In the absence of phos- 
 phoric acid, nitrification cannot take place. The 
 change which the phosphoric acid undergoes in serving 
 
 Fig. 33. Nitric Acid Oiganism. (Alter Winogradsky ) 
 
 as food for the nitrifying organism is unknown, but it 
 doubtless makes the phosphoric acid more available as 
 plant food.^i The principal organic food of the nitrify- 
 ing organism is the organic matter of the soil, and it is 
 only when organic matter is incorporated with soil that 
 it can serve as food for the nitrifying organism. In the 
 presence of a large amount of organic matter, as in a 
 manure pile, nitrification does not take place. It occurs 
 only when the organic matter is largely diluted with 
 soil. Under favorable conditions, nitrifying organisms 
 
138 SOILS AND FERTILIZERS 
 
 may secure all of their food in inorganic forms ; that is, 
 nitrification may take place in the absence of organic 
 matter, provided the proper mineral food be supplied. 
 When growth under such conditions takes place the 
 organisms assimilate carbon from the combined carbon 
 of the air, and produce organic carbon compounds. An 
 organism, working in the absence of sunlight and un- 
 provided with chlorophyll, may construct organic com- 
 pounds containing nitrogen and designated bacterial 
 protein.** Nitrification in the absence of nitrogenous 
 organic matter is of too limited a character to supply 
 growing crops with all of their available nitrogen. For 
 general crop production the organic matter of the soil 
 is the source of the nitrogen which undergoes the nitri- 
 fication process, and which furnishes food for the nitrify- 
 ing organisms. 
 
 150. Oxygen Necessary for Nitrification. — The second 
 requirement for nitrification is an adequate supply of 
 oxygen. The nitrifying organism belongs to that class 
 of ferments (aerobic) which requires oxygen for exist- 
 ence. Oxygen is present as one of the elements in the 
 final product of nitrification as calcium nitrate, Ca(N03)2. 
 In the absence of oxygen, nitrification is checked. 
 When soils are saturated with water, the process can- 
 not go on for want of oxygen. The formation of a 
 hard, dry crust in soils also checks nitrification. Cultiva- 
 tion, particularly of clay soils, favors nitrification by 
 increasing the supply of oxygen in the soil. 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES 1 39 
 
 151. Moisture Necessary for Nitrification. — Nitrifica- 
 tion cannot take place in a soil deficient in moisture ; 
 as in all fermentation processes, moisture is necessary 
 for the chemical changes to occur. In a very dry time 
 nitrification is arrested for want of water. Water is as 
 necessary to the growth and development of the living 
 organism which carries on the work of nitrification as 
 it is to the life of a plant of higher order. 
 
 152. Temperatures Favorable for Nitrification. — The 
 
 most favorable temperatures for nitrification are between 
 12° C. (54° F.) and 37° C. (99° F.). It may take place 
 at as low a temperature as 3° or 4° C. (37° and 39° F); 
 at 50° C. (122° F.) it is feeble ; while at 55° C. (130° F.) 
 there is no action.** In northern latitudes nitrification 
 is checked during the winter, while in southern latitudes 
 this change takes place throughout the entire year. As 
 a result, many soils in southern latitudes contain less 
 nitrogen than soils in northern latitudes where forma- 
 tion and leaching of nitrates are checked by climatic 
 conditions. Crops which require their nitrogen early 
 in the growing season are frequently placed at a dis- 
 advantage because there is less available nitrogen in 
 the soil at that time than later. 
 
 153. Strong Sunlight checks Nitrification. — Nitrifica- 
 tion cannot take place in strong sunlight ; it prevents 
 the action of all organisms of this class. In fallow land 
 there is no nitrification at the surface, but immediately 
 
140 SOILS AND FERTILIZERS 
 
 below where the sunlight is excluded by the surface 
 soil it is most active. In a corn field it is more active 
 than in a compacted fallow field. 
 
 154. Base -forming Elements Essential for Nitrification. 
 
 — The presence of some base-forming element to com- 
 bine with the nitric acid produced is a necessary con- 
 dition for nitrification, and for this purpose calcium 
 carbonate and sodium and potassium compounds are 
 particularly valuable. The absence of alkaline salts is 
 one of the frequent causes of non-nitrification. In acid 
 soils the process is checked for the want of proper 
 basic material. The organisms which carry on the 
 work cannot exist where there are strong acids or 
 alkalies, consequently in such soils nitrification cannot 
 take place. 
 
 155. Nitrous Acid Organisms. — There are at least 
 two nitrifying organisms in the soil : one produces 
 nitrates and the other nitrites or nitrous acid. It has 
 been shown that the nitrification process takes place in 
 two stages : first nitrites are produced by the nitrous 
 organism, and then the process is completed by the 
 nitric organism. Warington says that " both organ- 
 isms are present in the soil in enormous numbers, and 
 the action of the two organisms proceeds together, as 
 the conditions are favorable to both." As a result 
 of the workings of the nitrous acid organism, nitrites 
 are formed, and these are acted upon by the nitric acid 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES I4I 
 
 organism and changed into nitrates. Nitrites exist in 
 soils as transition products, the amount present in fer- 
 tile soils being less than one part per million of soil. 
 
 156. Ammonia-producing Organisms. — There are also 
 present in the soil organisms which have the power 
 of producing ammonia from proteid bodies. The am- 
 monium compounds produced are acted upon by the 
 nitrifying organisms and readily undergo nitrifica- 
 tion.^^' ^^ When oxidation of the protein is rapid, nitro- 
 gen may be Hberated and lost. 
 
 157. Denitrification is just the reverse of the nitri- 
 fication process, and is the result of the workings of 
 a class of organisms which feed upon the nitrates, 
 forming free nitrogen which is liberated as a gas. One 
 of the conditions for denitrification is absence of air, 
 as these organisms belong to the anaerobic class. De- 
 nitrification occurs in soils saturated with water, and 
 where the soil is compacted so that air is practically 
 excluded.*'' ^^ 
 
 158. Number and Kinds of Organisms in Soils. — In 
 
 addition to the micro-organisms which carry on the 
 work of nitrification, denitrification, and ammonification, 
 there are a great many others, some of which are bene- 
 ficial while others are injurious to crop growth. It has 
 been estimated that in a gram of an average sample of 
 soil there are from 60,000 to 500,000 beneficial and 
 injurious micro-organisms.''^ There are produced from 
 
142 SOILS AND FERTILIZERS 
 
 many crop residues, by injurious ferments, chemical 
 products which may be destructive to crop growth. 
 Flax straw, for example, when it decays in the soil, 
 forms chemical products which are destructive to a 
 succeeding flax crop. 
 
 A moist soil, rich in organic matter, and containing 
 various salts, may form the medium for the propagation 
 of many classes of organisms. Sewage-sick soils, clover- 
 sick soils, and flax-diseased lands are all the result of 
 bacterial diseases. Many of the organisms which are 
 the cause of such diseases as typhoid fever and cholera 
 may propagate and develop in a moist soil under certain 
 conditions, and then find their way through drain water 
 into surface wells, and cause these diseases to spread. 
 
 159. Products formed by Soil Organisms. — In con- 
 sidering the part which micro-organisms take in plant 
 growth, as well as in all similar processes, there are two 
 important phases : (i) the action of the organism itself, 
 and (2) the chemical action of the product of the or- 
 ganism. In the case of nitrification, the action of the 
 organism brings about a change in the composition of 
 the organic matter of soils producing nitric acid, which 
 is merely a product formed as a result of the action of 
 the organism. The nitric acid then acts upon the soil, 
 producing nitrates. In soils rich in organic matter the 
 fermentation changes, which take place during humifi- 
 cation, result in the production of acid products. This 
 is simply the result of the action of the ferments. The 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES I43 
 
 acids then act upon the soil bases and produce humates 
 or organic salts. In many fermentation changes there 
 is first the production of some chemical compound, and 
 then the action of this compound upon other bodies. In 
 rendering plant food available, as in humification and 
 nitrification, it is the final and not the first product of 
 the organism, which is of value as plant food. 
 
 160. Inoculating Soils with Organisms. — In growing 
 leguminous crops on soils where they have never before 
 been produced, it has been proposed to supply the 
 essential organisms which assist the crops to obtain 
 their nitrogen. For example, if clover is grown on new 
 land, the soil may not contain the organisms which 
 assist in the assimilation of nitrogen and which are 
 present in the root nodules of the plant. If these 
 organisms are supplied, better conditions for growth 
 exist. Some soils are benefited by inoculation, while 
 others are not. Frequently the failure successfully to 
 grow legumes is due to other causes, as poor seed, poor 
 physical condition of the soil, lack of mineral plant 
 food, and adverse climatic conditions rather than to a 
 lack of the necessary nitrogen fixing-bacteria.^^ 
 
 In old soils where the process of nitrification is 
 feeble, it has been proposed to inoculate the soils with 
 more active forms of bacteria so as to make the inert 
 humus nitrogen more available as plant food. In order 
 to secure the best results from inoculation, suitable 
 food must be supplied for the organisms, and any ad- 
 
144 SOILS AND FERTILIZERS 
 
 verse condition, as excess of acids or alkalies, must 
 be corrected. Most soils contain the requisite organ- 
 isms, but frequently they are unable to do their work 
 because of unfavorable conditions, as the presence of 
 injurious matter or the lack of cultivation or food. 
 For the production of legumes, inoculation of the soil is 
 often beneficial. The commercial production and dis- 
 tribution of the organisms forming the nodules on the 
 roots of clover and other leguminous crops, and which 
 cause fixation of atmospheric nitrogen, was first pro- 
 posed and inaugurated by Nobbe.^* The method of in- 
 oculation consists in first multiplying the organisms 
 in nutritive substances, and then sprinkhng seeds with 
 the diluted solution. Inoculation with soil from a field 
 where clover or lupines have previously been grown has 
 also been successful, particularly in reclaiming sandy 
 waste lands where mineral fertilizers containing potash 
 and phosphates are used to furnish these elements, 
 while the more expensive nitrogen is acquired indirectly 
 from the air through the clover. Soils in a high state 
 of productiveness are not usually in need of inoculation 
 as they already contain all the essential soil organisms. 
 Moore's method of distributing the nitrogen-fixing organ- 
 isms of legumes in the form of cotton cultures has been 
 investigated by a number of experiment stations and 
 found inefficient.^'' 
 
 161. Loss of Nitrogen by Fallowing Rich Lands. — 
 
 Summer fallowing; creates conditions favorable to nitri- 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES I45 
 
 fication. A fallow is beneficial to a succeeding crop 
 because of the nitrogen which is rendered available. 
 If a soil is rich in nitrogen and lime, summer fallow- 
 ing causes the production of more nitrates than can be 
 retained in the soil. The crop utilizes only a part of 
 the nitrogen rendered available, the rest being lost by 
 drainage, ammonification, and denitrification. Hence 
 the available nitrogen is increased while the total nitro- 
 gen is greatly decreased.^ 
 
 Soil before 
 Fallowing 
 
 Soil after 
 Fallowing 
 
 Total nitrogen . 
 Soluble nitrogen 
 
 0.154 
 0.002 
 
 0.142 
 0.004 
 
 The gain of 0.002 per cent of soluble nitrogen was 
 accompanied by a loss of 0.012 per cent of total nitro- 
 gen. For every pound of available nitrogen there was 
 a loss of six pounds. Bare fallowing of land for an 
 entire year should not be practiced, except occasionally 
 to destroy weeds or insects, as it results in permanent 
 injury to the soil. A short period of fallow and the 
 practice of green manuring with leguminous crops both 
 enrich the soil with humus and nitrogen, and improve 
 the physical properties. 
 
 162. Influence of Plowing upon Nitrification, — In a 
 rich soil containing the necessary alkaline matter, nitrifi- 
 cation goes on very rapidly. This is one reason why 
 
146 SOILS AND FERTILIZERS 
 
 shallow plowing on new breaking gives better results 
 than deep plowing. Deep plowing at first causes nitri- 
 fication to take place to such an extent that the crop is 
 over-stimulated in growth, due to an excess of available 
 nitrogen. Deep plowing and thorough cultivation aid 
 nitrification. The longer a soil has been cultivated, the 
 deeper and more thorough must be the cultivation. 
 
 Early fall plowing leaves more available nitrogen at 
 the disposal of the crop than late fall plowing. Nitrifi- 
 cation takes place only near the surface. Hence when 
 late spring plowing is practiced there is brought to the 
 surface raw nitrogen, while the more active nitrogen has 
 been plowed under, and is beyond the reach of the young 
 plants when they require the most help in obtaining food. 
 The various methods of cultivation, as deep and shallow 
 plowing, spring and fall plowing, and surface cultivation, 
 have as much influence upon the available nitrogen 
 supply of crops as upon the water supply. The saying 
 that cultivation makes plant food available is particu- 
 larly true of the element nitrogen, the supply of which 
 is capable of being increased or decreased to a greater 
 extent than that of any other element. 
 
 NITROGENOUS MANURES 
 
 163. Sources of Nitrogenous Manures. — The materials 
 used for enriching soils with nitrogen, to promote crop 
 growth, may be divided into two classes: (i) organic 
 nitrogenous manures, (2) mineral nitrogenous manures. 
 
NITROGEN, NITRIFICATION,- NITROGENOUS MANURES 1 4/ 
 
 Each of these classes has a different vakie as plant 
 food, and in fact there are marked differences in fertili- 
 zer value between materials belonging to the same class. 
 The nitrogenous organic materials used for fertiUzing 
 purposes are : dried blood, tankage, meat scraps and 
 flesh meal, fish offal, cottonseed meal, and leguminous 
 crops, as clover and peas. The nitrogen in these sub- 
 stances is principally in the form of protein. When 
 peat and muck are properly used they also may be 
 classed among the nitrogenous manures. The mineral 
 nitrogenous manures are nitrates, as sodium nitrate, and 
 ammonium salts, as ammonium sulphate. 
 
 164. Dried Blood. — This is obtained by drying the 
 blood and debris from slaughterhouses. Frequently 
 small amounts of salt and slaked lime are mixed with 
 the blood. It is richest in nitrogen of any of the 
 organic manures. When thoroughly dry it may contain 
 14 per cent of nitrogen. As usually sold, it contains 
 from 10 to 20 per cent of water, and has a nitrogen 
 content of from 9 to 13. Dried blood contains only 
 small amounts of other fertilizer elements ; it is strictly 
 a nitrogenous fertilizer, readily yielding to the action of 
 micro-organisms and to nitrification. On account of its 
 fermentable nature, it is a quick-acting fertilizer, and is 
 one of the most valuable of the organic materials used as 
 manure. It gives the best returns on an impoverished 
 soil to aid crops in the early stages of growth, before 
 the inert nitrogen of the soil becomes available. Dried 
 
148 SOILS AND FERTILIZERS 
 
 blood may be applied as a top dressing on grass land, 
 and it is also an excellent form of fertilizer for many 
 garden crops ; but it should not be placed in direct con- 
 tact with seeds, as it will cause rotting, nor should it be 
 used in too large amounts. Three hundred pounds per 
 acre is as much as should be appHed at one time. When 
 too much is used losses of nitrogen may occur by leach- 
 ing and by denitrification. It is best applied directly to 
 the soil as a top dressing in the case of grass, or near 
 the seeds of garden crops, and not mixed with unslaked 
 lime or wood ashes, but each should be used separately. 
 As all plants take up their nitrogen in the early stages 
 of growth, nitrogenous fertilizers as blood should be ap- 
 plied before seeding or soon after. An application of 
 dried blood to partially matured garden crops will cause 
 a prolonged growth and very late maturity. 
 
 Storer gives the following directions for preserving 
 any dried blood produced upon farms.^^ " The blood 
 is thoroughly mixed in a shallow box with 4 or 5 times 
 its weight of slaked lime. The mixture is covered with 
 a thin layer of lime and left to dry out. It will keep if 
 stored in a cool place, and may be applied directly to 
 the land or added to a compost heap." 
 
 The price per pound of nitrogen in the form of dried 
 blood can be determined from the cost and the analysis 
 of the material. A sample containing 9 per cent of nitro- 
 gen and selling for $28 per ton is equivalent to 15-55 
 cents per pound for the nitrogen (2000x0.09=180. 
 ).oo-7- 180= 15.55 cents). 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES I49 
 
 165. Tankage is composed of refuse matter, as bones, 
 trimmings of hides, hair, horns, hoofs, and some blood. 
 The fat and gelatin are, as a rule, first removed by sub- 
 jecting the material to superheated steam. This mis- 
 cellaneous refuse, after drying, is ground and some- 
 times mixed with a little slaked lime to prevent rapid 
 fermentation. 
 
 Tankage contains less nitrogen but more phosphoric 
 acid than dried blood. Owing to its miscellaneous na- 
 ture, it is quite variable in composition, as the following 
 analyses of tankage from the same abattoir at different 
 times show : ^* 
 
 Moisture 
 Nitrogen 
 Phosphoric acid 
 
 per cent 
 
 First 
 Year 
 
 10.5 
 
 5-7 
 12.2 
 
 Second 
 Year 
 
 9.8 
 
 7.6 
 
 10.6 
 
 Third 
 
 Year 
 
 10.9 
 
 6.4 
 
 II.7 
 
 As a general rule, tankage contains from 5 to 8 per 
 cent of nitrogen and from 5 to 12 per cent of phos- 
 phoric acid. It is much slower in its action than dried 
 blood, and supplies the crop with both nitrogen and 
 phosphoric acid. Tankage is a valuable form of fer- 
 tilizer for garden purposes. It may also be used as 
 a top dressing on grass lands, or spread broadcast on 
 grain lands. It is best to apply the tankage, when pos- 
 sible, a few days prior to seeding, and it should not 
 come in contact with seeds. Two hundred and fifty 
 
150 SOILS AND FERTILIZERS 
 
 pounds per acre is a safe dressing, and when there is 
 sufficient rain to ferment the tankage, 400 pounds per 
 acre may be used. A dressing of 800 pounds in a dry 
 season would be destructive to vegetation. On impov- 
 erished soil more may be used than on soils which are 
 for various reasons out of condition. The cost of the 
 nitrogen as tankage is determined from the composi- 
 tion and selling price. If tankage containing 7 per 
 cent of nitrogen and 12 per cent of phosphoric acid is 
 selling for $32 per ton, what is the cost of the nitrogen 
 per pound ? The market value of phosphoric acid, in 
 the form of bones, should first be ascertained. Sup- 
 pose bone phosphoric acid is selling for 4 cents per 
 pound. The phosphoric acid in the ton of tankage 
 would then be worth 1^9.60, making the nitrogen cost 
 ^22.40. The 140 pounds of nitrogen in the ton of fer- 
 tilizer would be worth $22.40, or 16 cents per pound. 
 In eastern markets the price of tankage is usually higher 
 than near the large packing houses of the West. 
 
 166. Flesh Meal. — The flesh refuse from slaughter- 
 houses is sometimes kept separate from the tankage 
 and sold as flesh meal, the fat and gelatin being first 
 removed and used for the manufacture of glue and 
 soap. Flesh meal is variable in composition and may 
 be very slow in decomposing. It contains from 4 to 8 
 per cent or more of nitrogen, with an appreciable amount 
 of phosphoric acid. Occasionally it is used for feeding 
 poultry and hogs, and cattle to a limited extent. The 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES I5I 
 
 fertilizer value of the dung is nearly equivalent to the 
 original value of the meal. 
 
 167. Fish Scrap. — The flesh of fish is very rich in 
 nitrogen."*^ The offal parts, as heads, fins, tails, and intes- 
 tines, are dried and prepared as a fertilizer. Some species 
 of fish which are not edible are caught in large numbers 
 to be used for this purpose. In seacoast regions, fish fer- 
 tilizer is one of the cheapest and best of the nitrogenous 
 manures. It is richer in nitrogen than tankage or flesh 
 meal, and in many cases equal to dried blood. It read- 
 ily undergoes nitrification and is a quick-acting fertilizer. 
 
 168. Seed Residues. — Many seeds, as cottonseed and 
 flaxseed, are exceedingly rich in nitrogen. When the oil 
 has been removed, the flaxseed and cottonseed cake are 
 proportionally richer in nitrogen than the original seed. 
 This cake is usually sold for cattle food, but occasionally 
 is used as fertiUzer. It contains from 6 to 7 per cent of 
 nitrogen, and compares fairly well in nitrogen content 
 with animal bodies. Cottonseed cake and meal are not 
 
 i so quick acting as dried blood, but when used in south- 
 
 ] em latitudes a Httle time before seeding, the nitrogen 
 
 { becomes available for crop purposes. Oil meals, as 
 
 j cottonseed and linseed, containing a high per cent of 
 
 ( oil, are much slower in decomposing than those which 
 
 i contain but little oil. It is better economy to feed the 
 
 i cake to stock and use the manure than to apply the cake 
 
 : directly to the land. Occasionally, however, cottonseed 
 
152 SOILS AND FERTILIZERS 
 
 meal has been so low in price that its use as a fertilizer 
 has been admissible. 
 
 A ton of cottonseed meal, costing $20 and containing 
 2 per cent of phosphoric acid and 7 per cent of nitro- 
 gen, would be equivalent to 13.1 cents per pound for 
 the nitrogen, which is frequently cheaper than purchas- 
 ing some other nitrogenous fertilizer. 
 
 169. Leather, Wool Waste, and Hair are rich in nitro- 
 gen, but on account of their slowness in decomposing 
 are unsuitable for fertilizer purposes. When present in 
 fertilizers they give poor field results. 
 
 170. Available Nitrogen. — One of the methods em- 
 ployed to detect, in fertilizers, the presence of inert 
 forms of nitrogen, as leather, is to digest the material in 
 prepared pepsin solution. ^*^ Substances like dried blood 
 are nearly all soluble in the pepsin, while leather and other 
 inert forms are only partially so. The solubihty of the 
 organic nitrogen in pepsin solution determines, to a great 
 extent, the value of the material as a fertilizer.^^ 
 
 Dried blood . . . 
 Cottonseed meal 
 Ground dried fish . 
 Tankage .... 
 Hoof and horn meal 
 Leather .... 
 
 Per Cent of Nitrogen 
 
 Soluble in Prepared 
 
 Pepsin Solution 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES 1 53 
 
 Some of the organic forms of nitrogen readily undergo 
 nitrification and become available as plant food, while 
 other forms are inactive. Vegetation tests show that 
 from 60 to 75 per cent of the nitrogen of dried blood, 
 tankage, cottonseed meal, and fish meal are available as 
 plant food the year they are used as fertilizer. The 
 available nitrogen of fertilizers includes nitrates and 
 ammonium salts and such forms of organic matter as 
 readily undergo nitrification. Potassium permanganate 
 with and without sodium hydroxide is also employed 
 as a solvent for available nitrogen. ^^ 
 
 171. Peat and Muck. — Peat and muck are rich in 
 nitrogen which is in an insoluble form and is with diffi- 
 culty nitrified. When mixed with lime and stable 
 manure, particularly liquid manure, fermentation is 
 induced and a valuable manure produced. Muck and 
 peat should be dried and sun-cured, and then used as 
 absorbents in stables. Peat differs from muck in being 
 fibrous. If the muck is acid, lime (not quicklime) should 
 be used with it in the stable, as directed under farm 
 manures. When easily obtained, muck is one of the 
 cheapest forms of nitrogen. 
 
 Composition of Dry Muck Samples^ 
 
 Nitrogen 
 Per Cent 
 
 Marshy place, producing hay 
 Marshy place, dry in late summer 
 Old lake bottom 
 
 2.21 
 2.01 
 1.81 
 
154 SOILS AND FERTILIZERS 
 
 172. Leguminous Crops as Nitrogenous Manures. — 
 The frequent use of leguminous crops for manurial pur- 
 poses is the cheapest way of obtaining nitrogen. When 
 the crop is not removed from the land but is plowed 
 under while green, the practice is called green manur- 
 ing. This does not enrich the land with any mineral 
 material, but results in changing inert plant food to 
 humate forms. Green manuring with leguminous crops 
 should take the place of bare fallow, as its effects upon 
 the soil are more beneficial. With green manuring, 
 nitrogen is added to the soil, while with bare fallow there 
 is a loss of nitrogen. Leguminous crops, as clover, peas, 
 crimson clover, and cowpeas, should be made to serve 
 as the main source of the nitrogen for crop production. 
 A good crop of clover will return to the soil over 200 
 pounds of nitrogen per acre. 
 
 173. Sodium Nitrate. — The nitric nitrogen most 
 frequently met with in commercial forms is sodium 
 nitrate, commonly known as Chili saltpeter. It is a 
 natural deposit found extensively in Chili, Peru, and 
 the United States of Colombia. Various theories have 
 been proposed to account for these deposits, but it is 
 difficult to determine just how they have been formed.^*' 
 The commercial value of nitrogen in fertilizers is regu- 
 lated mainly by the price of sodium nitrate, which, when 
 pure, contains 16.49 P^^ cent of nitrogen. Commer- 
 cial sodium nitrate is from 95 to 97 per cent pure. 
 An ordinary sample contains about 16 per cent of 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES 1 55 
 
 nitrogen and costs from $50 to $60 per ton, making 
 the nitrogen worth from 15 to 18 cents per pound. 
 Sodium nitrate is the most active of all the nitrogenous 
 manures. It is soluble and does not have to undergo 
 the nitrification process before being utilized by crops. 
 On account of its extreme solubility it should be ap- 
 plied sparingly, for it cannot be retained in the soil. 
 As a top dressing on grass, it will respond by impart- 
 ing a rich green color. It may be used at the rate of 
 250 pounds per acre, but a much lighter application will 
 generally be found more economical. Sodium nitrate 
 should not be used when heavy dressings of farm 
 manure are appHed, as denitrification may result from 
 such a practice. In small amounts it is the fertilizer 
 most frequently resorted to when the forcing of crops 
 is desired, as in early market gardening. Its use for 
 fertilizing horticultural crops has become equally as ex- 
 tensive as for general farm crops. Excessive amounts, 
 however, may produce injurious results. Sodium nitrate 
 stimulates a rank growth of dark green foliage and 
 retards the maturity of plants, but when properly used 
 is one of the most valuable of the nitrogenous ferti- 
 lizers. 
 
 174. Ammonium Sulphate. — Ammonium sulphate is 
 obtained as a by-product in the manufacture of illu- 
 minating gas and is extensively sold as a fertilizer. It 
 usually contains about 20 per cent of nitrogen, equiv- 
 alent to 95 per cent of ammonium sulphate, the re- 
 
156 SOILS AND FERTILIZERS 
 
 maining 5 per cent being moisture and impurities. 
 Ammonium sulphate is not generally considered the 
 equivalent of sodium nitrate, as it is believed it must 
 undergo nitrification before being utilized as plant 
 food. It is, however, a valuable form of nitrogen. Ex- 
 periments show that plants may utilize ammonia directly 
 without nitrification processes first taking place.'^^ The 
 statements regarding the use of sodium nitrate apply 
 equally well to the use of ammonium sulphate. Am- 
 monium chloride and ammonium carbonate are not 
 suitable for fertilizers on account of their destructive 
 action upon vegetation. 
 
 175. Calcium Nitrate and Cyanamid, Ca(N03).2 and 
 CaCNg. — The nitrogen of these compounds is obtained 
 from the free nitrogen of the air by electrical processes. 
 Calcium nitrate is made by treating Hme with nitric acid 
 resulting from the oxides of nitrogen produced in the 
 air by electrical action. It is a valuable form of nitrogen 
 fertilizer. Calcium cyanamid is made by heating together 
 coal and lime in an electrical furnace through which a 
 current of nitrogen gas, obtained from the air, is passed. 
 Experiments with calcium cyanamid as a fertilizer show 
 that the nitrogen undergoes nitrification and becomes 
 available as plant food.^^ It is claimed that these com- 
 pounds of nitrogen Ca(N03)2 and CaCN2, in which the 
 nitrogen is obtained from the air, will eventually be pro- 
 duced at such a low cost as to permit their extensive use 
 as fertilizers. 
 
NITROGEN, NITRIFICATION, NITROGENOUS MANURES 1 5/ 
 
 176. Nitrogen and Ammonia Equivalent of Fertilizers. 
 
 — Nitrogenous fertilizers are sometimes represented 
 as containing a certain amount of ammonia instead of 
 nitrogen. Fourteen-seventeenths of ammonia is nitro- 
 gen, and if a fertilizer contains 2.25 per cent ammonia, 
 it is equivalent to 1.85 per cent of nitrogen. To convert 
 NHg results to an N basis, multiply by 0.823. 
 
 177. Purchasing Nitrogenous Manures. — In purchas- 
 ing a nitrogenous manure, the special purpose for which 
 it is to be used should always be considered. Under 
 some conditions, as forcing a crop on an impoverished 
 soil, sodium nitrate is desirable. Under other conditions, 
 tankage, cottonseed cake, or some other form of nitro- 
 gen may be better. There is annually expended in pur- 
 chasing nitrogenous fertilizers a large amount of money 
 which could be expended more economically if the 
 science of fertilizing were given a more careful study, 
 and if a larger share of the nitrogen for crop pur- 
 poses were obtained indirectly from the air through the 
 agency of legumes. The uses of nitrogenous fertilizers 
 for special crops and the testing of soils to determine 
 any deficiency in nitrogen are discussed in Chapters 
 X and XI, which treat of commercial fertilizers and the 
 food requirements of farm crops. 
 
CHAPTER V 
 
 FARM MANURES 
 
 178. Variable Composition of Farm Manures. — The 
 term ' farm manure ' does not designate a product of 
 definite composition. Manure is the most variable in 
 chemical composition of any of the materials produced 
 on the farm. It may contain a large amount of straw, 
 in which case it is called coarse manure ; or it may con- 
 tain only the soUd excrements and a little straw, the 
 liquid excrements being lost by leaching ; then again 
 it may consist of the droppings of poorly fed animals, 
 or of the mixed excrements of different classes of well- 
 fed animals. 
 
 The term * stable manure ' has been proposed for that 
 product which contains all of the solid and liquid excre- 
 ments with the necessary absorbent, before any losses 
 have been sustained. ^^ The term 'barnyard manure' is 
 restricted to that which accumulates around some barns 
 and farmyards, and is exposed to leaching rains and the 
 drying action of the sun. 
 
 179. Average Composition of Manures. — The soHd 
 excrements of animals contain from 60 to 85 per cent 
 of water ; when mixed with straw, and the liquid ex- 
 crements are retained, the mixed manure contains 
 
 158 
 
FARM MANURES 
 
 159 
 
 about 75 per cent of water. The nitrogen varies from 
 0.4 to 0.9 per cent, 'according to the nature of the food 
 and the extent to which other factors have affected the 
 composition. In general, animals consuming liberal 
 
 -4. 2.1:3. 
 
 Fig. 34. Average Composition of Fresh 
 
 Manure. 
 
 I. Nitrogen. 2. Phosphoric acid. 
 
 3. Potash. 4. Mineral matter. 
 
 Fig. 35. Manure after Six 
 Months' Exposure. 
 
 amounts of coarse fodders produce manure with a 
 higher per cent of potash than of phosphoric acid. 
 This is because the potash in the food exceeds the 
 phosphoric acid. Farm manures also contain lime, 
 magnesia, and other minerals present in plants and 
 designated as essential ash elements. The average 
 composition of mixed stable manure is as follows : 
 
 Nitrogen, N . . . 
 Phosphoric acid, P^O^ 
 Potash, K„0 . . . 
 
 Average 
 Per Cent 
 
 0.50 
 
 0-35 
 0.50 
 
 Range 
 Per Cent 
 
 0.4 to 0.8 
 0.2 to 0.5 
 0.3 to 0.9 
 
i6o 
 
 SOILS AND FERTILIZERS 
 
 In calculating the amount of fertility in manures, it 
 is more accurate to compute the value from the food 
 consumed and the conditions under which the manure 
 has been produced, than to use figures expressing aver- 
 age composition. 
 
 180. Factors which influence the Composition and 
 Value of Farm Manure. — 
 
 I. Kind and amount of absorbents used. 
 11. Kind and amount of food consumed. 
 
 III. Age and kind of animals. 
 
 IV. Methods employed in collecting, preserving, and 
 utilizing the manure. 
 
 Any one of the above, as well as many minor fac- 
 tors, may influence the composition and value of farm 
 manures. 
 
 181. Absorbents. — The absorbent generally used is 
 straw. Wheat straw and barley straw have about the 
 same manurial value ; oat straw is more valuable than 
 either. The average composition of straw and other 
 absorbents is as follows : 
 
 Nitrogen . . . 
 Phosphoric acid 
 Potash . . . . 
 
 Straw 
 Per Cent 
 
 0.40 
 0.36 
 0.80 
 
 Leaves 
 Per Cent 
 
 0.6 
 
 0-3 
 0-3 
 
 Peat 
 Per Cent 
 
 Sawdust 
 Per Cent 
 
 O.I 
 0.2 
 0.4 
 
 When a large amount of straw is used the percentage 
 amounts of nitrogen and phosphoric acid are decreased, 
 
FARM MANURES l6l 
 
 while the per cent of potash is slightly increased. Saw- 
 dust and loam both make the manure more dilute. Dry- 
 peat makes the. manure richer in nitrogen. The ab- 
 sorptive power of these different materials is about as 
 follows : 1* 
 
 Per Cent of 
 Water Absorbed 
 
 Fine cut straw 
 Coarse uncut straw 
 
 Peat 
 
 Sawdust .... 
 
 30.0 
 18.0 
 60.0 
 
 45.0 
 
 The proportion of absorbents in manure ranges from 
 a fifth to a third of the total weight of the manure. 
 
 182. Use of Peat and Muck as Absorbents. — Because 
 
 of the high content of nitrogen in peat and the power 
 which it possesses when dry of absorbing water, it is 
 a valuable material to use as an absorbent in stables. 
 As previously stated, peat is slow to decompose, but 
 when mixed with the liquid manure it readily yields to 
 fermentation, particularly if a Httle land plaster or marl 
 be used in the stable along with the peat. Peat has 
 high absorptive power for gases as well as for liquids, 
 and when used the sanitary condition of stables is im- 
 proved and the air is rendered particularly free from 
 foul odors. 
 
l62 
 
 SOILS AND FERTILIZERS 
 
 RELATION OF FOOD CONSUMED TO MANURE PRODUCED 
 
 183. Bulky and Concentrated Foods. -r- The more con- 
 centrated and digestible the food consumed, the more 
 valuable is the manure. Coarse bulky fodders always 
 give a large amount of a poor quality of manure. For 
 example, the manure from animals fed on timothy hay 
 and that from animals fed on clover hay and grain 
 show a wide difference in composition. The dry matter 
 of timothy hay is about 55 per cent digestible. From 
 a ton of timothy hay there is about 790 pounds of dry 
 matter in the manure. The nitrogen, phosphoric acid, 
 and potash in the food consumed are nearly all returned 
 in the manure, except under those conditions which will 
 be noted. The manure from a ton of mixed feed, as 
 clover and bran, is smaller in amount but more concen- 
 trated than that produced from timothy. In a ton of 
 timothy and in a ton of mixed feed (1500 lbs. clover, 
 500 lbs. bran) there are present: 
 
 Timothy 
 Lbs. 
 
 Mixed Feed 
 Lbs. 
 
 Nitrogen . . 
 Phosphoric acid 
 Potash . . . 
 
 25.0 
 
 9.0 
 
 40.0 
 
 40.0 
 24.0 
 30.0 
 
 The nitrogen, phosphoric acid, and potash of these 
 two rations are retained in the animal body in dissimi- 
 lar amounts, 10 per cent more of these elements being 
 
FARM MANURES I63 
 
 retained from the more liberal ration, due to more 
 favorable conditions for growth. Because of this fact 
 there is present in the manure from the mixed feed one 
 half more nitrogen, and two and one half times as much 
 phosphoric acid, as in the manure from the timothy 
 hay, which, free from bedding, contains about 790 
 pounds of indigestible matter, while the manure from 
 the mixed feed contains 760 pounds, the mixed ration 
 being more digestible. If both manures contain the 
 same amount of absorbents, the manure from the ton 
 of mixed clover and bran will weigh slightly less, 
 but contain more fertility than that from the timothy 
 hay. 
 
 The value of manure can be accurately determined 
 from the composition of the food consumed and the 
 care which the manure has received. Only a small 
 amount of the nitrogen in the food is permanently 
 retained in the body. The larger portion is used for 
 repair purposes, the nitrogen of the tissues which 
 have been renewed being voided as urea in the 
 liquid excrements. Some of the nitrogenous com- 
 pounds of the food are utilized for the production 
 of fat, in which case the nitrogen is voided in the 
 excrements. The fact that but little of the nitrogen 
 and mineral matter of the food, under most condi- 
 tions, is retained in the body is shown by the in- 
 vestigations of Lawes and Gilbert upon the compo- 
 sition of the flesh added to animals while undergoing 
 the fattening process.^^ 
 
164 
 
 SOILS AND FERTILIZERS 
 
 Increase during Fattening 
 
 
 Water 
 
 Dry 
 
 Matter 
 
 Fat 
 
 Nitrogenous 
 Matter 
 
 Ash 
 
 Ox 
 
 Sheep .... 
 Pig .... 
 
 24.6 
 20.1 
 22.0 
 
 75-4 
 
 79-9 
 78.0 
 
 66.2 
 70.4 
 
 71-5 
 
 7.69 
 
 7-13 
 6.44 
 
 1.47 
 2.^6 
 0.06 
 
 The results of numerous digestion experiments show 
 that when the food undergoes digestion only from 5 
 to 15 per cent of the nitrogen is, as a rule, retained 
 in the body. The nitrogen of the food is utilized 
 largely to replace that which has been required for 
 vital functions ; it enters the body, undergoes digestion 
 changes, is utilized for some vital function, and is then 
 voided in the excrements. 
 
 The digestion of food has been compared to the 
 combustion of fuel : the undigested products of the 
 solid excrements represent the ashes, and the urine 
 represents the volatile products. When wood is burned 
 the nitrogen is converted into volatile products. When 
 food is digested and utilized by the body the digestible 
 nitrogen is mainly converted into urea, while the indi- 
 gestible nitrogen is voided in the dung. In the solid 
 and liquid excrements of animals from 80 to 95 per 
 cent of the nitrogen, phosphoric acid, and potash of the 
 food consumed is present. t. 
 
 184. Comparative Composition of Solid and Liquid Ex- 
 crements. — In composition the liquid excrements differ 
 
FARM MANURES 
 
 165 
 
 from the solids in having a much larger amount of 
 nitrogen and less phosphoric acid.^ 
 
 
 Water 
 
 Nitrogen 
 
 Phosphoric Acid 
 
 Potash 
 
 
 a 
 
 -a " 
 
 u 
 CAIPh 
 
 '3 " 
 
 JfL, 
 
 c 
 
 U) C 
 -O V 
 
 '3 " 
 
 .H"S 
 
 P Solids 
 ^ Per cent 
 
 •a u 
 '3 " 
 
 .2-5 
 
 c 
 
 ■3 S 
 
 Cows . . 
 
 76 
 
 89.0 
 
 0.50 
 
 1.20 
 
 
 0.30 
 
 Horses . 
 
 84 
 
 92.0 
 
 0.30 
 
 0.86 
 
 0.25 
 
 
 O.IO 
 
 Pigs . . 
 
 80 
 
 97.0 
 
 0.60 
 
 0.80 
 
 0.45 
 
 0.12 
 
 0.50 
 
 Sheep 
 
 58 
 
 86.5 
 
 0.75 
 
 1.40 
 
 0.60 
 
 0.05 
 
 0.30 
 
 The nitrogen in the food consumed influences the 
 amount of water in the manure. As a rule, a highly- 
 concentrated nitrogenous ration produces a higher per 
 cent of water than a well-balanced ration. There is 
 but little phosphoric acid in the liquid excrements of 
 horses and cows, while that of sheep and swine contains 
 appreciable amounts. 
 
 The liquid manure is more constant both in compo- 
 sition and amount than the solid excrements. This 
 fact may be observed from the following table, which 
 gives the composition of the solid and liquid excre- 
 ments of hogs when fed on different amounts of 
 grain, ^" 
 
 The nitrogenous waste matter in the urine is nearly 
 the same whether an animal be gaining or losing in flesh, 
 and hence it is, the urine is more constant in composi- 
 tion and quantity than the solid excrements. 
 
1 66 
 
 SOILS AND FERTILIZERS 
 
 
 
 Solid 
 
 Liquid 
 
 
 Kind of Food Daily 
 
 Excrements 
 
 Excrements 
 
 Lbs. 
 
 c 
 
 3 
 o . 
 
 
 
 
 he u 
 u 
 
 i ^ 
 
 go; 
 
 1^ a(^ 
 
 9^ 
 
 Barley and shorts .... 
 
 8 
 
 0.57 
 
 0.72 
 
 2.05 
 
 0.06 
 
 6 
 
 Barley 
 
 4 
 
 043 
 
 0.70 
 
 2.06 
 
 0.16 
 
 5h 
 
 Corn and shorts .... 
 
 2.V 
 
 0.80 
 
 
 2.65 
 
 0.20 
 
 61 
 
 Corn 
 
 i| 
 
 0.82 
 
 0.89 
 
 2.05 
 
 0.29 
 
 (In each experiment the amount of liquid excrement was 4 pounds.) 
 
 The amount and composition of the solid excre- 
 ments vary with the amount and kind of food con- 
 sumed. If the food is indigestible, the solid excrements 
 contain a larger part of the nitrogen as indigestible 
 protein. When an animal is supplied with the proper 
 food for all purposes, normal conditions exist, and the 
 amount of nitrogen voided in the liquid and solid 
 excrements is equal to that supplied in the food con- 
 sumed, except in the case of growing and milk-pro- 
 ducing animals. 
 
 Experiments at the Rothamsted Station show that 
 from 57 to 79 per cent of the total nitrogen in the 
 food of farm animals is voided in the liquid excrements, 
 and from 16 to 22 per cent is voided in the solids. 
 Nearly all of the mineral elements of the food are 
 voided in the excrements, less than 4 per cent being 
 
FARM MANURES 
 
 167 
 
 retained in the body; in the case of milk cows about 10 
 per cent of the ash of the food is recovered in the milk. 
 
 185. Manurial Value of Foods. — The manurial value 
 of a fodder is determined from the amount and com- 
 mercial value of the nitrogen, phosphoric acid, and 
 potash present in the fodder. A ton of clover hay, for 
 example, contains 35 pounds of nitrogen, 14 pounds of 
 
 Timothy hay . 
 Clover hay . 
 Wheat straw 
 Oat straw . . 
 Wheat . . . 
 Oats .... 
 Barley .... 
 Rye .... 
 Flax .... 
 Corn .... 
 Wheat shorts . 
 Wheat bran 
 Linseed meal . 
 Cottonseed meal 
 Milk .... 
 Cheese 
 
 Live cattle . . 
 Potatoes . . . 
 Butter . . . 
 Live pigs . . 
 
 Nitrogen 
 
 N 
 
 Lbs. 
 
 25 
 
 35 
 1 1 
 12 
 45 
 33 
 40 
 42 
 87 
 - 32 
 48 
 
 54 
 100 
 
 130 
 
 ID 
 90 
 
 53 
 7 
 I 
 
 40 
 
 Phosphoric Acid 
 P2O5 
 Lbs. 
 
 9 
 
 14 
 
 4 
 
 4 
 
 20 
 
 16 
 
 18 
 
 20 
 
 32 
 
 14 
 
 31 
 
 52 
 
 35 
 
 35 
 
 3 
 
 23 
 
 37 
 
 3 
 
 I 
 
 17 
 
 Potash 
 K,0 
 Lbs. 
 
 40 
 
 30 
 12 
 18 
 12 
 II 
 II 
 13 
 14 
 
 30 
 25 
 56 
 
 3 
 5 
 3 
 II 
 I 
 3 
 
l68 SOILS AND FERTILIZERS 
 
 phosphoric acid, and 30 pounds of potash. When the 
 nitrogen is worth 16 cents per pound, the phosphoric 
 acid 6 cents, and the potash 5 cents, the clover hay has 
 a manurial value of 1^7.94 per ton, Lawes and Gilbert 
 estimate that 80 per cent of the fertility in fodders is, 
 as a rule, returned in the manure. 
 
 In the preceding table are given the pounds of nitro- 
 gen, phosphoric acid, and potash per ton of some farm 
 products.^^ 
 
 186. Commercial Value of Manures. — When the value 
 of farm manure is calculated on the same basis as com- 
 mercial fertihzers, it will be found that stable manure 
 is worth from $2 to $3.50 per ton. The value of the 
 increased crops resulting from its use varies with con- 
 ditions. Farm manures favorably influence the yield of 
 crops for a number of years. As for example, a dress- 
 ing of 8 tons of manure will make average prairie land 
 yield upwards of 20 bushels per acre more corn the 
 first year, 5 bushels more wheat the second year, and 8 
 bushels or so more of other grains the third year, with 
 slightly increased yields in subsequent years, all due 
 to the original application of the manure. It is often 
 necessary to apply farm manure in order to secure a 
 stand of clover, which enriches the soil with nitrogen. It 
 sometimes takes from two to three years for the manure 
 entirely to repay the cost of its application. Its influence 
 is felt, however, for a much longer time. In calculating 
 the value of farm manure, the returns from its use for a 
 
FARM MANURES I 69 
 
 number of years must be considered and also its in- 
 fluence in permanently increasing the value of the land. 
 
 It is sometimes stated that the phosphoric acid and 
 potash in stable manure is not so soluble as that in 
 commercial fertilizers, and consequently is worth, less. 
 While not so soluble in the form of manure, it fre- 
 quently happens that the phosphoric acid and potash 
 in the commercial fertilizers become, through fixation 
 processes, less soluble when mixed with the soil than 
 the same elements in stable manure. 
 
 Stable manure is valuable not only for the fertiHty con- 
 tained but also because it makes the inert plant food of 
 the soil more available and exercises such a favorable in- 
 fluence on the water supply of crops ; hence it is justi- 
 fiable to assign the same, if not a higher, value to the 
 elements in well-prepared farm manures as to those in 
 commercial fertilizers. 
 
 INFLUENCE OF AGE AND KIND OF ANIMAL 
 
 187. Manure from Young and from Mature Animals. 
 
 — The manure from older animals is somewhat more 
 valuable than that from young animals, even when fed 
 the same kind of food. This is because more of the 
 phosphoric acid and nitrogen are retained in the body 
 of a young animal. It is not so much a difference in 
 digestive power as a difference in retentive power. In 
 older animals the proportion of new nitrogenous tissue 
 produced is much less than in young animals, and more 
 
170 SOILS AND FERTILIZERS 
 
 of the nitrogen of the food is used for repair purposes 
 and subsequently voided in the manure, while with 
 young animals more of the nitrogen is retained for the 
 construction of new muscular tissue. 
 
 When an animal is neither gaining nor losing in flesh, 
 and is not producing milk, an equihbrium is established 
 between the nitrogen in the food supply and the nitro- 
 gen in the manure, and practically all of the nitrogen 
 of the food is returned in the manure.^" 
 
 188. Cow Manure. — A milch cow when fed a bal- 
 anced ration will make from 60 to 70 pounds of solid 
 and liquid manure a day, of which 20 to 30 pounds are 
 liquid. The solid excrement contains about 6 pounds 
 of dry matter. When a cow is fed clover hay, corn 
 fodder, and grain, about half of the nitrogen of the food 
 is in the urine, about one fourth in the milk, and the re- 
 mainder in the solid excrement. Hence, if the solid 
 excrement only is collected, but a quarter of the nitro- 
 gen of the food is recovered; while if both solids and 
 liquids are utilized, three quarters of the nitrogen is 
 secured. Cow manure is extremely variable in compo- 
 sition and is the most bulky of any manure produced by 
 domestic animals. A well-fed cow will produce about 
 80 pounds of manure per day, including absorbents. 
 
 189. Horse Manure. — Horse manure contains less 
 water than cow manure, and is of a more fibrous na- 
 ture, doubtless due to the horse possessing less power 
 
FARM MANURES I7I 
 
 for digesting cellulose material. Horse manure readily 
 ferments and gives off ammonia products. When the 
 manure becomes dry, fire-fanging results, due to rapid 
 fermentation followed by the growth of fungous bodies, 
 and there is a heavy loss of nitrogen. Horse manure 
 is sometimes considered of but little value. This is 
 because it so readily deteriorates that when used it has 
 often lost much of its nitrogen by fermentation. When 
 mixed with cow manure, both are improved, the rapid 
 fermentation of the horse manure is checked, and at 
 the same time the cow manure is improved in texture. 
 It is estimated that horses void about three fifths of 
 their manure in the stable. A well-fed horse at ordi- 
 narily hard work produces 50 pounds per day, of 
 which about one fourth is urine. A horse produces 
 nearly 6 tons of manure per year in the stable. If 
 properly preserved and used, it is valuable and quick- 
 acting ; but if allowed to ferment and leach, it gives 
 poor results. 
 
 190. Sheep Manure. • — Sheep produce a small amount 
 of concentrated manure, containing less water than that 
 of any other domestic animal. It readily ferments and 
 is a quick-acting fertilizer. When combined with horse 
 and cow manure the mixture ferments more slowly. 
 Because of the small amount of water it contains, sheep 
 manure is very concentrated in composition. It is val- 
 uable for general gardening purposes and whenever a 
 concentrated, quick-acting manure is desired. 
 
1/2 SOILS AND FERTILIZERS 
 
 191. Hog Manure. — Hog manure is not constant in 
 composition on account of the varied character of the 
 food consumed. The manure from fattening hogs 
 which are well fed compares favorably in composition 
 and value with that produced by other animals. It 
 contains a high per cent of water, and, like cow ma- 
 nure, may be slow in decomposing. On account of 
 containing so much water, losses by leaching readily 
 occur. From a given weight of grain, pigs produce 
 less dry matter in the manure than do sheep or cows. 
 The liquid excrements of well-fed hogs are rich in ni- 
 trogen, containing, on an average, about 2 per cent. 
 The solids when leached, fermented, and deprived of 
 the liquid excrements have little value as fertilizer. 
 
 192. Hen Manure. — Like all other farm manures, 
 hen manure is variable in composition. The nitrogen 
 is mainly in the form of ammonium compounds, making 
 it a quick-acting fertilizer. When fowls are well fed 
 the manure contains about the same amount of nitro- 
 gen as that of sheep. Hen manure readily ferments 
 and if not properly cared for losses of nitrogen, as 
 ammonia, occur. It is not advisable to mix with it 
 hard wood ashes or ordinary lime, because the ammo- 
 nia is so readily liberated by alkaline compounds. The 
 value of hen manure is due to its being a quick-acting 
 fertiUzer rather than to its containing a large amount of 
 fertility. A hen produces about a bushel of manure 
 per year. 
 

 farm manures 
 Composition of Hen Manure 
 
 173 
 
 
 Per Cent 
 
 Water 
 
 57-50 
 1.27 
 0.82 
 
 Nitrogen 
 
 Phosphoric acid 
 Potash . . . 
 
 
 
 28 
 
 
 
 193. Mixing of Solid and Liquid Excrements. — The 
 
 solid and liquid excrements together make a well-bal- 
 anced manure. Urine alone is not a complete manure, 
 as it is deficient in phosphoric acid and other mineral 
 matter. The solid excrement and the urine, when 
 combined with soil, readily undergo nitrification. The 
 nitrogen in the solid excrement is in the form of indi- 
 gestible protein and is rendered available more slowly 
 as plant food. Land dressed with leached manure re- 
 ceives an unbalanced fertilizer deficient in nitrogen but 
 fairly well supplied with mineral matter and may fail to 
 respond because of the unbalanced character of the 
 manure. A large amount of fertility is often lost 
 through poor and leaky stable floors. When the floors 
 and trenches are made of cement, better sanitary condi- 
 tions prevail and losses of fertility are prevented. 
 The mixing of the solid and liquid excrements and 
 waste bedding should be accomplished in the stable 
 trenches. 
 
 194. Volatile Products from Manure. — Fermentation 
 of manure in stables results in the production of a large 
 
174 SOILS AND FERTILIZERS 
 
 number of volatile compounds and in loss of manurial 
 value. When urea ferments, ammonium carbonate, a 
 volatile product, results ; and where the proteids of ma- 
 nure ferment, ammonia is formed, which combines with 
 the carbon dioxide, always present in stables in Uberal 
 amounts as a product of respiration, to form ammonium 
 carbonate, a volatile compound. When the stable at- 
 mosphere becomes charged with ammonium carbonate, 
 some of it is deposited on the walls of the stable, 
 forming a white coating. The white coating found 
 on harnesses and carriages stored in poorly ventilated 
 stables is ammonium carbonate. Accumulations of 
 manure in the stable and poor ventilation are the condi- 
 tions favorable to its production. 
 
 195. Human Excrements. — The use of human excre- 
 ments as manure is sometimes advised, and in some 
 countries they are extensively so utilized. When fresh, 
 they may contain a high per cent of nitrogen and phos- 
 phoric acid ; but when fermented, a loss of nitrogen has 
 occurred. Heiden estimates looo pounds a year of 
 excrements per person, containing $2.25 worth of fertil- 
 ity.^^ For sanitary reasons, human excrements should 
 be used as manure with great care, and it is doubtful, 
 with the abundance and cheapness of plant food, 
 whether the practice is advisable. About 1840 Leibig 
 expressed tbe fear that the essential elements of plant 
 food would accumulate in the vicinity of large cities and 
 be wasted, and that in time there would be a decline in 
 
FARM MANURES 
 
 175 
 
 fertility due to this cause.^*^ Many political economists 
 shared the same fear. Since that time the fixation of 
 atmospheric nitrogen through the agency of leguminous 
 crops has been discovered, extensive beds of sodium 
 nitrate, phosphate rock, and Stassfurt salts have been 
 utilized, and larger areas of more fertile soil have been 
 brought under cultivation, so that it is not now so 
 essential to devise means for utilizing human excre- 
 ments as manure. 
 
 THE PRESERVATION OF MANURE 
 
 196. Leaching. — Leaching of manure is the greatest 
 source of loss. Experiments by Roberts show that 
 when horse manure is thrown in a loose pile and sub- 
 jected to the joint action of leaching and weathering it 
 may lose in six months nearly 60 per cent of its most 
 valuable fertiHzing constituents. The results of these 
 experiments are tabulated as follows: ^^ 
 
 Gross weight 
 Nitrogen . . 
 Phosphoric acid 
 Potash . . . 
 Value per ton 
 
 April 25 
 Lbs. 
 
 4000.00 
 19.60 
 14.80 
 36.00 
 
 Sept. 28 
 Lbs. 
 
 1730.00 
 
 7-79 
 
 7-79 
 
 8.65 
 
 $1.06 
 
 Loss 
 Per Cent 
 
 57 
 60 
 
 47 
 76 
 
 Cow manure, on account of its more compact nature, 
 does not leach so readily as horse manure. A similar 
 
176 
 
 SOILS AND FERTILIZERS 
 
 experiment with cow manure, conducted at the same 
 time, showed the following losses : 
 
 April 25 
 
 Sept. 28 
 
 Loss 
 
 Lbs. 
 
 Lbs. 
 
 Per Cent 
 
 10,000 
 
 5 
 
 [25 
 
 49 
 
 47 
 
 
 28 
 
 41 
 
 32 
 
 
 26 
 
 19 
 
 48 
 
 
 44 
 
 8 
 
 $2.29 
 
 $1 
 
 .60 
 
 — 
 
 Gross weight . 
 Nitrogen . . 
 Phosphoric acid 
 Potash . . . 
 Value per ton 
 
 When mixed cow and horse manure was compacted 
 and " placed in a galvanized iron pan with a perforated 
 bottom " for six months, the losses were as follows : 
 
 
 March 29 
 
 Sept. 30 
 
 Loss 
 
 
 Lbs. 
 
 Lbs. 
 
 Per Cent 
 
 Gross weight 
 
 226.00 
 
 222.00 
 
 
 
 Nitrogen 
 
 1.04 
 
 1. 01 
 
 3-2 
 
 Phosphoric acid .... 
 
 0.61 
 
 0.58 
 
 47 
 
 Potash 
 
 1.20 
 
 0.43 
 
 35-0 
 
 Value per ton .... 
 
 $2.38 
 
 $2.16 
 
 
 197. Losses by Fermentation. — When rapid fermen- 
 tation takes place in manure, appreciable losses of 
 nitrogen may occur. When the manure is well com- 
 pacted and the pile is so constructed as to prevent rapid 
 circulation of air through it, losses are reduced to the 
 minimum. Experiments show that when leaching is 
 prevented, the loss of nitrogen by fermentation of mixed 
 
FARM MANURES 
 
 177 
 
 manure is very small. Under poor conditions losses by- 
 fermentation may exceed 15 per cent. Hen manure, 
 sheep manure, and horse manure are the most ferment- 
 able, particularly when fungous growths and molds are 
 formed. When extreme conditions, as excessive mois- 
 ture, are followed by drought and high temperature, 
 then the greatest losses occur. 
 
 198. Different Kinds of Fermentation. — The large 
 number of organisms present in manure all belong to 
 one of two classes: (i) aerobic, or (2) anaerobic. The 
 aerobic ferments require an abundant supply of air in 
 order to carry on their 
 work. When deprived 
 of oxygen, they become 
 inactive. The anaero- 
 bic ferments require 
 the opposite condition. 
 They become inactive 
 in the presence of oxy- 
 gen and can thrive only ^^^^ ^^- Fermentation of Manure. 
 
 when air is excluded. In the center of a well-constructed 
 manure pile anaerobic fermentation occurs, while on 
 the surface aerobic fermentation is active. The anaer- 
 obic ferments prepare the way for the action of the 
 aerobic. When aerobic fermentation is completed, the 
 organic matter is converted into water, carbon dioxide, 
 ammonia, and allied gases, and these are lost. Conse- 
 quently, anaerobic fermentation is the most desirable. 
 
178 SOILS AND FERTILIZERS 
 
 The bacterial content of the soil is greatly increased 
 by the use of farm manures, and also food is supplied 
 to the organisms already in the soil, many of which take 
 an important part in rendering plant food available. 
 
 199. "Water Necessary for Fermentation. — In order to 
 produce the best results in fermenting manure, water is 
 necessary; for if the manure becomes too dry, abnormal 
 fermentation takes place. Water is always beneficial on 
 manure so long as leaching is prevented, for it encour- 
 ages anaerobic fermentation by excluding the air. An 
 excess of water, such as falls on manure piles from the 
 eaves of buildings, is more than is required for good 
 fermentation. During a dry time it is beneficial to water 
 the compost pile. 
 
 200. Heat produced during Fermentation. — During 
 active fermentation of horse and sheep manure a tem- 
 perature of 175° F. may be reached by the fermenting 
 mass. Ordinarily, however, the temperature of the 
 manure pile ranges from 110° to 130° F. The highest 
 temperature is near the surface, where fermentation is 
 most rapid. The temperature of fermentation may be 
 sufficiently high to cause spontaneous combustion, if the 
 manure is mixed with litter. 
 
 201. Composting Manure may improve its Quality. — 
 
 Composting manure so that leaching and rapid fermen- 
 tation do not take place may improve its quality, mak- 
 
FARM MANURES 
 
 179 
 
 ing it more concentrated. Pound for pound, composted 
 manure is richer in plant food than fresh manure, be- 
 cause, if properly cared for, nearly all of the nitrogen, 
 phosphoric acid, and potash of the original manure are 
 present in smaller bulk. A ton of composted manure is 
 obtained from about 2800 pounds of stable manure. 
 Composting is sometimes resorted to in order to destroy 
 obnoxious weed seeds. 
 
 Nitrogen . . 
 Phosphoric acid 
 Potash . . . 
 
 Fresh 
 
 Composted 
 
 Manure 
 
 Manure 
 
 Per Cent 
 
 Per Cent 
 
 0.50 
 
 0.60 
 
 0.28 
 
 0-39 
 
 0.60 
 
 0.80 
 
 In composting manure it should be the aim to induce 
 anaerobic fermentation by excluding the air and retain- 
 ing the water. This can be accomplished best by using 
 mixed manure and making a compact pile, capable of 
 shedding water. The compost pile should be shaded to 
 secure better conditions for fermentation. If the pile 
 becomes offensive, a little earth on the surface will 
 absorb the odors. 
 
 202. Use of Preservatives. — The use of preservatives, 
 as gypsum and kainit, has been -recommended to prevent 
 fermentation losses. Opinions differ as to the value of 
 this practice. Moist gypsum, when it comes in contact 
 
l8o SOILS AND FERTILIZERS 
 
 with ammonium carbonate, produces ammonium sul- 
 phate, a non-volatile compound, 
 
 (NH4)2C03 + CaSO^ = (NH4)2S04 + CaCOg. 
 
 Gypsum when used should be at the rate of about 
 one half pound per day for each animal.^^ Experiments 
 show that it prevents a loss of 5 per cent of the nitro- 
 gen of horse manure. It has no action on the feet of 
 animals, and so may with safety be sprinkled in the 
 stalls. When it is necessary to use gypsum as a fertilizer, 
 it is advantageous to use it in stables. It is not advis- 
 able to use lime in any other form than the sulphate. 
 Unslaked lime will decompose manure and liberate am- 
 monia. Neither kainit nor gypsum should be used when 
 manure is exposed to the leaching action of rains. Pre- 
 servatives cannot be made to take the place of care in 
 handling manure ; they should be used only when the 
 manure receives the best of care. 
 
 203. Manure produced in Sheds and Box Stalls. — 
 
 Manure produced under cover, as in sheds and box 
 stalls, is of superior quality. Losses by leaching are 
 thus avoided, the manure is compacted by the tramping 
 of the animals, the solid and liquid excrements are more 
 evenly mixed with the absorbents, and the conditions 
 are favorable for anaerobic fermentation. By no other 
 system is there such a large percentage of the fertihty 
 recovered. Manure from well-fed cattle, when collected 
 
FARM MANURES l8l 
 
 and prepared in a covered shed, will have about the 
 following composition : 
 
 Water . . . 
 Nitrogen . . 
 Phosphoric acid 
 Potash . . . 
 
 Per Cent 
 
 70.00 
 
 0.90 
 
 0.60 
 
 0.70 
 
 Manure produced under cover has greater value than 
 when cared for in any other way. Experiments by 
 Kinnard show that such manure produced 4 tons more 
 potatoes per acre than pile manure, while 1 1 bushels 
 more wheat per acre were obtained on land which had 
 the previous year received the covered manure than on 
 land which received the uncovered manure.^^ Experi- 
 ments at the Ohio Station show that stall manure gives 
 a larger crop yield than yard nianure.^^ 
 
 THE USE OF MANURE 
 
 204. Direct Hauling to Fields. — It is always desirable, 
 whenever conditions allow, to draw the manure directly 
 to the field and spread it, rather than to allow it to ac- 
 cumulate about barns or in the barnyard. When taken 
 I directly to the field from the stable no losses by leach- 
 ! ing occur, and the slight losses from fermentation and 
 j volatilization of the ammonia are more than compensated 
 \ for by the benefits derived from the action of the fresh 
 
102 SOILS AND FERTILIZERS 
 
 manure upon the soil. When manure undergoes fer- 
 mentation in the soil, as previously stated, it combines 
 with the mineral matter of the soil and produces humates. 
 The practice of hauling the manure directly to the field 
 and spreading it with a manure spreader is the most eco- 
 nomical way of handling it, as the manure is thus evenly 
 spread, and larger crop returns are secured from the 
 lighter and more frequent applications. 
 
 With scant rainfall composting the manure before 
 spreading is often necessary, but with liberal rainfall it 
 is not essential. On a loam soil, a direct application of 
 stable manure is more advisable than on heavy clay or 
 Hght sandy soil. In the case of sandy soils there is fre- 
 quently an insufficient supply of water properly to fer- 
 ment the manure. Manure on heavy clay land sometimes 
 fails to show any beneficial effect the first year because 
 of the slow rate of decomposition, but the beneficial 
 effects are noticeable the second and third years. 
 
 When conditions will not permit farm manure to be 
 hauled directly to the field and spread, it should be 
 stored in covered manure sheds, so as to prevent leach- 
 ing and injurious fermentation. 
 
 205. Coarse Manure Injurious. — The application of 
 coarse leached manure may cause the soil to be so 
 open and porous as to affect the water supply of the 
 crop, by introducing below the surface soil a layer of 
 straw, and thus breaking the capillary connection with 
 the subsoil. Coarse manure and shallow spring plowing ' 
 
FARM MANURES 
 
 183 
 
 are sometimes injurious, where fine or well-composted 
 manure and fall plowing would be beneficial. Trouble 
 resulting from the use of coarse manure may be due to 
 its being allowed to leach before it is used, so that it 
 does not readily ferment in the soil. 
 
 206. Manuring Pasture Land. — In regions where 
 manure decomposes slowly, it is sometimes advisable to 
 use it upon pasture land as a top dressing. The manure 
 encourages growth of the grass, so that it appropriates 
 plant food otherwise lost ; it also acts as a mulch, pre- 
 venting excessive evaporation. Then when the pasture 
 land is plowed and prepared for a grain crop it contains a 
 better store of both water and available plant food. The 
 manuring of pasture lands is one of the best ways of utiliz- 
 ing manure when trouble arises from slow decomposition. 
 
 207. Small Manure Piles Undesirable. — It is some- 
 times the custom to make a number of small manure 
 piles in fields. This is a poor practice, for it entails 
 additional ex- , ,,,,,,, r- ,v ^/^ ,f.i,.s,u,>un /n^ 
 
 pense later m Mi^IIi^ulj^^ 
 spreading the t^'^-^"' '- - — -"--'- *:r^^ra^- 
 manure, and 
 the small piles 
 are usually 
 constructed in 
 
 such a way Fig. 37. Manured Land. 
 
 that heavy losses occur, so the manure, when finally 
 
1 84 
 
 SOILS AND FERTILIZERS 
 
 ilvift«(S\rir/fi 1^ 
 
 spread, is not uniform in composition. Oats grown on land 
 manured in tliis way presented an uneven appearance. 
 
 , ;| f, „. //.,,! .'//- .^M'/ There were 
 ^^^Ju^-4x^.,j.4-J-^._.U-,..^,.<--^ small patches, 
 
 thrifty and 
 overfed, cor- 
 responding to 
 the places 
 formerly occu- 
 
 FlG. 38. Unmanured Land. • i i 1 
 
 pied by the 
 manure piles, while large areas of half-starved oats 
 miffht be observed. 
 
 208. Rate of Application. — The amount of manure 
 that should be appUed depends upon the nature of the 
 soil and the crop. On loam soils intended for general 
 truck purposes, heavier applications may be made than 
 when grain is raised. For general farm purposes, 8 
 tons per acre are usually sufficient. It is better 
 economy to make frequent and light applications than 
 heavier ones at long intervals. When manure is 
 spread frequently the soil is kept in an even state 
 of fertility, and losses by percolation, denitrification, and 
 ammonification are prevented. Too often the manure 
 is not evenly distributed about the farm ; fields adjacent 
 to stables are heavily manured, while those at a distance 
 receive none. 
 
 For growing garden crops, 20 tons and more per 
 acre are sometimes used. It is better, however, not 
 
FARM MANURES 185 
 
 to use stable manure in excess for trucking, but to 
 supplement it with special fertilizers as the crops may 
 require. Soils which contain a large amount of cal- 
 cium carbonate will not become acid from farm manure, 
 and hence admit of more frequent and heavier applica- 
 tions than soils which are deficient in this compound. 
 The lime aids fermentation and nitrification. Some- 
 times a judicious combination of farm manure and 
 commercial fertilizers can be made that will prove 
 more economical than farm manure alone. 
 
 209. Crops Most Suitable for Manuring. — Soils which 
 contain a low stock of fertiUty admit of manuring for 
 the production of almost any crop. Soils well stocked 
 with plant food, like some of the western prairie soils, 
 which are in need of manure mainly for its physical 
 action, will not allow its direct use on all crops. On 
 a prairie soil of average fertility a heavy application 
 of manure may cause wheat and other grain crops to 
 lodge. When manure cannot be applied directly to 
 a crop, it may be used advantageously on a preced- 
 ing crop and the land thus be brought into good 
 condition for the crop that will not bear direct ma- 
 nuring. Manure never injures corn by causing too 
 rank a growth, and wheat may follow corn which 
 has been manured with but little danger of loss from 
 lodging. 
 
 On some soils stable manure cannot be used for 
 growing sugar beets ; on others it does not seem to exer- 
 
l86 SOILS AND FERTILIZERS 
 
 cise an injurious effect. Tobacco is injured as to quality 
 by manure. Flax, tobacco, sugar beets, and wheat, 
 which should not receive heavy direct applications, all 
 require manuring of the preceding crops. When in 
 doubt as to the crop on which to use the manure, it is 
 always safe to apply it to corn, and then to follow with 
 the crop which would have been injured by its direct 
 application. 
 
 That coarse, leached manure may cause trouble in a 
 dry season, and well-rotted manure may cause grain to 
 lodge, are not valid reasons for manure being wasted as 
 it frequently is in western farming, by being burned, 
 thrown away in streams, used in making roads, or for 
 filling up low places. 
 
 210. Comparative Value of Forage and Manure. — 
 
 The manure from a given amount of grain or fodder 
 always gives better results than if the food itself were 
 used directly as manure. The manure from a ton of 
 bran will give better returns than if the bran itself 
 were used. This is because so little of the fertility 
 is lost during the process of digestion, and the action 
 of the digestive fluids upon the food makes the manure 
 more readily available as a fertilizer than the food 
 which has not passed through any fermentation pro- 
 cess. It is better economy to use products as linseed 
 meal and cottonseed meal for feeding stock, and then 
 take good care of the manure, than to use the mate- 
 rials directly as fertilizer. 
 
FARM MANURES 187 
 
 211. Lasting Effects of Manure. — No other manures 
 make themselves felt for so long a time as farm ma- 
 nures. In ordinary farm practice an application of 
 stable manure will visibly affect the crops for a num- 
 ber of years. At the Rothamsted Experiment Station, 
 records have been kept for over fifty years as to the 
 effects of manures upon soils. In one experiment, 
 farm manure was used for twenty years and then dis- 
 continued for the same period. It was observed that 
 when its use was discontinued there was a gradual 
 decline in crop-producing power, but not so rapid as 
 of plots where no manure had been used. The manure 
 applied during the twenty-year period made itself felt 
 for an ensuing twenty years. 
 
 212. Comparative Value of Manure produced on Two 
 Farms. — The fact that there is a great difference in 
 the composition and value of manures produced on 
 different farms may be observed from the following 
 examples : 
 
 On one farm lo tons of timothy are fed. The 
 liquid manure is not preserved and 25 per cent of the 
 fertility is leached out of the solid excrements, while 5 
 per cent of the nitrogen is lost by volatilization. It is 
 estimated that half of the nitrogen and potash of the 
 food is voided in the urine. On account of the scant 
 amount and poor quality of the food no milk or flesh 
 is produced. 
 
 On another farm 7.5 tons of clover hay and 2.5 tons 
 
l88 SOILS AND FERTILIZERS 
 
 of bran are fed. The liquid excrements are collected 
 and the manure is taken directly to the field and 
 spread. It is estimated that 20 per cent of the nitro- 
 gen and 4 per cent of the phosphoric acid and potash 
 are utilized for the production of flesh and milk. 
 
 The comparative value of the manure from the two 
 farms is as follows : 
 
 Farm No. i 
 
 In 10 Tons Timothy 
 Lbs. 
 
 Nitrogen 250 
 
 Phosphoric acid 90 
 
 Potash 400 
 
 Loss in Urine 
 
 250 -;- 2 = 125 lbs. nitrogen 
 400 -=- 2 = 200 lbs. potash 
 
 Loss by Leaching 
 
 125 X 0.30 = 37.50 lbs. nitrogen 
 90 X 0.25 = 22.50 lbs. phosphoric acid 
 200 X 0.25 = 50 lbs. potash 
 
 Total Loss 
 Lbs. Per Cent 
 
 Nitrogen 162.5 65 
 
 Phosphoric acid . . , . . . . 22.5 25 
 
 Potash 250.0 62 
 
 Present in Final Product 
 Manure from i Ton Timothy 
 Lbs. 
 
 Nitrogen 8.75 
 
 Phosphoric acid 6.75 
 
 Potash 15.00 
 
 Relative money value $1.00 
 
FARM MANURES I 89 
 
 Farm No. 2 
 
 In 10 Tons Mixed Feed 
 Lbs. 
 
 Nitrogen 400 
 
 Phosphoric acid 240 
 
 Potash 300 
 
 Loss, Sold in Milk and Retained in Body 
 Lbs. Per Cent 
 
 Nitrogen, 400 x 0.20 80 20 
 
 Phosphoric acid, estimated ... 10 4 
 
 Potash 12 4 
 
 Present in Final Product 
 
 Manure from i Ton Feed 
 
 Lbs. 
 
 Nitrogen 32.0 
 
 Phosphoric acid 23.0 
 
 Potash 29.0 
 
 Relative money value $3.80 
 
 213. Summary of Ways in which Stable Manure 
 may be Beneficial. — Farm manures act upon soils 
 chemically, physically, and bacteriologically. 
 (a) Chemically : 
 
 1. By adding new stores of plant food to the soil. 
 
 2. By combining with the soil, forming humates, and 
 rendering the inert mineral plant food more available. 
 
 3. By raising the temperature of the soil, as the re- 
 sult of oxidation. 
 
 (d) Physically : 
 
 1. By making the soil darker colored. 
 
 2. By enabling soils to retain more water and to give 
 it up gradually to growing crops. 
 
190 SOILS AND FERTILIZERS 
 
 3, By improving the tilth of sandy and clay soils. 
 
 4. By preventing the denuding effects of heavy wind 
 storms. 
 
 (c) Bacteriologically : 
 
 1. By increasing the number of soil organisms. 
 
 2. By promoting fermentation changes. 
 
 3. By supplying food to the organisms which assist 
 in rendering plant food available. 
 
CHAPTER VI 
 
 FIXATION 
 
 214. Fixation, a Chemical Change. — When a fer- 
 tilizer is applied to a soil, chemical reaction takes 
 place between the soil and the fertilizer. There is 
 a general tendency for the soluble matter of fertilizers 
 to undergo chemical change and become insoluble. 
 This process is known as fixation. If a solution of 
 potassium chloride be percolated through a column of 
 clay, the filtrate will contain scarcely a trace of potas- 
 sium chloride, but instead calcium and other chlorides. 
 The element potassium of the potassium chloride has 
 been replaced by the element calcium present in the 
 soil, and as a result of this exchange of base elements 
 an insoluble compound of potash is formed. Indepen- 
 dent of chemical action, a small amount of soluble salts 
 are absorbed physically by soils and retained by molec- 
 ular force. Absorption is a physical property of soils, 
 while fixation is due to a chemical change. 
 
 215. Fixation due to Zeolites. — It has been shown by 
 experiments, particularly those of Way and Voechler,^^ 
 that fixation is due mainly to zeolitic silicates. Sandy 
 soils containing but little clay have only feeble power 
 of fixation. Clay soils when digested with hydrochloric 
 
 191 
 
192 SOILS AND FERTILIZERS 
 
 acid to remove the zeolitic silicates lose their power of 
 fixation. The fixation of potassium chloride and the 
 liberation of calcium chloride may be illustrated by the 
 following reaction : 
 
 Zeolite Zeolite 
 
 AI2O3 
 K.,0 
 
 ^■(Si02)^-H.20 + 2KC1 = ^ ^ 
 etc. 
 
 ;r(Si02)x-H20 + CaCla. 
 
 216. Humus may cause Fixation. — Also other com- 
 pounds of the soil, as humus and calcium carbonate, 
 take an important part in fixation. In the case of 
 humus, a union occurs between the minerals in the 
 fertihzer and the organic acids formed from the decay 
 of the humus in the soil, resulting in the production of 
 humates. 
 
 217. Variations in Fixative Power of Soils. — All soils 
 do not possess the power of fixation to the same extent. 
 Heavy clays have the greatest fixative power, while 
 sandy soils have the least. As a general rule, soils of 
 high fertility show good fixative power. Hence it is 
 that a fertilizer, after being applied to a soil, may be 
 entirely changed in composition, so that the plant feeds 
 on the chemical products formed, rather than on the 
 original fertilizer. . 
 
 218. Fixation of Phosphates. — The phosphates of 
 fertilizers readily undergo fixation by combination with 
 
FIXATION 193 
 
 the iron and aluminum compounds of soils, forming in- 
 soluble phosphates. Experiments show that in a loam 
 soil from 2000 to 8000 pounds per acre of phosphoric 
 acid may undergo fixation. Drainage waters contain 
 only traces of phosphates. At the Rothamsted Experi- 
 ment Station the plots receiving an annual dressing of 
 phosphates for fifty years contained 83 per cent of the 
 surplus fertilizer, half of which was in available forms 
 soluble in one per cent citric acid.^^ 
 
 219. Fixation of Potash. — The potash compounds of 
 fertilizers readily undergo fixation, the sodium and cal- 
 cium of the soil being replaced by the potassium of the 
 fertihzer. Drainage waters contain larger amounts of 
 sodium than of potassium compounds, due to greater in- 
 solubility of the potash of the soil. Fixation of potash 
 occurs mainly in the surface soil, where it is held in 
 forms insoluble in water, a portion being soluble in 
 dilute acids. 
 
 220. Nitrates cannot undergo Fixation. — Nitrogen in 
 the form of nitrates or nitrites cannot undergo fixation. 
 This is because all of the ordinary forms of nitrates are 
 soluble. If potassium nitrate be added to a soil, calcium 
 or sodium nitrate will be obtained as the soluble com- 
 pound. The potassium undergoes fixation, but the ni- 
 trate radical does not. Chlorides also are incapable of 
 undergoing fixation, because all of the chlorides found 
 in soils are soluble. 
 
194 SOILS AND FERTILIZERS 
 
 221. Fixation of Ammonia. — Ammonium compounds 
 readily undergo fixation, particularly in the presence of 
 clay. (See experiment No. 17.) The ammonium radi- 
 cal, NH4,like potassium, is capable of replacing soil 
 bases. After undergoing fixation, the ammonium com- 
 pounds readily yield to nitrification (see Section 156), 
 hence they serve as a temporary but important form of 
 insoluble nitrogen. The general tendency of the nitro- 
 gen compounds of the soil is to pass from insoluble to 
 soluble forms through processes of decay, and to resist 
 fixation changes. 
 
 222. Fixation may make Plant Food Less Avail- 
 able. — If a very heavy dressing of potash or phosphate 
 fertilizer be applied to a heavy clay soil, what is not 
 utilized the first few years may undergo fixation to such 
 an extent that part becomes unavailable as plant food. 
 It is not well to apply unnecessarily heavy dressings of 
 fertilizers at long intervals because of fixation. It is 
 always best to make light and frequent applications. 
 
 223. Fixation, a Desirable Property for Soils. — If it 
 were not for the process of fixation, soils in regions of 
 heavy rains would soon become sterile. When the 
 plant food has become insoluble, it is retained in the 
 soil. That which undergoes fixation is, as a rule, in an 
 available condition or may readily become so by cultiva- 
 tion unless the soil be one of unusual composition. The 
 process of fixation regulates the supply of plant food in 
 
FIXATION 
 
 195 
 
 the soil. Many fertilizers, if they did not undergo this 
 process, would be injurious to crops, for there would be 
 an abnormal amount of soluble alkahne or acid com- 
 pounds which would be destructive. When the process 
 
 Fig. 39. Plants grown in Normal Soil. 
 
 of fixation takes place, it removes, to a great extent, 
 injurious water-soluble salts, particularly when the reac- 
 tion is one of union rather than replacement. Then 
 the plant is free to render soluble its own food in quan- 
 tities and at times desired. 
 j Farm manures and commercial fertilizers alike un- 
 ; dergo the process of fixation and, in studying ferti- 
 I lizers, their action upon the soil and the products of 
 I fixation are matters of prime importance. 
 
196 
 
 SOILS AND FERTILIZERS 
 
 224. Soil Solution. — Soil water obtained by leaching 
 soils is an exceedingly dilute solution of various mineral 
 salts and organic compounds. Through rock disinte- 
 gration, mineral matter is rendered soluble, but the pro- 
 cess of fixation prevents accumulation in the soil solution 
 
 Fig. 40. 
 
 Plants grown in Sand and watered with Leachings (Soil Solu- 
 tion) from Soil as used in Fig. 39. 
 
 of compounds of such elements as potassium and phos- 
 phorus. As a result of disintegration and fixation, 
 numerous chemical changes take place in the soil, and 
 the soil solution is an important factor in bringing about 
 these changes. Many of the phenomena which have 
 been studied in connection with solutions in physical 
 chemistry take place in the soil. Diffusion, absorption, 
 osmotic pressure, and ionization,^^ — disassociation of the 
 molecule in solution, — all occur in soils and are due 
 
FIXATION 197 
 
 largely to the physical and chemical action of the soil 
 solution. The soil solution from different soils varies 
 with the composition and degree of disintegration of 
 the soil particles, and in the same soil at different times 
 there are variations in its composition. The soil solution 
 is more important as an agent for bringing about chem- 
 ical and physical changes in the soil than as a store- 
 house of plant food. It is not possible to exhaust a soil 
 of all of its water-soluble salts by one or more leachings. 
 There appears to be a variable but fairly continuous 
 solubility of soil constituents. King has shown that 
 soils of high productiveness contain a larger amount of 
 soluble salts than soils of low fertility.^" 
 
CHAPTER VII 
 
 PHOSPHATE FERTILIZERS 
 
 Fig. 41. Oat Plant grown without 
 Phosphates. 
 
 225. Importance of Phos- 
 phorus as Plant Food. — 
 
 Phosphorus in the form of 
 phosphates is one of the 
 essential elements of plant 
 food. None of the higher 
 orders of plants can complete 
 their growth unless supplied 
 with this element. The il- 
 lustration (Fig. 41) shows an 
 oat plant which received no 
 phosphorus compounds, but 
 was supplied with all the 
 other elements of plant food. 
 As soon as the phosphoric 
 acid stored up in the seed 
 had been utiHzed, the plant 
 ceased to grow, and after a 
 few weeks, died of phosphate 
 starvation, having made the 
 total growth shown in the 
 illustration. All crops de- 
 mand their phosphorus com- 
 pounds at an early stage of 
 development. Wheat takes 
 198 
 
PHOSPHATE FERTILIZERS 1 99 
 
 up 80 per cent of its phosphoric acid in the first half of the 
 growingperiod,^'^ while clover has assimilated all it requires 
 by the time the plant reaches full bloom.^^ Phosphorus 
 compounds accumulate, to a great extent, in the seeds 
 of grains, and hence, when grain farming is extensively 
 followed, are sold from the farm. All crops are very 
 sensitive to the absence of phosphoric acid ; an imper- 
 fect supply results in the production of light-weight 
 grain. The nitrogen and phosphorus are to a great 
 extent stored up in the same parts of the plant, par- 
 ticularly in the seed, which is richer in both of these 
 elements than is any other part. Nitrogen is the chief 
 element of protein, while phosphorus is also necessary 
 for the formation of some of the phosphorus and ni- 
 trogen compounds, as the nucleo-albumins and lecithin. 
 Phosphorus aids in the production of the protein com- 
 pounds. In speaking of the phosphorus compounds in 
 plants and in fertilizers, as well as in soils, the term 
 'phosphoric anhydride' or 'phosphorus pentoxide,' P2O5, 
 commonly called phosphoric acid, is used. This is be- 
 cause phosphorus is an acid-forming element and, as 
 already explained, the anhydride of the element is al- 
 ways considered instead of the element itself. 
 
 226. Amount of Phosphoric Acid removed in Crops. — 
 
 Grain crops remove about 20 pounds per acre of phos- 
 phoric acid; the amount removed by other farm crops 
 ranges from 18 to 28 pounds, as will be observed from 
 the following table : 
 
200 
 
 SOILS AND FERTILIZERS 
 
 Wheat, 20 bu. . . 
 
 Straw, 2000 lbs. . . 
 
 Total . . . 
 
 Barley, 40 bu. . . 
 
 Straw, 3000 lbs. . . 
 
 Total . . . 
 
 Oats, 50 bu. . . . 
 
 Straw, 3000 lbs. . . 
 
 Total . . . 
 
 Corn, 65 bu. . . . 
 
 Stalks, 4000 lbs. . . 
 
 Total . . . 
 
 Peas, 3500 lbs. . . 
 Red clover, 4000 lbs. 
 Potatoes, 150 bu. 
 
 Flax, 15 bu. . . . 
 
 Straw, 1800 lbs. . . 
 
 Total . . . 
 
 Phosphoric Acid 
 
 P2O5 
 
 Per Acre 
 
 Lbs. 
 
 12.5 
 
 7-5 
 20.0 
 
 20 
 
 12 
 
 6 
 
 Ts 
 18 
 
 4 
 22 
 
 25 
 28 
 
 20 
 
 15 
 3 
 
 227. Amount and Source of Phosphoric Acid in Soils. 
 
 — To meet the demand of growing crops for about 25 
 pounds of phosphoric acid per acre, there are present in 
 soils from 0.03 to 0.25 per cent. This is equivalent to 
 from 1000 pounds and less to 9000 pounds per acre, of 
 which, however, only a fraction is available as plant food at 
 
PHOSPHATE FERTILIZERS 201 
 
 any one time. The availability of the phosphoric acid has 
 a great deal to do in determining crop-producing power. 
 Many soils contain a large amount of total phosphoric 
 acid which has become unavailable, because of poor cul- 
 tivation and absence of stable manure and lime to com- 
 bine with the phosphates and render them available. 
 
 The phosphates in soils are derived mainly from the 
 disintegration of phosphate rock and from the remains 
 of animal life. The phosphate deposits found in various 
 localities are supposed to have had their origin either 
 in the remains of marine animals or sea water highly 
 charged with soluble phosphates. These deposits have 
 been subjected to various geological and climatic changes 
 which have resulted in the formation of soft phosphate, 
 pebble phosphate, and rock phosphate.^^ 
 
 228. Commercial Forms of Phosphoric Acid. — The 
 
 sources of phosphate fertilizers are : (i) phosphate rock, 
 (2) bones and bone preparations, (3) phosphate slag, and 
 (4) guano. With the exception of phosphate slag and 
 guano, the prevailing form of phosphorus is tricalcium 
 phosphate. Before being used for commercial purposes 
 the tricalcium phosphate, which is insoluble and unavail- 
 able, is treated with sulphuric acid, which produces mono- 
 calcium phosphate, a soluble and available form. 
 
 Ca3(P04)2 + 2 H2SO4 -h 5 H2O = CaH4(P04)2 + H^O + 
 2 CaS04, 2 H2O. 
 
 In making phosphate fertilizers from bones or phos- 
 
202 SOILS AND FERTILIZERS 
 
 phate rock, an excess of the rock is used so there will be 
 no free acid in the fertilizer to be injurious to vegetation. 
 As stated above, the usual form in which calcium phos- 
 phate is found in nature is tricalcium phosphate, 
 Ca3(P04)2, and unless associated with organic matter 
 or salts which render it soluble, it is of but little value as 
 plant food. When tricalcium phosphate is treated with 
 sulphuric acid, monocalcium phosphate, Ca.}ri^(F0^)2, is 
 formed, which is soluble in water and directly available 
 as plant food. When tricalcium and monocalcium phos- 
 phate are brought together in a moist condition, dical- 
 cium phosphate is produced. 
 
 CagCPO^)., + CaH^CPO^).^ = 2 Ca2H2(P04)2. 
 
 Another form of phosphate of lime, met with in basic 
 phosphate slag, is tetracalcium phosphate, (CaO)4P20g. 
 
 229. Reverted Phosphoric Acid. — When mono- and 
 tricalcium phosphate react, the product is known as re- 
 verted phosphoric acid, which is insoluble in water, but 
 is not in such form as to be unavailable as plant food ; it 
 is generally considered available. Reverted phosphoric 
 acid may also be formed by the action, upon mono- 
 calcium phosphate, of iron and aluminum compounds 
 present as impurities in the phosphate rock. As it is 
 soluble in a dilute solution of ammonium citrate, it is 
 sometimes spoken of as citrate-soluble phosphoric acid, 
 and is not all equally valuable as plant food because of 
 the different phosphate compounds that may be dissolved 
 
PHOSPHATE FERTILIZERS 203 
 
 by this solvent. Citrate-soluble phosphoric acid may be 
 present in an old fertilizer in two forms, — dicalcium 
 phosphate and hydrated phosphates of iron and alumi- 
 num. 
 
 230. Available Phosphoric Acid. — As applied to fer- 
 tilizers, the term 'available phosphoric acid' includes the 
 water-soluble and citrate-soluble phosphoric acid. These 
 solvents do not, under all conditions, make a sharp dis- 
 tinction as to the available and unavailable phosphoric 
 acid when it comes to plant growth. Some forms of 
 bone which are insoluble in an ammonium citrate solu- 
 tion are available as plant food, while some forms of 
 aluminum phosphate which are soluble are of but little 
 value. The fineness of division of the fertilizer particles 
 also greatly influences the availability of the phosphoric 
 acid. The terms 'available' and ' unavailable phosphoric 
 acid,' as applied to commercial fertilizers, refer to the 
 solubility of the phosphates, and, as a rule, the value of 
 the phosphates as plant food is in accord with their sol- 
 ubility — the more insoluble the less valuable. 
 
 231. Phosphate Rock. — Phosphate rock is found in 
 many parts of the United States, particularly in South 
 Carolina, North Carolina, Florida, Virginia, and Tennes- 
 see. The deposits occur in stratified veins, as well 
 as in beds and pockets. There are different types 
 of phosphates, as hard rock, soft rock, land pebble, 
 and river pebble. The pebble phosphates are found 
 
204 SOILS AND FERTILIZERS 
 
 either on land or collected in cavities in water courses, 
 and are generally spherical masses of variable size. 
 Soft rock phosphate is easily crushed, while the hard 
 rock requires pulverizing with rock crushers. Phosphate 
 rock usually contains from 40 to 70 per cent of calcium 
 phosphate, the equivalent of from 17 to 30 per cent 
 phosphoric acid. The remaining 30 to 60 per cent is 
 fine sand, limestone, alumina, and iron compounds, with 
 other impurities, which often render a phosphate un- 
 suitable for manufacture into high-grade fertilizer. 
 
 232. Superphosphate. — Pulverized rock phosphate, 
 known as phosphate flour, is treated with commercial 
 sulphuric acid to obtain soluble monocalcium phosphate. 
 The amount of sulphuric acid used is determined by the 
 composition of the rock. Impurities as calcium carbon- 
 ate and calcium fluoride react with sulphuric acid and 
 cause a loss of the acid. Ordinarily, a ton of high-grade 
 phosphate rock requires a ton of sulphuric acid. The 
 mixing is done in lead-lined tanks. A weighed amount 
 of phosphate flour is placed in the tank and the sulphuric 
 acid added, through lead pipes, from the acid tower. The 
 mixing of the acid and phosphate is done with a mechani- 
 cal mixer, driven by machinery. From the mixing tank 
 the material is passed into other large tanks, where two 
 or three days are allowed for the completion of the 
 reaction. The mass is placed in piles to solidify and is 
 then ground and sold as superphosphate. In the manu- 
 facture of superphosphate, gypsum (CaS04.2H20) is 
 
PHOSPHATE FERTILIZERS 20$ 
 
 always produced. A ton of superphosphate prepared 
 from high-grade rock in the way outlined will contain 
 about 40 per cent of Hme phosphate, equivalent to i8 
 per cent phosphoric acid. If a poorer quality of rock 
 is used, there is a proportionally smaller amount of phos- 
 phoric acid. A more concentrated superphosphate is 
 known as double superphosphate and is obtained by pro- 
 ducing phosphoric acid from the phosphate rock, and 
 then allowing the phosphoric acid to act upon fresh por- 
 tions of the rock, the reactions being as follows : ^* 
 
 Ca3(P04)2 -h 3 H.2SO4 = 3 CaSO^ + 2 HgCPO^). 
 Ca3(POj2 + 4 H3PO4 + 3 H2O = 3[CaH4(P04)2, H^O]. 
 
 The phosphoric acid is separated from the gypsum 
 before acting upon the phosphate flour. In this way, 
 superphosphate containing from 35 to 45 per cent of 
 phosphoric acid is produced. When fertilizers are to be 
 transported long distances, this concentrated product is 
 preferable. The terms ' acid ' and ' superphosphate ' 
 have been generally used to designate the first product 
 resulting from the action of sulphuric acid upon phos- 
 phate rock or bones, and the term ' double superphos- 
 phate ' to mean the concentrated product formed by the 
 action of phosphoric acid. 
 
 233. Commercial Value of Phosphoric Acid. — The com- 
 mercial value of phosphoric acid in fertilizers is deter- 
 mined by the value of the crude phosphate rock, cost 
 of grinding and treating with sulphuric acid, and cost of 
 
206 SOILS AND FERTILIZERS 
 
 transportation. The price of phosphoric acid in super- 
 phosphates usually ranges from 5 to 6 cents per pound. 
 The field value, that is the increased yields obtained 
 from the use of superphosphates, may .or may not be in 
 accord with the commercial value because so many con- 
 ditions influence crop growth. The phosphoric acid ob- 
 tained from feed stuffs is usually considered worth about 
 a cent a pound less than that from superphosphates. 
 Water-soluble phosphoric acid is generally rated a half 
 cent per pound higher than citrate-soluble phosphoric 
 acid. 
 
 234. Phosphate Slag. — In the refining of iron ores by 
 the Bessemer process, the phosphorus in the iron is re- 
 moved as a basic slag. The lime, which is used as a 
 flux, melts and combines with the phosphorus of the 
 ore, forming phosphate of lime. The slag has a variable 
 composition. The process by which the phosphorus of 
 pig iron is removed and converted into basic phosphate 
 slag is known as the Thomas process, and the product 
 is sometimes called Thomas' slag. At the present time 
 but little basic slag is produced in this country that is 
 suitable for fertilizer purposes. In Germany and some 
 other European countries large amounts are produced 
 and used. Phosphate slag is ground to a fine powder 
 and is applied directly to the land, without undergoing 
 the sulphuric acid treatment. The phosphoric acid is 
 present mainly in the form of tetracalcium phosphate 
 (CaO)^?^©^. 
 
PHOSPHATE FERTILIZERS 20/ 
 
 235. Guano is the Spanish for dung and is a concen- 
 trated form of nitrogenous and phosphate manure, of in- 
 terest mainly on account of its historic significance. It 
 is a mixture of sea-fowl droppings, with dead animals and 
 debris, which have accumulated along the seacoast in 
 sheltered regions and undergone fermentation. The 
 introduction of guano into Europe marked an important 
 period in agriculture, inasmuch as its use demonstrated 
 the action and value of concentrated fertilizers. All of 
 the best beds of guano have been exhausted and only a 
 little of the poorer grades is now found on the market. 
 The best qualities of guano contained from 12 to 15 per 
 cent of phosphoric acid, 10 to 12 per cent of nitrogen, 
 and from 5 to 7 per cent of alkaline salts. 
 
 BONE FERTILIZERS 
 
 236. Raw Bones contain, in addition to phosphate of 
 lime, Ca3(P04)2, organic matter which makes them slow 
 in decomposing and slow in their action as a fertilizer. 
 Before being used as a fertiUzer they should be fer- 
 mented in a compost heap with wood ashes in the follow- 
 ing way, a protected place being selected so that no losses 
 from drainage will occur. A layer of well-compacted 
 manure is covered with wood ashes, the bones are then 
 added and well covered with ashes and manure. From 
 three to six months should be allowed for the bones to 
 ferment. The large, coarse pieces may then be crushed 
 and are ready for use. The presence of fatty material 
 
208 SOILS AND FERTILIZERS 
 
 in a fertilizer retards its action because fat is so slow- 
 in decomposing. Bones from which the organic matter 
 has been removed are more active as a fertiHzer than raw 
 bones. There is from i8 to 25 per cent of phosphoric 
 acid and from 2 to 4 per cent of nitrogen in bones. 
 The amount and value of the citrate-soluble phosphoric 
 acid are extremely variable. 
 
 237. Bone Ash is the product obtained when bones 
 are burned. It is not extensively used as a fertilizer 
 because of the greater commercial value of bone black. 
 Bone ash contains about 36 per cent of phosphoric acid, 
 and is more concentrated than raw bones. 
 
 238. Steamed Bone. — Raw bones are subjected to 
 superheated steam to remove the fat and ossein which 
 are used for making soap and glue. They are then pul- 
 verized and sold as fertiHzer under the name of bone meal, 
 which contains from 1.5 to 2.5 per cent of nitrogen and 
 from 22 to 29 per cent of phosphoric acid. Steamed 
 bone makes a more active fertilizer than raw bone. Oc- 
 casionally well-prepared bone meal is used for feeding 
 pigs and fattening stock in the same way that flesh meal 
 is used. The fineness to which the bone meal is ground 
 greatly influences its agricultural value. 
 
 239. Dissolved Bone. — When bones are treated with 
 sulphuric acid, as in the manufacture of superphosphates, 
 the product is called dissolved bone. The tricalcium 
 
PHOSPHATE FERTILIZERS 2O9 
 
 phosphate undergoes a change to more available forms, 
 as described, and the nitrogen is rendered more available. 
 Dissolved bone contains from 2 to 3 per cent of nitrogen 
 and from 15 to 17 per cent of phosphoric acid. 
 
 240. Bone Black. — When bones are distilled, bone 
 black is obtained. It is extensively employed for refin- 
 ing sugar, and after it has been used and lost its power 
 of decolorizing solutions it is occasionally sold for fertili- 
 zer. It is a concentrated phosphate fertilizer, containing 
 about 30 per cent phosphoric acid. 
 
 241. Use of Phosphate Fertilizers. — The amount of 
 a phosphoric acid fertilizer that it is advisable to apply 
 to crops varies with the nature of the soil and the kind 
 of crop to be produced. On a poor soil 400 pounds of 
 acid phosphate per acre is an average application. It is 
 usually appHed as a top dressing just before seeding, and 
 may be placed near but not in contact with the seed. It 
 is not advisable to make heavy applications of superphos- 
 phates at long intervals, because fixation may take place 
 to such an extent that crops are unable to utilize the 
 fertilizer. Lighter and more frequent applications, as 
 100 to 200 pounds per acre, are preferable. Phosphates 
 should not be mixed with lime carbonate before spread- 
 ing, but be appHed directly to the land.^^ Phosphates 
 may be used in connection with farm manures. Many 
 soils which contain Hberal amounts of phosphoric acid 
 are improved by a light dressing of phosphates, 75 pounds 
 
210 
 
 SOILS AND FERTILIZERS 
 
 per acre. Such soils, however, should be more thor- 
 oughly cultivated, and manured with farm manures, to 
 make the phosphates available. There is frequently 
 an apparent lack of phosphoric acid when in reality the 
 trouble is due to other causes, as a deficiency of lime or 
 organic matter to render the phosphates available. Be- 
 fore using phosphate fertilizers, careful field tests should 
 be made to determine the needs of the soil. 
 
 242. How to keep the Phosphoric Acid Available. — 
 
 Phosphoric acid associated with organic matter in a 
 moderately alkaline soil is more available than that in acid 
 soils. Soft phosphate rock may be mixed with manure or 
 material like cottonseed meal and made slowly available 
 for crops, but where land is high in price such a pro- 
 cedure is not economical. Soils which contain a good 
 stock of phosphoric acid, when kept well manured and 
 occasionally limed if necessary, have a liberal supply 
 of available phosphoric acid. The following is an 
 example of two soils from adjoining farms, which 
 have been cropped and manured differently.^^ 
 
 
 
 Soil well 
 
 No Manure and 
 
 
 
 MANURED AND 
 
 CONTINUOUS Wheat 
 
 
 
 Ckops Rotated 
 
 Raising 
 
 
 
 Per Cent 
 
 Per Cent 
 
 Total phosphoric acid . . 
 
 
 0.20 
 
 0.20 
 
 Humus 
 
 
 4.25 
 
 1.62 
 
 Phosphoric acid dissolved 
 
 with 
 
 
 humus 
 
 
 0.06 
 
 0.02 
 
PHOSPHATE FERTILIZERS 211 
 
 When the soil contains a liberal supply of total phos- 
 phoric acid, it is more economical to change the phos- 
 phoric acid of the soil to available forms by the use of 
 farm manures, lime, rotation of crops, and thorough 
 cultivation, than it is to purchase superphosphates in com- 
 mercial forms. 
 
CHAPTER VIII 
 
 POTASH FERTILIZERS 
 
 Fig. 42. 
 
 Oat Plant grown without Potash, 
 
 212 
 
 243. Potassium an Es- 
 sential Element of Plant 
 Food. — Potassium is one 
 of the three elements 
 most essential as plant 
 food. In its absence 
 plants are unable to de- 
 velop. Oats seeded in 
 a sterile soil from which 
 potassium salts only were 
 withheld made the total 
 growth shown in the illus- 
 tration ( Fig. 42). In dis- 
 cussing the content of 
 potassium compounds in 
 plants, soils, and food 
 stuffs, the term 'potash' 
 (potassium oxide, K3O) 
 is used. When present 
 in the soil in liberal 
 amounts and associated 
 with other essential ele- 
 ments, potash produces 
 
POTASH FERTILIZERS 
 
 213 
 
 vigorous plants. Like phosphoric acid and nitrogen, it 
 is utilized by crops in the early stages of growth. It does 
 not accumulate in seeds to the same extent as phosphoric 
 acid and nitrogen, but is present mainly in stems and 
 leaves ; consequently when straw crops are utilized in pro- 
 ducing manure, the potash is not lost, or as in the case of 
 nitrogen, sold from the farm. But with ordinary grain 
 farming excessive losses of potash do occur, particularly 
 when the straw is burned and the ashes are wasted. 
 
 244. Amount of Potash removed in Crops. — In grain 
 crops from 35 to 60 pounds of potash per acre are removed 
 from the soil. For grass crops more potash is required 
 than for grains, while roots and tubers require more than 
 grass. The approximate amount of potash removed in 
 various crops is given in the following table : 
 
 Potash per Acre 
 K,0 
 Lbs. 
 
 Wheat, 20 bu. 
 Straw, 2000 lbs. 
 
 Total 
 Barley. 40 bu. 
 Straw, 3000 lbs. 
 
 Total 
 Oats, 50 bu. 
 Straw, 3000 lbs. 
 
 Total 
 
 35 
 
 8 
 
 30 
 
 "38 
 10 
 
 35^ 
 45 
 
214 
 
 SOILS AND FERTILIZERS 
 
 Corn, 65 bu. . . . 
 Stalks, 3000 lbs. . 
 
 Total . . 
 Peas, 30 bu. 
 
 Straw, 3500 lbs. . . 
 
 Total . . . 
 
 Flax, 15 bu. . . . 
 
 Straw, 1800 lbs. . . 
 
 Total . . 
 
 Mangels, 10 tons . . 
 
 Meadow liay, i ton . 
 Clover hay, 2 tons 
 Potatoes, 1 50 bushels 
 
 Potash per Acre 
 Lbs. 
 
 15 
 
 4^ 
 
 60 
 22 
 38 
 60 
 8 
 
 27 
 
 150 
 
 45 
 66 
 
 75 
 
 245. Amount of Potash in Soils. — Ordinarily there 
 is in soils from o. i to 0.5 per cent of potash, equivalent to 
 from 3500 to 18,000 pounds per acre to the depth of 
 one foot. Many soils with apparently a good stock of 
 total potash give excellent results when a light dressing 
 of potash salts is applied. The amount of available 
 potash in a soil is more difficult to estimate than the 
 available phosphoric acid. There is much difference in 
 crops as to their power of obtaining potash ; some re- 
 quire greater help in procuring it than others. A lack 
 
POTASH FERTILIZERS 21$ 
 
 of available potash is sometimes indirectly due to a 
 deficiency of lime or other alkaline matter in the soil, 
 which prevents the necessary chemical changes taking 
 place in order that the potash may be liberated as plant 
 food. 
 
 246. Sources of Potash in Soils. — The main source 
 of the soil's potash is feldspar, which, after disintegra- 
 tion, is broken up into kaolin and potash compounds. 
 Mica and granite also, in some localities, contribute lib- 
 eral amounts, and the zeolitic silicates are a valuable 
 source of potash. There is but little water-soluble pot- 
 ash except in alkaline soil. By the action of many fer- 
 tilizers the potash compounds undergo changes in com- 
 position. For example, the gypsum which is always 
 present in acid phosphates liberates some potash. The 
 potash compounds of the soil are in various degrees of 
 complexity from forms soluble in dilute acids to insoluble 
 minerals as feldspar. 
 
 247. Commercial Forms of Potash. — Prior to the in- 
 troduction of the Stassf urt salts, wood ashes were the main 
 source of potash. Since the discovery and development 
 of the Stassfurt mines, the natural products, as kainit, 
 and muriate and sulphate of potash, have been exten- 
 sively used for fertilizing purposes. A small amount of 
 potash is obtained also from waste products, as tobacco 
 stems, cottonseed hulls, and the refuse from beet-sugar 
 factories. 
 
2l6 SOILS AND FERTILIZERS 
 
 STASSFURT SALTS 
 
 248. Occurrence.^* — The Stassfurt mines were first 
 worked with the view of procuring rock salt. The va- 
 rious compounds of potash, soda, and magnesia, asso- 
 ciated with the layers of rock salt, were regarded as 
 troublesome impurities, and attempts were made by 
 sinking new shafts to avoid them, but with the resu!t 
 of finding them in greater abundance. About 1864 
 their value as potash fertilizer was established. It is 
 supposed that at one time the region about the mines 
 was submerged and filled with sea water. The tropi- 
 cal climate of that geological period caused rapid evapo- 
 ration, which resulted in forming mineral deposits, the 
 less soluble material as lime sulphate being first depos- 
 ited, then a layer of rock salt, and finally layers of pot- 
 ash and magnesium salts in the order of their solubility. 
 
 249. Kainit is a niineral composed of potassium 
 sulphate, magnesium sulphate, magnesium chloride, and 
 water of crystallization. As it comes from the mine 
 it is mixed with gypsum, salt, potassium chloride, and 
 other bodies. Kainit contains about 12 per cent potash 
 and is one of the most important of the Stassfurt salts. 
 It is extensively used as a potash fertilizer, and is also 
 mixed with other materials and sold as a complete fer- 
 tilizer. The magnesium chloride causes it to absorb 
 water, and the presence of other compounds results 
 in the formation of hard lumps, whenever kainit is 
 
POTASH FERTILIZERS 217 
 
 kept for a long time. Kainit is soluble in water 
 and can be used as a top dressing at the rate of 75 
 to 200 pounds or more per acre. 
 
 250. Muriate of Potash. — This is extensively used as 
 a fertilizer and is valuable for general garden and farm 
 crops. It is a manufactured product, — potassium chlo- 
 ride, — and ranges in purity from 60 to 95 per cent, 
 equivalent to from 35 to 60 per cent of potash, the 
 chief impurity being sodium chloride. The grade most 
 commonly found on the market contains about 50 
 per cent of actual potash, equivalent to 80 per cent 
 of muriate. Potassium chloride is readily soluble and 
 is a quick-acting fertilizer. When used in large 
 amounts, muriate of potash and other chlorides may un- 
 favorably affect the quality of some crops, as potatoes, 
 sugar beets, and tobacco. Ordinarily, muriate of pot- 
 ash is one of the cheapest and most active forms of 
 potash, and can be used as a top dressing at the rate 
 of 200 pounds or more per acre when preparing 
 soils for crops. It is valuable for grass and grain 
 crops, and has given good results on peaty lands.^^ 
 
 251. Sulphate of Potash. — High-grade sulphate of 
 potash is prepared from some of the crude Stassfurt 
 salts and may contain as high as 97 per cent K2SO4, 
 equivalent to 50 per cent of potassium oxide (KgO). It 
 is one of the most concentrated forms of potash fer- 
 tilizer and is particularly valuable because it can be 
 
2l8 
 
 SOILS AND FERTILIZERS 
 
 applied safely to crops, as tobacco and potatoes, which 
 would be injured in quality if muriate of potash were 
 used, or if much chlorine were present. Low-grade 
 sulphate of potash is 90 per cent pure. 
 
 252. Miscellaneous Potash Salts. — Carnallit, 9 per 
 cent K^O, — composed of KCl,MgCl2,6 H2O. Polyha- 
 lit, 15 per cent K2O, — composed of K3S04,MgS04. 
 (CaS04)2,H20. Krugit, 10 per cent K2O, — composed 
 of K2Sd'4,MgS04,(CaS04)4,H30. Sylvinit, 16 to 20 per 
 cent KgO, — composed of KCl,NaCl and impurities. 
 Kieserit, 7 per cent K2O, — composed of MgS04 and 
 carnallit. 
 
 253. Wood Ashes. — For ordinary agricultural pur- 
 poses, wood ashes are an important source of potash, 
 although they are exceedingly variable in composition. 
 When leached the soluble salts are extracted and there 
 is left only about i per cent of potash. In unleached 
 ashes the amount of potash ranges from 2 to 10 per 
 cent. Soft wood ashes contain much less potash than 
 hard wood ashes. Goessmann gives the following as 
 the average of 97 samples of ashes : ^^ 
 
 Average 
 
 Composition 
 
 Per Cent 
 
 Range 
 Per Cent 
 
 Potash . . . 
 Phosphoric acid 
 Lime 
 
 5-5 
 1.9 
 
 34-3 
 
 2,5 to 10.2 
 0.3 to 4.0 
 180 to 50.9 
 
potash fertilizers 
 In 10,000 Pounds of Wood 
 
 219 
 
 Phosphoric 
 Acid 
 Lbs. 
 
 White oak 
 Red oak . 
 Ash . . 
 Pine . . 
 Georgia pine 
 Dogwood . 
 
 254. Action of Ashes on Soils. — Ashes act upon soils 
 both chemically and physically. They are usually re- 
 garded as a potash fertilizer only, but they also contain 
 lime and phosphoric acid, and may be very beneficial 
 in supplying these elements. The potash is present 
 mainly as potassium carbonate. Ashes are valuable, 
 too, because they add alkaline matter to the soil, which 
 corrects acidity and aids nitrification. A dressing of 
 ashes improves the mechanical condition of many soils 
 by binding together the soil particles. This property 
 is well illustrated in the so-called Gumbo soils, which 
 contain so much alkaline matter that the soil has a soapy 
 taste and appearance, and when plowed the particles fail 
 to separate. 
 
 255. Leached Ashes. — When ashes are leached the 
 soluble salts are extracted; the insoluble matter which 
 is left is composed mainly of calcium carbonate and 
 silica.*^*^ 
 
220 
 
 SOILS AND FERTILIZERS 
 
 Water 
 
 Silica, etc. . . . 
 Potassium carbonate 
 Calcium carbonate . 
 Phosphoric acid . . 
 
 Unleached Ashes 
 
 Leached Ashes 
 
 Per Cent 
 
 Per Cent 
 
 I2.0 
 
 30.0 
 
 13.0 
 
 13.0 
 
 5-5 
 
 I.I 
 
 61.0 
 
 51.0 
 
 1.9 
 
 1.4 
 
 256. Alkalinity of Leached and Unleached Ashes. — 
 
 A good way to detect leached ashes is to determine the 
 alkalinity in the following way : weigh out 2 grams of 
 ashes into a beaker, add 100 cc. distilled water, and 
 heat on a sand bath nearly to boiling, cool and filter. 
 To 50 cc. of the filtrate add about 3 drops of cochineal 
 indicator, and then a standard solution of hydrochloric 
 acid from a burette until the solution is neutral. If a 
 standard solution of acid cannot be procured, one con- 
 taining 15 cc. concentrated hydrochloric acid per liter 
 of distilled water may be used for comparative pur- 
 poses. Leached ashes require less than 2 cc. of acid 
 to neutrahze the alkaline matter in i gram, while un- 
 leached ashes require from 10 to 18 cc. In purchasing 
 wood ashes, if a chemical analysis cannot be secured, 
 the alkalinity of the ash should be determined. 
 
 257. Coal and Other Ashes. — Since the amount of 
 phosphoric acid and potash in coal ashes is very small, 
 they have httle fertilizer value. Soft coal ashes contain 
 
POTASH FERTILIZERS 
 
 221 
 
 more potash than those from hard coal, but it is held in 
 such firm combination as to be of but little value. 
 
 The ashes from sawmills where soft wood is burned, 
 and they are unprotected, are nearly worthless. When 
 peat bogs are burned over, large amounts of ashes are 
 produced. If the bogs were covered with timber, the 
 ashes are sometimes of sufficient value to warrant their 
 transportation and use. 
 
 Hard coal ashes .... 
 Soft coal ashes . . . . , 
 Sawmill ashes ^* . . . . , 
 Peat bog ashes ^'^ . . . . 
 Peat bog ashes (timbered) ^^ 
 Tobacco stem ash ... 
 Cottonseed hulls, ash . . 
 
 Phosphoric 
 
 Acid 
 Per Cent 
 
 258. Commercial Value of Potash. — The market value 
 of potash is governed by the selling price of high-grade 
 sulphate of potash and kainit. Ordinarily, it varies 
 from 4 to 5 cents per pound. As in the case of nitro- 
 gen and phosphoric acid, the market and field values, 
 as determined by crop yields, may be entirely at vari- 
 ance. Before potash salts are used, careful field tests 
 should be made to determine the actual condition of the 
 soil as to its need of potash. (See Chapter X, Commer- 
 cial Fertilizers.) 
 
222 SOILS AND FERTILIZERS 
 
 259. Use of Potash Fertilizers. — Wood ashes or 
 Stassfurt salts should not be used in excessive amounts. 
 Not more than 300 pounds per acre should be applied 
 unless the soil is known to be markedly deficient in 
 potash, and previous tests indicate that larger amounts 
 are safe and advisable. Potash fertilizers should be 
 evenly spread and not allowed to come in direct con- 
 tact with plant roots, and should be used early in the 
 spring before seeding or before the crop has made 
 much growth. Wood ashes make an excellent top 
 dressing for grass lands, particularly where it is de- 
 sired to encourage the growth of clover. There are 
 but few crops or soils that are not greatly benefited 
 by a light application of wood ashes, and none should 
 ever be allowed to leach or waste about a farm. 
 
 260. Joint Use of Lime and Potash. — When a potash 
 fertilizer is used, a dressing of lime will frequently be 
 found beneficial. The potash undergoes fixation, and 
 when it is liberated there should be some basic material 
 as lime to take its place. Goessmann observed that 
 land manured for several years with potassium chlo- 
 ride finally produced sickly crops, but an application 
 of slaked lime restored a healthy appearance to suc- 
 ceeding crops.^'' If the soil is well stocked with lime, 
 its joint use with potash fertilizers is not necessary. 
 If it is acid, lime should be used to correct the acidity 
 before the potash is applied. The use of potash fer- 
 tilizers for special crops is discussed in Chapter X. 
 
CHAPTER IX 
 LIME AND MISCELLANEOUS FERTILIZERS 
 
 261. Calcium an Essential 
 Element of Plant Food. — Cal- 
 cium is present in the ash of 
 all plants, and is usually more 
 abundant in soils than phos- 
 phorus or potassium. It takes 
 an essential part in plant 
 growth, and whenever with- 
 held growth is checked. The 
 effect of withholding calcium 
 is shown in the illustration 
 (Fig. 43), which gives the 
 total growth made by an oat 
 plant under such a condition. 
 
 Plants grown on soils defi- 
 cient in calcium compounds 
 lack hardiness. They are not 
 so able to withstand drought 
 or unfavorable climatic condi- 
 tions as plants grown on soils 
 well supplied with this element. 
 Calcium does not accumulate 
 in the seeds of plants, but is 
 present mainly in the leaves 
 
 Fig. 43. 
 
 Oat Plant grown with- 
 out Calcium. 
 
224 
 
 SOILS AND FERTILIZERS 
 
 and stems, where it takes an important part in the pro- 
 duction of new tissue. The term ' lime/ when used in 
 connection with crops and soils, refers to their content 
 of calcium oxid, CaO. 
 
 262. Amount of Lime removed in Crops. 
 
 38 
 
 Pounds per Acre 
 CaO 
 
 Wheat, 2o bushels 
 Straw, 2000 pounds 
 
 Total 
 Corn, 65 bushels . 
 Stalks, 3000 pounds 
 
 Total 
 Peas, 30 bushels . 
 Straw, 3500 pounds 
 
 Total 
 Flax, 15 bushels . 
 Straw, 1800 pounds 
 
 Total 
 Clover, 4000 pounds 
 
 I 
 
 _7 
 8 
 
 I 
 
 II 
 12 
 
 4 
 
 ZL 
 
 75 
 3 
 
 _y 
 16 
 
 75 
 
 Clover and peas remove so much lime from the soil 
 that they are often called lime plants. The amount 
 required by grain and hay is small compared with that 
 required by a clover or pea crop. 
 
 263. Amount of Lime in Soils. — There is no other 
 element in the soil in such variable amounts as cal- 
 cium, popularly called lime. It may be present from 
 
LIME AND MISCELLANEOUS FERTILIZERS 22 5 
 
 one hundredth of a per cent to 20 per cent or 
 more. Soils which contain from 0.3 to 0.5 per cent, 
 as carbonate, are usually well supphed. The lime in 
 a soil takes an important part in soil fertility ; when 
 it is wanting, humic acid may be formed, nitrification 
 checked, and the soil particles will lack binding mate- 
 rial. Calcium carbonate is somewhat soluble in soil 
 water, due to the presence of carbon dioxide. Waters 
 are hard because of the presence of lime. The loss of 
 lime by leaching has caused many soils to become 
 unproductive. 
 
 264. Different Kinds of Lime Fertilizers. — By the 
 
 term * lime fertilizer ' is usually meant land plaster 
 (CaS04, 2 H2O). Occasionally quicklime (CaO) and 
 slaked Hme (Ca[OH]2) are used on very sour land. In 
 general, a lime fertilizer is one which supplies the ele- 
 ment calcium ; common usage, however, has restricted 
 the term to sulphate of lime. 
 
 j 
 
 i 265. Action of Lime Fertilizers upon Soils. — Lime 
 
 1 fertilizers act both chemically and physically. Chemi- 
 
 j cally, Hme unites with the organic matter to form 
 
 humate of lime and thus prevents the formation of 
 I humic acid. It also aids in nitrification and acts upon 
 j the soil, liberating potassium and other elements of plant 
 
 food. Physically, lime improves capillarity, precipitates 
 I clay when suspended in water, and prevents losses, as 
 ! the washing away of fine earth. When soils are defi- 
 Q 
 
226 
 
 SOILS AND FERTILIZERS 
 
 cient in lime, an acid condition may develop to such 
 an extent as to be injurious to vegetation. Nitrogen, 
 phosphoric acid, and potash may all be present in liberal 
 amounts, but in the absence of lime poor results are 
 obtained. Because of the loss by drainage, removal 
 as plant food and the chemical reaction in which it 
 takes a part, there is greater necessity for a liberal 
 supply of active lime compounds in a soil than of any 
 other element of plant food. 
 
 266. Lime liberates Potash. — The action of lime 
 upon soils well stocked with potash results in fixation 
 of the lime and liberation of the potash ; the reaction 
 takes place in accord with the well-known exchange of 
 bases explained in the chapter on fixation. The extent 
 to which potash may be liberated by lime depends upon 
 the firmness of chemical combination with which the 
 potash is held in the soil. Boussingault found that 
 when clover was limed there was present in the crop 
 three times as much potash as in a similar crop not 
 limed. His results are as follows :^^ 
 
 Lime . . . . 
 Potash . . . , 
 Phosphoric acid 
 
 Kilos per Hectare 
 
 In Crop not Ltmed 
 
 First 
 
 year 
 
 32.2 
 26.7 
 II.O 
 
 Second 
 year 
 
 •52.2 
 
 28.6 
 
 7.0 
 
 In Limed Crop 
 
 First 
 year 
 
 794 
 95.6 
 24.2 
 
 Second 
 year 
 
 102.8 
 97.2 
 22.9 
 
LIME AND MISCELLANEOUS FERTILIZERS 22/ 
 
 The indirect action of land plaster upon western 
 prairie soils in liberating plant food, particularly potash 
 and phosphoric acid, is unusually marked. Laboratory 
 experiments show that small amounts of gypsum are 
 quite active in rendering potash, phosphoric acid, and 
 even nitrogen soluble in the soil water. '^ Occasionally 
 applications of superphosphate fertilizers give large 
 yields, due to the gypsum which they contain, and not 
 to the phosphorus. 
 
 267. Quicklime and Slaked Lime. — When it is de- 
 j sired to correct acidity, slaked lime is used. Air-slaked 
 I lime is not so valuable as water-slaked lime. Quick- 
 ' lime cannot be used on land after a crop has been 
 1 seeded. Both slaked lime and quicklime should be 
 i applied some little time before seeding, and not to the 
 \ crop. The action of quicklime upon organic matter 
 ' is so rapid that it destroys vegetation. Slaked lime is 
 ■ less injurious to vegetation. 
 
 I 268. Pulverized Lime Rock. — In some localities pul- 
 ] verized hme rock is used. It may be applied as a top 
 I dressing in almost unlimited amounts. It is most 
 J beneficial on light, sandy soils, where it performs the 
 I function of fine clay as well as promoting chemical 
 : action. Acid soils also are benefited by its use. Not 
 I all soils are alike responsive to applications of lime- 
 I stone, and before using it is best to determine to what 
 I extent it is needed. There are no ordinary conditions 
 
228 SOILS AND FERTILIZERS 
 
 where limestone is injurious to soil or crop, and it is 
 frequently most helpful. 
 
 269. Marl. — Underlying beds of peat, deposits of 
 marl are occasionally found. Marl is a mixture of 
 disintegrated limestone and clay, and contains variable 
 amounts of calcium carbonate, phosphoric acid, and 
 potash. When peat and marl are found together, they 
 may be used jointly with manure as described in Sec- 
 tion 182. Many sandy lands in the vicinity of peat 
 and marl deposits would be greatly improved, both 
 physically and chemically, by these materials. 
 
 270. Physical Action of Lime. — The addition of lime 
 fertilizers to sandy soils improves their general physi- 
 cal condition. Heavy clays lose their plasticity when 
 limed and the fine clay particles are cemented together 
 and act as sand, which improves the mechanical con- 
 dition of the soil. The physical action of lime in soils 
 is well illustrated in the case of ' loess soils,' which are 
 composed of clay and limestone. The lime cements 
 together the clay particles to form compound grains, 
 making the soil more permeable and more easily tilled. 
 The better physical 'condition which follows the appli- 
 cation of lime fertilizers is frequently sufficient to war- 
 rant their use. 
 
 271. Application of Lime Fertilizers. — Lime is gener- 
 ally used as a top dressing on grass lands at the rate of 
 200 to 500 pounds per acre. Excessive applications are 
 
LIME AND MISCELLANEOUS FERTILIZERS 229 
 
 undesirable. Lime as gypsum is particularly valuable 
 when applied to land where crops are grown which 
 assimilate large amounts, as clover and other legumes. 
 It should be remembered that it is not a complete 
 fertilizer, but simply an amendment and an indirect 
 fertilizer.^ If used to excess it may get the soil in such 
 condition that plant food is not easily rendered avail- 
 able. A common saying is, " Lime makes the father 
 rich but the son poor."^^ This is true, however, only 
 when lime is used in excess. When used occasionally 
 in connection with other manures, it has no injurious 
 effect upon the soil and is a valuable fertilizer, especially 
 where clover is grown with difficulty. 
 
 MISCELLANEOUS FERTILIZERS 
 
 272. Salt is frequently used as an indirect fertiHzer. 
 Sodium and chlorine, the two elements of which it is 
 composed, are not absolutely necessary for normal 
 plant growth. When salt is applied to the soil and 
 the sodium undergoes fixation, potassium may be lib- 
 erated. An early experiment of Wolff illustrates this 
 point : a buckwheat plot fertilized with salt produced 
 a crop with more potash and less sodium than a similar 
 unfertilized plot. 
 
 Salt may be used to check the rank growth of straw 
 during a rainy season, and thus prevent loss of the 
 crop by lodging, although not in excessive amounts, as 
 it is destructive to vegetation ; 200 pounds per acre is a 
 
230 SOILS AND FERTILIZERS 
 
 fair application. Salt also improves the physical con- 
 dition of the soil by increasing the surface tension of 
 the soil water. It should not be used on a tobacco or 
 potato crop, because it injures the quality of the product. 
 Salt is beneficial in preventing some forms of fungous 
 diseases from becoming established in soils. 
 
 273. Magnesium Salts. — Magnesium is present in the 
 ash of all plants, and is an element essential for plant 
 growth. Usually soils are so well stocked with mag- 
 nesium that it is not necessary to apply it in ferti- 
 lizers. Some of the magnesium salts, as the chloride, 
 are injurious to vegetation, but when associated with 
 lime as carbonate, magnesia imparts fertility. In many 
 of the Stassfurt salts, magnesium is found. 
 
 274. Soot. — The deposits formed in boiler flues and 
 chimneys when wood and soft coal are burned contain 
 small amounts of potash and phosphoric acid. Soot is 
 valuable mainly as a mechanical fertilizer and is slow 
 in decomposing. It contains but little plant food as 
 shown by the following analysis : 
 
 Potash . . . 
 Phosphoric acid 
 
 Soft Coal Soot 
 Per Cent" 
 
 0.84 
 0.75 
 
 Hard Wood Soot 
 Per Cent™ 
 
 1.78 
 0.96 
 
 275. Seaweeds. — Seaweeds are rich in potash and 
 near the seacoast are extensively used for fertilizer. 
 
LIME AND MISCELLANEOUS FERTILIZERS 23 1 
 
 Composition of 
 
 Mixed Seaweeds 
 
 Per Cent™ 
 
 Water . . . . 
 Nitrogen . . . 
 Potash . . . . 
 Phosphoric acid 
 
 81.50 
 
 0.73 
 1.50 
 0.18 
 
 Weeds and plants produced on waste land along the 
 sea are in some European countries burned and the 
 ashes used as fertilizer. By this means waste land is 
 made to produce fertilizer for fields which are tillable. 
 
 276. Weeds. — The amount of fertility removed in 
 weeds is usually more than in agricultural plants, be- 
 cause weeds have greater power of obtaining food from 
 the soil. When wheat or other grain is raised, and a 
 small crop of grain and a large crop of weeds are the 
 result, there is more fertility removed from the soil than 
 if a heavy stand of grain had been obtained. The ashes 
 of strand plants and weeds are extremely variable in 
 composition. 
 
 277. "Wool Washings and Waste. — The washings from 
 wool contain sufficient potash to make them valuable as 
 fertilizer. In wool there is a high per cent of potash, 
 which is soluble and readily removed in the washings. 
 Wool waste may contain from i to 5 per cent of potash 
 and from 4 to 7 per cent of nitrogen in a somewhat 
 inert form. 
 
232 SOILS AND FERTILIZERS 
 
 278. Street Sweepings. — The horse manure and de- 
 bris collected from paved streets in cities and known 
 as street sweepings have some value as fertilizer, and 
 are occasionally used for market gardening purposes. 
 Street sweepings, because of the loss of the liquid 
 excrements, have a lower value than average stable 
 manure and cannot be used economically when labor 
 and the cost of hauling are high-priced, or when a 
 quick-acting manure is desired. For sanitary reasons, 
 the use of street sweepings is not always desirable, as 
 mixed with the horse droppings frequently are associ- 
 ated accumulations of filth from dwellings contaminated 
 with disease germs. Crude garbage has a low manurial 
 value ; when sorted and cremated, the burned residue 
 can be used to better advantage as fertilizer than the 
 raw garbage, and is without the objectionable and un- 
 sanitary features. 
 
CHAPTER X 
 COMMERCIAL FERTILIZERS AND THEIR USE 
 
 279. Development of the Commercial Fertilizer Indus- 
 try. — The commercial fertilizer industry owes its origin 
 to Leibig's work on plant ash. The first superphos- 
 phate was made by Sir J. B. Lawes about 1840, from 
 spent bone black and sulphuric acid. His interest had 
 previously been attracted to the use of bones as fer- 
 tilizer by a gentleman who farmed near him, " who 
 pointed out that on one farm bone was invaluable for 
 the turnip crop, and on another farm it was useless."** 
 
 Since i860 the commercial fertilizer industry in this 
 country has developed rapidly, until now large sums of 
 money are annually expended in purchasing commercial 
 fertilizers and amendments, and nearly all in less than 
 a third of the area of the United States. 
 
 280. Complete Fertilizers and Amendments. — The 
 
 term ' commercial fertihzer ' is applied to materials made 
 by mixing different substances which contain plant 
 food in concentrated forms. When a commercial fer- 
 tilizer contains nitrogen, phosphoric acid, and potash, 
 it is called a complete fertilizer, because it supplies the 
 three elements which are liable to be most deficient. 
 
 233 
 
234 SOILS AND FERTILIZERS 
 
 Materials as sodium nitrate which supply only one ele- 
 ment are called amendments. It frequently happens 
 that a soil requires only one element in order to produce 
 good crops, and in such cases only the one element 
 needed should be supplied. 
 
 Complete fertilizers are often used when the soil is 
 in need of an amendment only. 
 
 281. Variable Composition of Commercial Fertilizers. 
 — Since commercial fertilizers are made by mixing 
 various materials which contain different amounts of 
 nitrogen, phosphoric acid, and potash, it follows they 
 are extremely variable in composition and value. No 
 two samples are the same, hence the importance of 
 knowing the composition of every brand purchased. 
 The composition of fertilizers is varied to meet the 
 requirements of different soils and crops. Some ferti- 
 lizers are made rich in phosphoric acid, while others are 
 rich in nitrogen and potash. 
 
 282. How a Fertilizer is Made. — The most common 
 materials used in making complete fertilizers are : ni- 
 trate of soda, kainit, and dissolved phosphate rock. 
 These materials have about the following composition : 
 
 Nitrate of soda 15.5 per cent nitrogen. 
 
 Kainit 12.5 per cent potash. 
 
 Dissolved phosphate . . . 14.0 per cent phosphoric acid 
 
 The fertilizer may be made rich or poor in any ingre- 
 dient. Many fertilizers contain about twice as much 
 
COMMERCIAL FERTILIZERS AND THEIR USE 235 
 
 potash as nitrogen and five times as much phosphoric 
 acid as potash. In order to make a ton of such a ferti- 
 Hzer it would be necessary to take : 
 
 Pounds 
 
 Nitrate of soda 
 Kainit . . . 
 Phosphate . . 
 
 225 
 
 425 
 
 1350 
 
 The ton of fertihzer would contain about 35 pounds 
 of nitrogen, 189 pounds of phosphoric acid, and 53 
 pounds potash. These amounts are determined by 
 multiplying the percentage composition by the weight 
 of material taken : 
 
 Pounds 
 
 Nitrogen 225 x 0.155 = 34.9 
 
 Potash 425 X 0.125 = 53-' 
 
 Phosphoric acid 1350 x 0.14 = 189.0 
 
 The fertilizer would contain about 1.75 per cent ni- 
 trogen, 2.65 per cent potash, and 9.45 per cent phos- 
 phoric acid. The percentage amounts are obtained by 
 dividing the total pounds by 20. This fertilizer if made 
 at home from materials purchased in the market, at the 
 prices indicated, would cost, exclusive of transportation 
 and mixing, about $21.47. 
 
 Pounds Cost 
 
 Nitrogen 34.9 @ 16 cents = $5.58 
 
 Phosphoric acid .... 189.0 @ 7 cents = 13.23 
 Potash 53-1 @ 5 cents = 2.66 
 
 Total $21.47 
 
236 SOILS AND FERTILIZERS 
 
 A more concentrated fertilizer could be prepared by 
 using high-grade sulphate of potash, superphosphate, 
 and ammonium sulphate. A fertilizer composed of 
 these ingredients would contain : 
 
 b 
 
 O 
 
 O O K 
 
 ^ES 
 
 WgS 
 u ^ h 
 
 Pounds Per Cent t„^ Value wow 
 
 L,BS. PmU&h 
 
 300 Sulphate of ammonia 20 N 60 @ 16 cents = $ 9.60 3.00 
 
 500 Sulphate of potash . 50 KjO 250 @ 5 cents = 12.50 12.50 
 
 1200 Superphosphate . . 35 P^O^ 420 @ 7 cents = 29.40 21.00 
 
 Total $51.50 
 
 So concentrated a fertilizer as the preceding is rarely, 
 if ever, found on the market, although the price, ^51.50 
 per ton, is frequently charged. This example shows 
 the composition and cost of the ingredients in one 
 of the most concentrated fertilizers that can be pro- 
 duced. 
 
 The market value of the materials of which commer- 
 cial fertilizers are made fluctuates Hke that of other com- 
 modities. 
 
 Any of the different materials mentioned in the 
 chapters on special fertilizers can be used in making 
 commercial fertilizers, as dried blood, tankage, nitrate 
 of soda, sulphate of ammonia, raw bone, dissolved 
 bone, raw phosphate rock, dissolved phosphate rock, 
 basic slag, kainit, muriate or sulphate of potash, and 
 many others. Inasmuch as each of these materials 
 has a different value, it follows that fertilizers, even 
 
COMMERCIAL FERTILIZERS AND THEIR USE 23/ 
 
 of the same general composition, may have widely 
 different crop-producing powers. 
 
 283. Inert Forms of Plant Food in Fertilizers. — A 
 
 fertilizer of the same general composition as the first 
 example, but of different availability of the elements, 
 could be made from feldspar rock, apatite rock, and 
 leather. The leather contains nitrogen, the apatite 
 contains phosphoric acid, and the feldspar, potash. 
 Such a fertilizer would have no value when used on a 
 crop, because all the plant food elements are present 
 in unavailable forms. Hence, in purchasing fertilizers, 
 it is necessary to know not only the percentage com- 
 position, but also the nature of the materials from which 
 the fertilizer was made. Inert forms of plant food are 
 akin to indigestible forms of animal food ; it is the food 
 which is assimilated that is of value whether it be by 
 animals or by plants. 
 
 284. Inspection of Fertilizers. — In many states, laws 
 have been enacted regulating the manufacture and sale 
 of commercial fertilizers, and provision is made for 
 inspection and analysis of all brands offered for sale. 
 The label on the fertilizer package must specify the 
 percentage amounts of available nitrogen, phosphoric 
 acid, and potash. Inspection has been found necessary 
 in order to protect the farmer and the honest manu- 
 facturer. As the result of inspection and analysis, 
 occasionally a fraud is revealed like the following : ''^ 
 
238 SOILS AND FERTILIZERS 
 
 Natural Plant Food, $25 to $28 per Ton 
 
 Composition 
 
 Total phosphoric acid 
 
 Insoluble phosphoric acid 
 
 Available phosphoric acid . . . . 
 
 Potash soluble in water 
 
 Actual value per ton, $1.52 
 
 285. Mechanical Condition of Fertilizers. — In pur- 
 chasing a fertilizer its mechanical condition should be 
 considered. The finer the fertiUzer, as a rule, the bet- 
 ter it is for promoting crop growth. Some combina- 
 tions of plant food produce fertilizers which become so 
 hard and lumpy that it is difficult to crush them before 
 spreading. They should be pulverized so they may be 
 evenly distributed, otherwise the plant food will not be 
 economically used. A fertilizer that passes through a 
 sieve with holes 0.25 mm. in diameter is more valuable 
 and can be used to better advantage than one of the 
 same composition with particles 0.5 mm. in size. 
 
 286. Forms of Nitrogen in Commercial Fertilizers. — 
 
 Nitrogen is present in commercial fertilizers in three 
 forms : (i) Ammonium salts, (2) nitrates, and (3) 
 organic nitrogen. The organic nitrogen is divided 
 into two classes: (a) available, and (d) unavailable. 
 Pepsin and also potassium permanganate are used as 
 solvents for determining the availability of the organic 
 
COMMERCIAL FERTILIZERS AND THEIR USE 
 
 239 
 
 nitrogen. The relative values of the different forms 
 of nitrogen are discussed in Chapter IV. Three fer- 
 tilizers may have the same amount of total nitrogen 
 and still have entirely different crop-producing powers. 
 
 Nitrogen as : 
 
 Ammonium compounds 
 Nitrates ...... 
 
 Organic nitrogen : 
 
 Soluble ■ 
 
 Insoluble 
 
 Total . . . 
 
 No. I 
 Per Cent 
 
 0.15 
 
 No. 2 
 Per Cent 
 
 0.25 
 0.15 
 
 1.25 
 0-35 
 
 No. 3 
 Per Cent 
 
 O.IO 
 O.IO 
 
 0.55 
 1.25 
 
 In purchasing fertilizers it is important to know not 
 only the amount of nitrogen, but also the form in 
 which it is present. In No. 3 the nitrogen is in an 
 inert form as in leather, while in No. 2 it is largely in 
 the form of dried blood, and No. i has mainly am- 
 monium compounds. Each of these fertilizers, as ex- 
 plained in the chapter on nitrogenous manures, has a 
 different plant food value. 
 
 287. Phosphoric Acid. — There are three forms of 
 phosphoric acid "in commercial fertilizers: (i) water 
 soluble, (2) citrate-soluble, and (3) insoluble. The 
 water and citrate-soluble are called the available phos- 
 phoric acid. In most fertilizers the phosphoric acid is 
 derived from dissolved phosphate rock and is in the 
 
240 
 
 SOILS AND FERTILIZERS 
 
 form of monocalcium phosphate. The citrate-soluble 
 is mainly dicalcium phosphate with variable amounts 
 of iron and aluminum phosphates in easily soluble 
 forms. The insoluble phosphoric acid is tricalcium 
 and other phosphates, as iron and aluminum, which 
 are soluble only in strong mineral acids. The insoluble 
 phosphoric acid in fertilizers is considered as having 
 but little value. As in the case of nitrogen, three 
 fertihzers may have the same total amount of phos- 
 phoric acid and yet have entirely different values. 
 
 
 
 No. I 
 Per Cent 
 
 No. 2 
 Per Cent 
 
 No. 3 
 Per Cent 
 
 Water-soluble phosphoric acid . . . 
 Citrate-soluble phosphoric acid . . . 
 Insoluble 
 
 8.00 
 1.50 
 0.50 
 
 0.25 
 
 8.00 
 175 
 
 0.25 
 
 0.75 
 
 9.00 
 
 
 Total 
 
 10.00 
 
 10.00 
 
 10.00 
 
 
 
 No. 3 has little value ; it contains insoluble phos- 
 phate rock or some material of the same nature. No. i 
 is the most valuable, because it contains dissolved 
 phosphate rock or dissolved bone and but little insoluble 
 phosphoric acid. No. 2 is composed of such materials 
 as the best grade of basic slag or roasted aluminum 
 phosphate or fine steamed bone. 
 
 288. Potash. — The three forms of potash in fertili- 
 zers are: (i) water-soluble, (2) acid-soluble, and (3) in- 
 soluble. Sulphate of potash, kainit, and muriate of 
 
COMMERCIAL FERTILIZERS AND THEIR USE 241 
 
 potash are soluble in water and belong to the first class. 
 In some states the fertilizer laws recognize only the 
 water-soluble potash. In the second class are found 
 materials like tobacco stems and other organic forms of 
 potash. Substances like feldspar, which contain insol- 
 uble potash, are of no value in fertilizers. As a rule, 
 the potash in commercial fertilizers is soluble in water ; 
 in only a few cases are acid-soluble forms met with. 
 Insoluble potash is considered an adulterant. 
 
 289. Misleading Statements on Fertilizer Packages. — 
 
 Occasionally the percentage amounts of nitrogen, phos- 
 phoric acid, and potash are stated in misleading ways : 
 as ammonia, sulphate of potash, and bone phosphate of 
 lime. Inasmuch as ammonia contains 14 parts nitro- 
 gen and 3 parts by weight of hydrogen, it follows the 
 ammonia content is proportionally greater than the 
 nitrogen content, because of the additional hydrogen 
 carried by the ammonia. And so with sulphate of 
 potash, which contains about 50 per cent potash and 50 
 per cent of sulphuric anhydride. This method of stat- 
 ing the composition can be considered in no other way 
 than as a fraud, especially when the fertilizer contains 
 no sulphate of potash, but cheaper materials, and the 
 phosphoric acid is not derived from bone. 
 
 290. Estimated Commercial Value of Fertilizers. — 
 
 The estimated value of a commercial fertilizer is ob- 
 tained from the percentage composition and the trade 
 
242 SOILS AND FERTILIZERS 
 
 value of the materials used. Suppose two fertilizers 
 are selling at $28 and $35, respectively, each having a 
 different composition, the estimated value of each could 
 be obtained in the following way : 
 
 Composition of Fertilizers 
 
 No. I No. 2 
 
 Selling Price $28 Selling Price $35 
 
 Per Cent Per Cent 
 
 Nitrogen as nitrates 1.50 2.10 
 
 Phosphoric acid, available . . .8.00 10.00 
 
 Phosphoric acid, insoluble . . . 2.00 0.50 
 
 Potash (water-soluble) .... 2.00 3.50 
 
 Pounds per Ton 
 
 No. I No. 2 
 
 Nitrogen . . . 1.50 x 20 = 30 2.10 x 20 = 42 
 
 Phosphoric acid . 8.00 x 20 = 160 10.00 x 20 = 200 
 Potash .... 2.00 x 20 = 40 3.50 X 20 = 70 
 
 Estimated Value 
 
 No. I 
 Nitrogen . . . . 30 x 0.16 = $ 4.80 
 Phosphoric acid . . 160 x 0.07 = 11.20 
 Potash 40 X 0.05 = 2.00 
 
 $18.00 
 Difference between estimated value and selling price 
 $10.00 ; No. 2, $10.78. 
 
 The trade value of a commercial fertilizer often varies 
 widely from the actual or crop-producing value, for in j 
 assigning a trade value simply the cost of the ingredi- 1 
 ents is considered, and this is not necessarily identical 
 
 
 No. 2 
 
 42 X 0.16 
 
 = $ 6.72 
 
 :oo X 0.07 
 
 = 14.00 
 
 70 X 0.05 
 
 = 3-5° 
 
 
 $24.22 
 
 ing price : 
 
 No. I, 
 
COMMERCIAL FERTILIZERS AND THEIR USE 
 
 243 
 
 with the actual value secured in increased yield from 
 the use of the fertilizer. 
 
 291. Home Mixing of Fertilizers. — At the New 
 Jersey Experiment Station it was shown that "the 
 charges of the manufacturers and dealers for mixing, 
 bagging, shipping, and other expenses are on the aver- 
 age $8.50 per ton, and also that the average manu- 
 
 FlG. 44. Composition of Fertilizers. 
 
 factured fertiUzer contains about 300 pounds of actual 
 fertilizing constituents per ton. These figures are prac- 
 tically true of other states, where large quantities of 
 commercial fertilizers are used."'^^ In states where 
 smaller amounts are used the difference between the 
 estimated cost and selling price is greater than $8.50. 
 
 These facts emphasize the economy of home mixing. 
 The difference in price between the raw materials and 
 the product sold is frequently so great that it is an ad- 
 vantage for the farmer to purchase the raw materials, 
 as sulphate of potash, nitrate of soda, and acid phos- 
 
244 
 
 SOILS AND FERTILIZERS 
 
 phate, and mix them as desired. By so doing fertilizers 
 of any composition may be prepared and there is less dan- 
 ger of securing an inferior article. Of course it is not 
 possible by means of shovels and sieves to accomplish as 
 thorough mixing of the ingredients as with machinery. 
 
 Nitrate of soda . 
 Acid phosphate . 
 Sulphate of potash 
 
 Formula No. i 
 
 Pounds 
 
 500 containing nitrogen . 
 
 . 1200 containing phos. acid . 
 
 , 300 containing potash . . 
 
 Total 
 
 Nitrate of soda 
 Acid phosphate . 
 Sulphate of potash 
 Plaster, etc. . . 
 
 Total . . 
 
 Formula No. 3 
 200 containing nitrogen 
 1500 containing phos. acid 
 1 50 containing potash . 
 150 
 
 Pounds 
 
 77-5 
 168.0 
 
 150.0 7.50 
 
 3897 
 
 316.0 
 
 w z 
 
 o o « 
 2h« 
 
 b: S es 
 u o H 
 
 3-87 
 8.40 
 
 Total . . . 
 
 Formula No. 2 
 
 • 395-5 
 
 
 Nitrate of soda . , 
 
 , 250 containing nitrogen . 
 
 • 38.7 
 
 1-99 
 
 Acid phosphate . . 
 
 . 900 containing phos. acid . 
 
 . 126.0 
 
 6.30 
 
 Sulphate of potash , 
 
 , 450 containing potash . . 
 
 . 225.0 
 
 11.50 
 
 Plaster, etc. . . 
 
 . 400 
 
 
 
 3L0 
 
 I-5S 
 
 210.0 
 
 10.50 
 
 75.0 
 
 5-75 
 
 292. Fertilizers and Tillage. — Commercial fertilizers 
 cannot be made to take the place of good tillage, which 
 is equally as important when fertilizers are used as when 
 
COMMERCIAL FERTILIZERS AND THEIR USE 245 
 
 they are omitted. Scant crops are as frequently due to 
 the want of proper tillage as to the absence of plant 
 food. Poor cultivation results in getting the soil out of 
 condition ; then, instead of thoroughly preparing the 
 land, commercial fertilizers are resorted to, and the 
 conclusion is reached that the soil is exhausted, when in 
 reality it is suffering for the want of cultivation, for a 
 dressing of land plaster, for farm manures, or for a 
 change of crops. There is no question but what Better 
 tillage, better care and use of farm manures, culture of 
 clover and systematic rotation of crops would result in 
 greatly reducing the amount annually spent for com- 
 mercial fertilizers, without reducing the yield of crops, 
 as well as securing larger returns for the fertilizers used. 
 In general, the better the cultivation the less the amount 
 of commercial fertihzer required for average farm crops. 
 Cultivation cannot, however, entirely take -the place of 
 fertilizers. 
 
 293. Abuse of Commercial Fertilizers. — When a soil 
 produces poor crops, a complete fertilizer is frequently 
 used where only an amendment is needed. Restricted 
 crop production on long-cultivated prairie soils is often 
 due to poor physical condition, deficiency of humus and 
 availalDle nitrogen, or, in some cases, to lack of a mineral 
 element as potash or phosphoric acid. If the nitrogen 
 is supplied by legumes, and the one element of fertility 
 needed is added, improved cultivation together with the 
 chemical action of the humus on the minerals of the soil 
 
246 SOILS AND FERTILIZERS 
 
 will generally furnish the necessary, available plant 
 food. Instead, however, of providing the one element 
 needed, others which may already be present in the soil 
 in liberal amounts are often supplied at an unnecessary 
 expense, instead of being made available by cultivation. 
 Another abuse of fertilizers is their application to the 
 wrong crop. A heavy application of potash fertilizer to 
 a wheat crop grown on a rich clay soil, or of nitrate of 
 soda on land seeded to clover, or of land plaster to flax 
 grown on a limestone soil, would be a waste of money. 
 
 294. Judicious Use of Fertilizers. — In order to make 
 the best use of commercial fertilizers, both the soil and 
 the crop must be carefully considered. All soils do not 
 alike respond to commercial fertilizers, and farm crops 
 possess different powers of assimilating food ; turnips, 
 for example, have very restricted power of phosphate 
 assimilation, hence they require phosphate manures, and 
 wheat may need help in obtaining its nitrogen. A 
 wheat crop will starve for want of nitrogen, while an 
 adjoining corn crop will scarcely feel its need. Wheat 
 has strong power of assimilating potash, while clover 
 has less. Hence in the use of fertilizers the ability of 
 the plant to obtain its food must be considered. A 
 light application of either a special purpose or a com- 
 plete fertilizer at the time of seeding is often advanta- 
 geous, as it encourages plant growth by supplying food 
 when it is most needed. There should be some at this 
 time in a highly available condition for the use of the 
 
COMMERCIAL FERTILIZERS AND THEIR USE 
 
 247 
 
 young plants, after that stored up in the seed has been 
 exhausted, and before they are strong enough to make 
 available their own food. 
 
 Fig. 45. Wheat Plots fertilized in Different Ways. 
 
 (From left to right.) 
 
 Complete Fertilizer (Com.), Phosphate Fertilizer, P. 
 
 Potash Fertilizer, K. Nitrogen Fertilizer, N. 
 
 No Fertilizer, Check. 
 
 Commercial fertilizers may assist in promoting desir- 
 able bacterial changes in soils resulting in the elabo- 
 ration of plant food. Before they are used, however, 
 careful field trials should be made. 
 
 295. Experimental Plots. — A piece of land well tilled 
 and of uniform texture should be used for field trials 
 
248 
 
 SOILS AND FERTILIZERS 
 
 1 
 
 with fertilizers. After preparation for the crop, small 
 plots 1/20 of an acre are staked off. A convenient size 
 is, length 204 feet, width 10 feet 8 inches, area 2176 
 square feet. Between each plot a strip 3 feet wide is 
 left. The plan is to apply one element or a combina- 
 tion of elements to a plot and compare the results with 
 plots differently treated.'^'^ 
 
 296. Preliminary Trial. — It is best to make a prelim- 
 inary trial one year and verify the conclusions the next. 
 In making the tests, eight plots are necessary and fer- 
 tilizers are applied in the following way : 
 
 The first plot receives no fertilizer and is used as the 
 basis for comparison. 
 
 The second plot receives a dressing of 8 pounds nitrate 
 of soda, 16 pounds acid phosphate, and 8 pounds sul- 
 phate or muriate of potash. 
 
 The third plot receives nitrogen and phosphoric 
 acid. 
 
 The fourth plot receives nitrogen and potash. 
 
 The fifth plot receives nitrogen. 
 
 The sixth plot receives phosphoric acid and potash. 
 
 The seventh plot receives potash. 
 
 The eighth plot receives phosphoric acid. 
 
 No fertilizer 
 
 N 
 
 N 
 
 N 
 
 
 P2O5 
 
 P-iOs 
 
 K.2O 
 
 
 KoO 
 
 
 
 I 
 
 2 
 
 3 
 
 4 
 
COMMERCIAL FERTILIZERS AND THEIR USE 
 
 249 
 
 N 
 
 P2O5 
 K2O 
 
 KoO 
 
 P2O5 
 
 5 
 
 6 
 
 7 
 
 8 
 
 Should good results be obtained on plot No. 3, the 
 indications are that there is a deficiency of the two 
 elements, nitrogen and phosphoric acid. An increased 
 yield from No. 4 indicates deficiency of nitrogen and 
 potash. Under such conditions the use of a complete 
 fertihzer would be unnecessary. If No. 5 gives an ad- 
 ditional yield, the soil is in want of nitrogen. From 
 the eight plots it will be seen which of the various ele- 
 ments it is advisable to use. The fertilizers should be 
 applied after the land has been thoroughly prepared and 
 before seeding. Corn is a good crop for the first trial. 
 The number of plots may be increased by using well- 
 prepared stable manure and gypsum on plots 9 and 10, 
 respectively. The second year the results should be 
 verified. 
 
 297. Deficiency of Nitrogen. — If the results indicate 
 a deficiency of nitrogen, select two crops, one as wheat, 
 which is particularly benefited by dressings of nitrogen, 
 and another as corn which has less difficulty in obtain- 
 ing this element. The cultivation of each crop should 
 be that which experience has shown to be the best. On 
 one wheat and one corn plot 8 pounds of nitrate of 
 soda should be used, a plot each of wheat and corn being 
 
250 SOILS AND FERTILIZERS 
 
 left unfertilized. If both the corn and the wheat are 
 benefited by the nitrogen, the soil is in need of this ele- 
 ment. If, however, the wheat responds and the corn 
 does not, the soil is not in great need of nitrogen, but 
 does not contain an abundance in available forms. ' 
 
 298. Deficiency of Phosphoric Acid. — In experiment- 
 ing with phosphoric acid, turnips are grown on two 
 plots and barley on two plots. To one plot of each, 16 
 pounds of acid phosphate are applied. If both crops 
 show additional yields, the soil is in need of available 
 phosphoric acid. If only the turnips respond while the 
 barley is indifferent, the soil contains a fair amount. 
 Barley and turnips are used because there is such a 
 marked difference in their power to assimilate phosphoric 
 acid. 
 
 299. Deficiency of Potash. — In order to determine the 
 condition of the soil as to potash, potatoes and oats 
 may be used as the trial crops, and 8 pounds of sulphate 
 of potash should be applied to one plot of each. Addi- 
 tional yields indicate a poverty of available potash ; an 
 increased potato crop and an indifferent oat crop indicate 
 potash not in the most available form. If no additional 
 yields are obtained with either crop, the soil is not in 
 need of potash. 
 
 300. Deficiency of Two Elements. — If the preliminary 
 trial indicates a deficiency of two elements, as nitrogen 
 and phosphoric acid, in verifying these results, both 
 
COMMERCIAL FERTILIZERS AND THEIR USE 2$! 
 
 elements are used together, in the same way as de- 
 scribed for deficiency of nitrogen, with additional plots 
 for the separate application of nitrogen and phosphoric 
 acid. 
 
 301. Importance of Field Trials. — While it is a diffi- 
 cult matter to determine the actual needs of a soil, it 
 will be found that both time and money are saved by a 
 systematic study of the question. Suppose fertilizers 
 are used in a ' hit or miss ' way year after year on a 
 soil deficient only in phosphoric acid, it might take eight 
 years to indicate what the soil really lacks if a different 
 fertilizer is used each year, and during all this period 
 either the soil fails. to receive its proper fertilizer, or 
 expensive and unnecessary plant food is provided. 
 Field tests to be of value must be continued for a num- 
 ber of years and the results verified. 
 
 302. Will it pay to use Commercial Fertilizers? — 
 
 This question can be answered only by trial. If a soil 
 is in need of available plant food, the additional yield 
 should pay for the fertihzer and the expense of using 
 it. Some fertilizers have an influence on two or three 
 successive crops, and only partial returns are received 
 the first year. When large crops must be produced on 
 small areas, as in truck farming, commercial fertilizers 
 are generally necessary. They have not yet been ex- 
 tensively used in the western prairie states in the pro- 
 duction of large tracts of staple crops, as wheat and corn. 
 
252 SOILS AND FERTILIZERS f 
 
 If there is a good stock of natural fertility in the soil 
 and it is well tilled, with farm manures used and the 
 crops systematically rotated, commercial fertilizers will 
 not be needed. With poor cultivation and a soil that 
 has been impoverished by injudicious cropping, they 
 are necessary. Commercial fertilizers sometimes fail 
 to give good results because of an excessively acid or 
 alkaline condition of the soil. 
 
 303. Amount of Fertilizer to use per Acre. — When 
 commercial fertilizers are used in general farming, just 
 enough should be applied to produce normal yields. 
 Heavy applications at long intervals are not so pro- 
 ductive of good results as light applications more fre- 
 quently. From 400 to 600 pounds per acre is as much 
 as should be used at one time unless previous trials 
 have shown that heavier applications are necessary. 
 The way in which the fertiHzer is to be applied, as 
 broadcast or otherwise, must be determined by the crop 
 to be grown. The fertilizer should not come in contact 
 with seeds, neither should it be plowed under nor worked 
 into the soil to such a depth that it may be lost by leach- 
 ing before it can be appropriated by the crop. 
 
 304. Excessive Applications of Fertilizers Injurious. — 
 
 An overabundance of plant food has an injurious effect 
 upon crop growth. Plants take their food from the soil 
 in dilute solutions, and when the solution is concentrated 
 abnormal growth results. Potatoes heavily manured 
 
COMMERCIAL FERTILIZERS AND THEIR USE 253 
 
 with nitrate of soda produce luxuriant vines, but only 
 a few small tubers. When a medium dressing is used 
 along with potash and phosphoric acid, a more balanced 
 growth and better yield result. 
 
 Heavy applications of nitrate of soda produce a rank 
 growth of straw, with a low yield of grain. The excess 
 of nitrogen causes the mineral matter to be utilized for 
 straw and leaves only a small amount for grain produc- 
 tion. When applications of commercial fertilizers are 
 too heavy, plants take up unnecessary amounts of food 
 and fail to make good use of it. In fact, crops may be 
 overfed, or fed an unbalanced ration, the same as ani- 
 mals. Hence in the use of fertilizers excessive and un- 
 balanced applications are to be avoided. 
 
 305. Fertilizing Special Crops. — There are crops 
 
 which need special help in obtaining some one element, 
 
 and in using fertilizers the rule should be to help those 
 
 crops which have the greatest difficulty in obtaining 
 
 food. When the soil does not show a marked defi- 
 
 1 ciency in any one element, light dressings of special 
 
 I purpose manures may be made to the following crops : 
 
 , Wheat. — Nitrogen first, then phosphoric acid. In 
 
 1 the case of some soils, phosphoric acid and potash pro- 
 
 1 duce larger yields than nitrogen. 
 
 j Barley, oats, and rye require manuring like wheat, but 
 I to a less extent. Each crop has a different power of 
 1 assimilating nitrogen. Wheat requires the most help 
 t and barley and rye the least. 
 
254 SOILS AND FERTILIZERS 
 
 Corn. — Phosphoric acid first, then nitrogen and 
 potash. 
 
 Potatoes. — General manuring, reenf orced with pot- 
 ash. 
 
 Mangels. — Nitrogen. 
 
 Tiirnips. — Phosphoric acid. 
 
 Clover. — Lime and potash. 
 
 Timothy. — General manuring. 
 
 306. Commercial Fertilizers and Farm Manures. — 
 
 Commercial fertilizers should not replace farm manures, 
 but simply reenforce them. Although commercial fer- 
 tilizers are called complete manures, they fail to supply 
 organic matter. It is more important in some soils 
 than in others that the organic matter be maintained, 
 because in some soils the organic matter takes a more 
 important part in crop production than does the food 
 applied in commercial forms. When a rich prairie soil 
 is reduced by grain cropping and is allowed to return to 
 pasture, heavier yields of grain are afterward obtained 
 than from similar land which has received only appli- 
 cations of commercial fertilizers. This is due to the 
 action of the humus in the soil. At the Canadian Do- 
 minion Experimental Farms, where comparative trials 
 have been made for eighteen years with farm manures 
 and commercial fertilizers, it has been found that farm 
 manures, even on new lands, give better results than 
 commercial fertilizers for the production of wheat and 
 corn.^^ 
 
CHAPTER XI ■ 
 
 FOOD REQUIREMENTS OF CROPS 
 
 307. Amount of Fertility removed by Crops. — The 
 
 amount of fertility removed from an acre of soil pro- 
 ducing average crops varies between wide limits. For 
 example, an acre of mangels removes 150 pounds of 
 potash, while an acre of flax removes 27 pounds ; an 
 acre of corn removes 75 pounds of nitrogen, while 
 an acre of wheat removes 35 pounds. Crops which 
 remove the most fertility do not always require the most 
 help in obtaining their food. This is because the 
 amount of plant food assimilated is not a measure of 
 the power of crops to obtain food. An acre of corn 
 requires over twice as much nitrogen as an acre of 
 wheat, but wheat often leaves the soil in a more im- 
 poverished condition than corn, because corn has greater 
 power to procure nitrogen and utilize that formed by 
 nitrification after the wheat crop has completed its 
 growth'. The available nitrogen if not utilized by a crop 
 may be lost in various ways. Mangels require twice as 
 much phosphoric acid as flax, but are a strong feeding 
 crop and need less help in obtaining this element. It 
 was formerly beheved the plant food in the matured 
 crop indicated the kind and amount of fertilizing ingredi- 
 ents to apply, and that a correct system of manuring 
 
 255 
 
256 
 
 SOILS AND FERTILIZERS 
 
 required a return to the soil of all elements removed in 
 the crop. Experiments show this view to be incorrect. 
 
 Pounds per Acre of Plant Food removed by Crops ^^ 
 
 Crops 
 
 Gross 
 weight 
 
 Nitro- 
 gen 
 
 Phos- 
 phoric 
 acid 
 
 Potash 
 
 Lime 
 
 Silica 
 
 Total 
 ash 
 
 Wheat, 20 bu. . . 
 
 1200 
 
 25 
 
 12.5 
 
 7 
 
 I 
 
 I 
 
 25 
 
 Straw . . 
 
 
 
 2000 
 
 ID 
 
 35 
 
 7-5 
 20 
 
 28 
 
 35 
 
 7 
 
 115 
 116 
 
 185 
 
 Total . 
 
 
 210 
 
 Barley, 40 bu. 
 
 
 
 1920 
 
 28 
 
 15 
 
 8 
 
 I 
 
 12 
 
 40 
 
 Straw . . 
 
 
 
 3000 
 
 12 
 
 5 
 
 30 
 
 8 
 
 60 
 
 176 
 
 Total . 
 
 
 
 
 40 
 
 20 
 
 38 
 
 9 
 
 72 
 
 216 
 
 Oats, 50 bu. 
 
 
 
 1600 
 
 35 
 
 12 
 
 10 
 
 1-5 
 
 15 
 
 55 
 
 Straw . . 
 
 
 
 3000 
 
 15 
 
 50 
 
 6 
 18 
 
 35 
 
 45 
 
 9-5 
 
 II.O 
 
 60 
 
 150 
 205 
 
 Total . 
 
 75 
 
 Corn, 65 bu. 
 
 
 
 2200 
 
 40 
 
 18 
 
 15 
 
 I 
 
 I 
 
 40 
 
 Stalks . . 
 
 
 
 3000 
 
 35 
 
 75 
 
 2 
 20 
 
 45 
 60 
 
 II 
 12 
 
 89 
 90 
 
 160 
 200 
 
 Total . 
 
 
 Peas, 30 bu. 
 
 
 
 1800 
 
 
 18 
 
 22 
 
 4 
 
 I 
 
 64 
 
 Straw . . 
 
 
 
 3500 
 
 — " 
 
 7 
 
 25 
 
 38 
 60 
 
 71 
 
 75 
 
 9 
 10 
 
 176 
 
 Total . 
 
 
 240 
 
 Mangels, 10 tons . 
 
 20000 
 
 75 
 
 35 
 
 150 
 
 30 
 
 10 
 
 350 
 
 Meadow hay, i ton 
 
 2000 
 
 30 
 
 20 
 
 45 
 
 12 
 
 50 
 
 175 
 
 Clover hay, 2 tons . 
 
 4000 
 
 
 28 
 
 66 
 
 75 
 
 15 
 
 250 
 
 Potatoes, 150 bu. . 
 
 9000 
 
 40 
 
 20 
 
 75 
 
 25 
 
 4 
 
 125 
 
 Flax, 15 bu. . . . 
 
 900 
 
 39 
 
 15 
 
 8 
 
 3 
 
 0.5 
 
 34 
 
 Straw 
 
 1800 
 
 15 
 
 3 
 
 19 
 
 13 
 
 3 
 
 53 
 
 Total . . . 
 
 
 
 54 
 
 18 
 
 27 
 
 16 
 
 3-5 
 
 87 
 
FOOD REQUIREMENTS OF CROPS 257 
 
 For example, an acre of wheat contains 35 pounds of 
 nitrogen, while an acre of clover contains 70 pounds ; 
 if 70 pounds of nitrogen were applied to an acre of 
 clover and 35 pounds to an acre of wheat, poor results 
 would follow, because clover can obtain its own nitrogen 
 while wheat is less able to do so, and the 35 pounds 
 would not necessarily come in contact with the roots 
 so that all could be assimilated. While the amount of 
 plant food removed in crops cannot serve as the basis 
 for their manuring, valuable results are obtained from a 
 study of the different elements of fertihty which they 
 contain. In making use of the preceding table, other 
 factors, as the influence of the crop upon the soil and 
 the power of the crop to obtain its food, must also be 
 considered. 
 
 308. Plants exert a Solvent Power in Obtaining 
 
 Food. — It is believed that crops procure some of their 
 
 food from minerals insoluble in water. Experiments 
 
 j by Liebig demonstrate that plants have the power of 
 
 I rendering a portion of their food soluble, provided it 
 
 ; does not exist in forms too inert to undergo chemical 
 
 change. Liebig grew barley in boxes so constructed 
 
 j that all of the water-soluble plant food could be secured. 
 
 I Two of the boxes were manured and two left unmanured. 
 
 In one box which received manure and one which 
 
 I received none, barley was grown. One each of the 
 
 I manured and unmanured boxes was left barren. He 
 
 I collected all of the drain waters and determined the 
 
258 SOILS AND FERTILIZERS 
 
 soluble mineral matter present, also weighed and analyzed 
 the plants. His results showed that 92 per cent of the 
 potash was obtained from forms insoluble in waterJ^ 
 
 The soluble plant food from a fertile soil is not gen- 
 erally sufficient for plant growth,^^ When oats, wheat, 
 and barley were seeded in prepared sand and watered 
 with the teachings from a pot of fertile soil, they made 
 only a limited growth. Oats grown in prepared sand 
 and watered with soil teachings assimilated only 25 per 
 cent as much phosphoric acid as plants grown in fertile 
 soil. See Section 224. The character and concentra- 
 tion of the soil solution are, however, important factors 
 in crop production and some soils may contain sufficient 
 amounts of water-soluble elements to produce crops. The 
 relative amounts of food which plants take from the 
 soil solution and that which they render soluble have 
 not been extensively investigated. 
 
 In the roots of plants there are various organic acids 
 and salts. Between the root and the soil is a layer of 
 water. The plant sap and the soil water are separated 
 by plant tissue, which serves as a membrane. All of the 
 conditions are favorable for osmosis. The sap from the 
 roots finds its way into the soil in exchange for some of 
 the soil water. The acid and other compounds, excreted 
 by the roots, act upon the mineral matter, rendering 
 portions of it soluble, and then it is taken up by the 
 plant. Different plants contain different kinds and 
 amounts of solvents, as well as present different areas of 
 root surface to act upon the soil, and the result is that 
 
FOOD REQUIREMENTS OF CROPS 259 
 
 agricultural crops have different powers of assimilating 
 food. This action of living plant roots upon soils is a 
 digestion process which is somewhat akin to the diges- 
 tion of food by animals. 
 
 Plants not only possess the power of rendering a por- 
 tion of their food soluble, but they are also able to select, 
 and to reject that which is unnecessary. For example, 
 wheat grown on prairie soil with soda in equally abun- 
 dant and soluble forms as the potash will contain 
 relatively little soda compared with the potash ; also 
 many seaweeds contain more potash than soda, although 
 the sea water in which they grow has an excess of 
 sodium salts. 
 
 For the feeding of crops, a nutritive soil solution is 
 desirable, and the soil should have a good stock of 
 reserve material that can be utilized either by action of 
 the plant roots or readily pass into solution in the soil 
 water. 
 
 CEREAL CROPS 
 
 309. General Food Requirements. — Cereal crops con- 
 tain a high per cent of silica and evidently possess the 
 power of feeding upon some of the simpler silicates of 
 the soil,'''* liberating the base elements and using them as 
 food, while the silica is deposited in the outer surface of 
 the straw. As previously stated, cereal crops, although 
 they do not remove large amounts of total nitrogen from 
 the soil, require special help in obtaining this element. 
 There is, however, a great difference among the cereals as 
 
260 SOILS AND FERTILIZERS 
 
 to power of assimilating nitrogen. Next to nitrogen they 
 stand most in need of phosphoric acid. There exists in 
 many soils a greater deficiency of available phosphoric 
 acid and potash than of nitrogen, although, in general, 
 cereal crops are better able to procure these elements 
 than they are nitrogen. The humic phosphates are 
 utilized by nearly all the cereals. 
 
 310. Wheat. — This crop is more exacting in its food 
 requirements than barley, oats, or rye. It is compara- 
 tively a weak feeding crop, and the soil should be in a 
 higher state of fertihty than for other grains. The ex- 
 tensive experiments of Lawes and Gilbert give valuable 
 information regarding the effects of manures on wheat. 
 Their results are given in the following table '.'^ 
 
 Average Yield of Wheat per Acre 
 
 
 
 Bushels 
 
 No manure for 40 years 
 
 14 
 
 i5i 
 
 231 
 
 321 
 
 36i 
 32i 
 
 Minerals alone for 32 years 
 
 Nitrogen alone for 32 years 
 
 Farmyard manure for 32 years 
 
 Minerals and nitrogen for 32 years ^ 
 
 Minerals and nitrogen for 32 years ^ 
 
 ^86 pounds of nitrogen as sodium nitrate. 
 *86 pounds of nitrogen as ammonium salts. 
 
 The food requirements of wheat are such that it should 
 be given a favored position in the rotation. It may follow 
 clover, provided the clover sod is light and is fall plowed. 
 
FOOD REQUIREMENTS OF CROPS 26l 
 
 On some soils, however, wheat does not thrive following 
 a sod crop, as it takes nearly a year for a heavy sod 
 residue to get into suitable food forms for a wheat crop, 
 and under such a condition, oats should first be sown, 
 then wheat may follow. On average soil, a medium 
 clover sod, plowed late in summer or in early fall, and 
 followed by surface cultivation, leaves the land in good 
 condition for spring wheat. It is not advisable to have 
 wheat follow barley, because the soil will be too porous, 
 and barley being a stronger feeding crop leaves the land 
 in a poor state as to available plant food. When corn 
 has been well manured, wheat may follow. The food re- 
 quirements of wheat are best satisfied following a light, 
 well-cultivated clover sod, or following oats, which have 
 been grown on heavy sod, or following corn that has 
 been well manured. When wheat is judiciously grown 
 in a rotation and farm manures are used, it is not an ex- 
 hausting crop. Light dressings of farm manure may 
 be used on land that is being prepared for wheat. On 
 many western prairie soils, dressings of phosphate and 
 potash, either alone or in combination, materially increase 
 the yield and improve the quahty of the crop. Potash 
 fertilizers have a tendency to produce strong bright 
 j straw that is more resistant to fungous diseases. Nitro- 
 I gen alone does not give as good results as when com- 
 bined with minerals. 
 
 311. Barley. — While wheat and barley belong to the 
 same general class of cereals, they differ greatly in their 
 
262 SOILS AND FERTILIZERS 
 
 habits and food requirements. Barley is a stronger 
 feeding crop, has greater root development near the 
 surface, and can utilize food in cruder forms. In many 
 of the western states, soils which produce poor wheat 
 crops, from too long cultivation, give excellent yields of 
 barley. This is due to changed conditions, of both the 
 chemical and mechanical composition of the soil. Long 
 cultivation has made the soil porous, and reduced the 
 nitrogen content. Barley thrives best on a rather open 
 soil, and has greater nitrogen assimilative power than 
 wheat. Barley, however, responds liberally to manur- 
 ing, particularly to nitrogenous manures. The experi- 
 ments of Lawes and Gilbert on the growth of barley are 
 briefly summarized in the following table : "^^ 
 
 Average Yield of Barley per Acre for 34 Years 
 
 No manure 
 
 Superphosphate alone 
 
 Mixed minerals 
 
 Nitrogen alone 
 
 Nitrogen and superphosphate 
 
 Farmyard manures 
 
 312. Oats. — Oats can obtain food under more ad- 
 verse conditions than either barley or wheat. They are 
 also less exacting as to the physical condition of the 
 soil. The oat plant will adapt itself to either sandy or 
 clay soil, and will thrive in the presence of alkaline 
 
FOOD REQUIREMENTS OF CROPS 263 
 
 matter or humic acid where wheat would be destroyed. 
 In a rotation, oats usually occupy a position less fa- 
 vored by manures ; they are, however, greatly benefited 
 by fertilizers, particularly those of a nitrogenous 
 nature. The oat crop responds liberally to manuring. 
 Light dressings of farm manure can be applied directly 
 to oat land when well worked into the soil before 
 seeding. 
 
 313. Corn. — Experiments with corn indicate that 
 under ordinary conditions it requires most help in 
 obtaining phosphoric acid. Corn removes a large 
 amount of gross fertility, and if its production is long- 
 continued without the use of manures it impoverishes 
 the soil. Its habits of growth, however, are such that it 
 generally leaves an average prairie soil in better me- 
 chanical condition for succeeding crops. Corn is not 
 injured as are many grain crops by heavy applications 
 of stable manure, and does not, like flax, produce waste 
 products which are destructive to itself. The conditions 
 I are better for wheat culture after one or two corn crops 
 j have been removed from rich, newly broken prairie soil. 
 ! The food requirements of corn are satisfied by applica- 
 1 tions of stable manure, occasionally reenforced with 
 S a little nitrogen and phosphoric acid, and in the case of 
 some soil potash. After clover, corn gives excellent 
 ij returns, and when corn is the chief market crop it 
 , should be favored by having the best position in the 
 ii rotation. 
 
264 SOILS AND FERTILIZERS 
 
 MISCELLANEOUS CROPS 
 
 314. Flax is very exacting in food requirements and 
 for its culture the soil must be in a high state of fertility. 
 It is a type of weak feeding crop. There are but few 
 roots near the surface and consequently it has restricted 
 power of nitrogen assimilation.^^ Flax should be in- 
 directly manured. Direct applications of stable manure 
 produce poor crops, but when the manure is applied to 
 the preceding crop, excellent results are obtained. Flax 
 does not remove a large amount of fertility, but if 
 grown too frequently the tendency is to get the land out 
 of condition, rather than to exhaust it. The best condi- 
 tions for flax culture require that it should be grown on 
 the same land only once in five years. Flax straw does 
 not form suitable manure for flax lands. Dr. Lugger 
 demonstrated that there are produced, when the roots 
 and straw of flax decay, products which are destructive 
 to succeeding flax crops.'^'' Also flax diseases are intro- 
 duced into land by the use of diseased flax seed. The 
 food requirements of flax are met when it follows corn 
 which has been well manured, or a sod which has been 
 given the cultivation described for wheat. Flax and 
 spring wheat are much aHke in food requirements. 
 
 315. Potatoes. — Potatoes are surface feeders, and ] 
 when grown continuously upon the same soil without , 
 manure, the yield per acre decreases more rapidly than i 
 that of any other farm crop. Experiments with pota- I 
 
FOOD REQUIREMENTS OF CROPS 
 
 265 
 
 toes by Lawes and Gilbert, using different manures, 
 gave the following results:'^ 
 
 Average Yield per Acre for 12 Years 
 
 Tons 
 
 CwT. 
 
 No manure 
 
 Superphosphate 
 
 Minerals alone 
 
 Nitrate of soda alone . . . 
 Mixed manures and nitrogen . 
 Farm manures, alternate years 
 
 I 
 
 19I 
 
 3 
 
 5 
 
 3 
 
 71 
 
 2 
 
 41 
 
 5 
 
 171 
 
 4 
 
 3l 
 
 Potatoes require liberal general manuring reenforced 
 with wood ashes or other potash fertilizer. In the rota- 
 tion they should follow grain or pasture, provided the 
 fertility of the soil is kept up. Commercial fertilizers 
 for potato production should contain a fair amount of 
 ! available nitrogen (2 to 3 per cent) and a more liberal 
 i supply of phosphoric acid and potash. See Section 
 
 324- 
 I 
 
 i 316. Sugar Beets. — This crop is more exacting in its 
 j food requirements than any other root crop. Excessive 
 ': fertility is not conducive to a high content of sugar. 
 * Soils in good mechanical condition and medium state 
 of fertility usually give the best results.'^ Sugar beets 
 ! should not receive heavy dressings of stable manure, 
 ' because an abnormal growth results. Nitrogenous fer- 
 tilizers may be applied only in limited amounts, heavier 
 
266 SOILS AND FERTILIZERS 
 
 dressings of potash and phosphoric acid are admissible. 
 When sugar beets follow corn which has been manured, 
 or grain which has left the soil in an average state of 
 fertility, and a medium dressing of commercial fertilizer is 
 applied, the food requirements of the crop are well met. 
 
 317. Roots. — Mangels are gross feeders and re- 
 move a larger amount of fertility from the soil than 
 any other farm crop."* When fed to stock and the 
 manure is returned to the soil, they materially aid in 
 making the plant food more available for dehcate- 
 feeding crops. Mangels are better able to obtain phos- 
 phoric acid than are turnips and need the most help 
 in the way of nitrogen. Turnips are surface feeders 
 with stronger power of nitrogen assimilation than the 
 grains, but with restricted power of phosphate assimi- 
 lation. Manures for turnips should be phosphatic in 
 nature. 
 
 318. Rape is a type of strong feeding plant capa- 
 ble of obtaining its food under conditions adverse to 
 grain crops. When grown too frequently upon the 
 same soil, it does not thrive. On account of its great 
 capacity for obtaining food, it is a valuable crop to 
 use for green manuring purposes.^^ Farm manure is 
 the most valuable fertilizer for rape. 
 
 319. Buckwheat is a strong feeding crop, and its 
 demands for food are easily met. On rich soil, a rank 
 growth of straw results, with poor seed formation. 
 
FOOD REQUIREMENTS OF CROPS 26/ 
 
 Buckwheat is usually sown upon the poorest soil of the 
 farm. Because it is a strong feeder it is frequently 
 used as a manurial crop, being plowed under while 
 green to serve as food for weaker feeding crops. On 
 poor soils a moderate use of mineral fertilizers and a 
 small amount of nitrogen are beneficial. 
 
 * 320. Cotton. — On average soils cotton stands in need 
 first of phosphoric acid and second of nitrogen.^i It is 
 most able to obtain potash. Organic nitrogen as cot- 
 tonseed meal and stable manure appear equally as 
 effective as nitric nitrogen. Phosphoric acid must be 
 applied in the most available forms, although the crop 
 uses but little. The fertihzers should be drilled in at the 
 time of planting. The use of green manuring crops as 
 cowpeas, with an application of marl, gives beneficial re- 
 sults. Marl, which is composed mainly of calcium car- 
 bonate, combines with the acids formed from the decay 
 ' of the vegetable matter and as a result the plant food of 
 the soil is made more available, which is beneficial to 
 1 both soil and crop. There are but few crops which 
 ] respond so readily to fertilizers as cotton. It does 
 ' not remove a large amount of fertility, but when not 
 I systematically grown in a rotation exhausts the soil 
 ] in the same way as when grain is grown continuously. 
 
 321. Hops. — The hop plant is exacting in its food 
 I requirements. An excess of easily soluble plant food is 
 I injurious, while a lack is equally so. An abundance of 
 
268 SOILS AND FERTILIZERS 
 
 food in organic forms is most essential. Heavy dressings 
 of farm manures may be applied. Where hops are 
 grown there is a tendency to use all the manure on 
 the hops, while the rest of the farm is left unma- 
 nured. Very light applications of commercial fertili- 
 zers may be used in connection with stable manure, 
 but such use should be made only after a preliminary 
 trial on a small scale. 
 
 322. Hay and Grass Crops. — Most grass crops have 
 shorter roots than grain crops ; they are surface feeders 
 and not so able to secure mineral food. When a num- 
 ber of crops have been removed, the soil may stand in 
 need of available mineral matter. Farm manures are 
 particularly well adapted for fertilizing grass. Applica- 
 tions of nitrogenous manures result in discouraging the 
 growth of clover. Heavy manuring of grass land has a 
 tendency to reduce the number of species, and one kind 
 is apt to predominate.^^ On some soils ashes, and on 
 others lime fertilizers, have been found very beneficial. 
 The manuring of grass must be varied to meet the needs 
 of different soils. Permanent meadows require different 
 manuring from meadow introduced as an important crop 
 in the rotation. Permanent meadows should receive an 
 annual dressing of farm manure or of a commercial fer- 
 tilizer containing phosphoric acid, potash, and a fair 
 
 amount of nitrogen. ! 
 
 * I 
 
 323. Leguminous Crops. — For leguminous crops | 
 potash and lime fertilizers have been found of special 
 
 «< 
 
FOOD REQUIREMENTS OF CROPS 269 
 
 value. Analyses of clover and peas show large amounts 
 of both potash and lime. In some cases an application of 
 phosphate fertilizer is necessary before a crop of clover 
 can be secured. Farm manure on sandy or heavy clay 
 soils will materially assist in the production of clover. 
 Sometimes clover fails when grown too frequently upon 
 the same soil, not because the soil is exhausted but be- 
 cause of the development in the soil of organic products 
 which are destructive to growth. As the result of grow- 
 ing leguminous crops, the food requirements of which 
 are inexpensive, the soil is enriched with nitrogen, and 
 the phosphoric acid is changed to available forms. 
 
 324. Garden Crops. — For general garden purposes, 
 there should be a liberal supply of plant food. Well- 
 composted farm manure can advantageously be reen- 
 forced with commercial fertilizers. A liberal use of 
 manure insures not only the maximum yield, but crops 
 of the best quality. Maturity of crops also is influenced 
 by fertilizers. 
 
 Voorhees^^ recommends as a fertilizer for general gar- 
 den purposes one containing : 
 
 
 Per Cent 
 
 Nitrogen 
 
 4.00 
 8.00 
 
 Phosphoric acid 
 
 Potash 
 
 10.00 
 
 
 
 This and similar fertilizers can be applied at the rate 
 of 1000 pounds per acre. To meet the requirements 
 
2/0 SOILS AND FERTILIZERS 
 
 of special crops, as spinach and cabbage, an additional 
 dressing of nitrate of soda may be used. Asparagus 
 should preferably be fertilized after harvesting the 
 crop, so as to encourage new growth and the storing 
 up of reserved building material in the roots for next 
 year's growth. 
 
 For early maturing garden crops, a fair but not ex- 
 cessive amount of nitrogen should be applied; also a 
 liberal supply of phosphates will be found advantageous. 
 Some garden crops, as cucumbers, pumpkins, and squash, 
 thrive best when their food is in organic forms, as the 
 humate compounds derived from farm manures. A 
 continuous supply of available plant food is thus fur- 
 nished to the growing crop. Onions are benefited by 
 a generous dressing of soluble nitrogen. Celery also 
 should be well supplied with soluble nitrogen combined 
 with soluble forms of mineral food. Tomatoes require 
 general fertilizing ; for early maturity, nitrogen, as 
 nitrate of soda, is beneficial, but an excess should be 
 avoided ; for late maturity, farm manures and com- 
 mercial fertilizers containing less nitrogen may be 
 used. For general garden purposes, a complete fer- 
 tilizer is preferable to an amendment, as a better bal- 
 anced growth is secured which favorably affects both 
 the yield and the quahty. 
 
 325. Fruit Trees. — In the manuring of fruit trees, 
 the first object is to produce thrifty trees, as subsequent 
 fertilizing for fruit will not give satisfactory results with 
 
FOOD REQUIREMENTS OF CROPS 27I 
 
 poorly grown and partially developed trees. In order 
 to promote growth, a liberal supply of a complete ferti- 
 lizer should be used, and the soil should be kept in the 
 best mechanical condition. When an orchard is in full 
 bearing, there is as heavy a draft upon the soil as when 
 a wheat crop is grown.^ To meet this, farm manures 
 and commercial fertilizers should be used liberally. 
 The productive period of an orchard is materially 
 lengthened by judicious use of fertilizers. The quality 
 of the fruit is often, adversely affected by a scant supply 
 of plant food. A quick acting fertilizer, containing 
 kainit, nitrate of soda, and dissolved phosphate rock, 
 should be used in the spring, followed if necessary by 
 a light dressing of some manure which yields up its 
 fertility more slowly. An excess of nitrogen, however, 
 should be avoided. Stone fruits are benefited by the 
 addition of lime to the fertilizer. Lime fertilizers impart 
 hardiness to fruit trees. 
 
 I 326. Small Fruits. — On account of the comparatively 
 I limited bearing period of small fruits, the land should 
 } be brought to a high state of productiveness and 
 ! good physical condition by liberal use of farm manures 
 (previous to planting. Quick acting fertihzers are the 
 ' most suitable for small fruits. Dressings of nitrate of 
 soda, 50 to 100 pounds per acre, can be applied early in 
 ^the season to promote leaf activity. This should be 
 I followed by an application of a general fertihzer con- 
 taining about 3 per cent of available nitrogen, 8 per 
 
2/2 SOILS AND FERTILIZERS 
 
 cent of phosphoric acid, and lO per cent of potash. 
 The amount used should range from 200 to 400 pounds 
 per acre until the character and needs of the soil are 
 determined. It will often be found that large amounts 
 can be used economically. 
 
 327. Lawns. — In making a lawn, a mixture of six 
 parts of bone ash , two parts of muriate of potash, and 
 one part of nitrate of soda can be applied at the rate of 
 5 to 7 pounds per square rod prior to seeding. A good 
 lawn should have a subsoil that is fairly retentive of 
 moisture, one containing 10 to 15 per cent of clay or'| 
 a large amount of fine silt. Too much potash and; 
 lime encourage exclusive growth of clover and crowd- 
 ing out of grasses. During the season, two or three! 
 applications can be made of a commercial fertilizer 
 containing about 3 per cent of nitrogen, 10 per cent 
 of phosphoric acid, and 3 per cent of potash, at the 
 rate of one pound per square rod. When part of the| 
 nitrogen is in the form of nitrates and part as ammo-t 
 nium salts, better results are secured than when thei 
 nitrogen is all in one form. It is also advisable to) 
 supply the phosphoric acid in more than one form. 
 An even application of fertilizer to a lawn is quite 
 necessary, otherwise the growth is "patchy." Hard 
 wood ashes evenly spread at the rate of i to 2 pounds) 
 per square rod and reenforced with nitrate of soda cacj 
 be used advantageously as a lawn fertilizer. 
 
CHAPTER XII 
 
 ROTATION OF CROPS AND CONSERVATION OF SOIL 
 FERTILITY 
 
 328. Object of Crop Rotation. — The object of system- 
 atic rotation of crops is to conserve the fertihty of the 
 soil and at the same time to produce maximum yields. 
 In order to accomplish this, the food requirements 
 of different crops must be met by good cultivation 
 and judicious manuring. Rotations must be planned 
 according to the nature of the soil and the system of 
 farming that is to be followed. For general grain 
 farming a different rotation is required than for ex- 
 clusive dairying. Whatever the nature of farming, the 
 whole farm should gradually undergo a systematic ro- 
 tation. If the farm is uneven in soil texture, different 
 I rotations may be practiced on the various parts. There 
 jis no way in which soils are more rapidly depleted of 
 I fertility than by the continued culture of one crop. In 
 I exclusive wheat raising, for example, the losses are not 
 'confined to the fertility removed in the crop, but other 
 losses occur as described in the chapter on nitrogen. 
 iWhen wheat is systematically grown in alternation with 
 'other crops, losses of nitrogen are reduced to the mini- 
 imum. 
 
 i T 273 
 
274 SOILS AND FERTILIZERS 
 
 When remunerative crops can no longer be produced, 
 the soil is said to be exhausted. Soil exhaustion may 
 be due either to a lack of plant food, to bacterial 
 products, or to poor physical conditions arising from 
 the soil being temporarily out of condition because of 
 a one-crop system and poor methods of cultivation. 
 
 329. Principles involved in Crop Rotation. — There 
 
 are a few fundamental principles with which all rota- 
 tions should conform. Briefly stated these are : 
 
 1. Deep- and shallow-rooted crops should alternate. 
 
 2. Humus-consuming and humus-producing crops 
 should alternate. 
 
 3. Crops should be rotated so as to make the best 
 use of the preceding crop residue. 
 
 4. Crops should be rotated so as to secure nitrogen 
 indirectly from atmospheric sources and to promote 
 desirable bacterial activities in the soil. 
 
 5. Crops should be rotated so as to keep the soil in 
 the best mechanical condition. 
 
 6. In arid regions, crops should be rotated so as to 
 make the best use of the soil water. 
 
 7. An even distribution of farm labor should be se- 
 cured by a rotation. 
 
 8. Farm manures and fertilizers should be used in 
 the rotation where they will do the most good. 
 
 9. Rotations should be planned so as to produce 
 fodder for stock, and so that every year there will be I 
 some important crop to be sold. | 
 
ROTATION OF CROPS 275 
 
 330. Deep- and Shallow-rooted Crops. — When deep- 
 and shallow-rooted crops alternate, the draft upon the 
 surface soil and subsoil is more evenly distributed and 
 the physical condition of the soil is improved. In many 
 soils, nitrogen and phosphoric acid are more abundant 
 in the surface soil while potash and lime predominate 
 in the subsoil. When such a condition exists the 
 alternating of deep- and shallow-rooted crops is very 
 beneficial, because the surface soil is gradually enriched 
 by accumulations of fertility from the subsoil, deposited 
 by decay of the residue of the deep-rooted crops, 
 
 331. Humus-consuming and Humus-producing Crops. 
 
 — When grain or hoed crops are grown continuously, 
 
 oxidation of the humus occurs, and the chemical and 
 
 physical properties of the soil are entirely changed by 
 
 loss of the humus. The rotating of grass and grain 
 
 crops and the use of stable manure serve to maintain 
 
 the humus equilibrium. On some soils hme may be re- 
 
 , quired along with the humus to prevent the formation 
 
 ( of humic acid, and in such cases the best conditions 
 
 : exist when both lime and humus materials are supplied. 
 
 Alternation of humus-producing and humus-consuming 
 
 I crops is one of the essentials of a rotation. 
 
 I 
 
 I 332. Crop Residues. — Crop residues should always 
 
 be placed at the disposal of weak feeding crops. After 
 
 ' a light clover and timothy sod, wheat or flax should 
 
 j be grown in preference to barley or mangels. The 
 
2/6 SOILS AND FERTILIZERS 
 
 weak feeding crop should be followed by a strong 
 feeding crop, and then each is properly supplied with 
 food. It would be poor economy, on an average 
 soil, to follow clover and timothy with mangels, then 
 with barley, and finally with flax, because the flax 
 would be placed at a serious disadvantage following two 
 strong feeding crops. If reversed, the crops would 
 be placed in order of assimilative power, and the 
 best use would be made of the sod-crop residue. 
 When crops of dissimilar feeding habits follow each 
 other, not only are the crop residues used to the best 
 advantage, but the soil is relieved of excessive demands 
 on special elements. For example, wheat and clover 
 take different amounts of potash and lime from the 
 soil. Wheat has the power of feeding upon silicates 
 of potash which clover cannot assimilate, hence wheat 
 and clover in rotation reheve the soil of excessive 
 demands on the potash. 
 
 333. Nitrogen-consuming and Nitrogen-producing Crops. 
 
 — It is possible in a five-course rotation to maintain or 
 even increase the nitrogen of the soil without the use 
 of nitrogenous manures. In Section 145 an example 
 is given of a rotation which has left the soil with a 
 better supply of nitrogen than at the beginning. 
 When a soil produces a good clover crop once in 
 five years, and stable manure is used once during 
 that time, the soil nitrogen is not decreased. Not only 
 is nitrification influenced by cultivation and crop rota- 
 
ROTATION OF CROPS 2// 
 
 tion, but other bacterial changes are also affected. The 
 entire bacterial flora of a soil may be changed by 
 modifications of systems of cultivation, cropping, and 
 manuring. By means of rotating nitrogen-producing 
 and nitrogen -consuming crops, grain can be sold from 
 the farm without purchasing nitrogenous manures. 
 Conservation of the nitrogen and humus of the soil 
 is one of the most important points to consider in the 
 rotation of crops. 
 
 334. Influence of Rotation upon the Mechanical Con- 
 dition of Soils. — With different kinds of crops the 
 mechanical condition of soils is constantly undergoing 
 change. Grain crops and hoed crops tend to make 
 the soil open in texture. Grass crops have the opposite 
 effect. All soils should undergo periodic compacting 
 and loosening. Some require more of one treatment 
 than of the other. In a rotation the action of the 
 crop upon the mechanical condition of the soil should 
 be considered, otherwise the soil may get into poor 
 condition to retain water or become so loose that heavy 
 losses occur through wind storms. Sandy soils are 
 improved by methods of cropping which compact the 
 soil, while heavy clays require the opposite treatment. 
 The rotation should be made to conform to the re- 
 quirement of the soil. 
 
 335. Economic Use of Soil Water. — The rotation 
 should not be of such a nature as to make excessive 
 
278 SOILS AND FERTILIZERS 
 
 demands upon the soil water. For example, after a 
 grain crop has been produced, it is best in regions of 
 scant rainfall to plow the land and get it into condi- 
 tion to conserve the water for the next year's crop, 
 rather than to attempt to raise a catch crop the same 
 year. During years of heavy rainfall catch crops may 
 be grown for green manure to increase the humus con- 
 tent of the soil. Crops removing excessive amounts 
 of water should not be grown too frequently. Sun- 
 flowers, for example, remove twenty times more water 
 than grain crops, and cabbage removes more water 
 than many other crops. With a good rotation and 
 systematic cultivation a water balance may be carried 
 in the soil from one year to the next, so that crops 
 will be supplied in times of drought. 
 
 336. Rotation and Farm Labor. — The rotation of 
 crops should be so planned that there is an even 
 distribution of farm labor. The importance of this is 
 so plain that its discussion seems unnecessary. It 
 is one of the most important points to consider in 
 economic farming, and should not be lost sight of in 
 planning rotations. 
 
 337. Economic Use of Manures. — Farm manure 
 should be applied to those crops which experience has 
 shown to be the most benefited by its use. At least 
 once during a five years' rotation the land should 
 receive a dressing of stable or some other manure. 
 
ROTATION OF CROPS 
 
 279 
 
 When commercial fertilizers are used,, they should be 
 applied to the crops which need the most help in 
 obtaining food. With the growing of clover and the 
 use of farm manures, the minimum amount of com- 
 
 FlG. 46. A W'heat Field. This crop was grown on land where farm manure 
 was used and a rotation of crops practiced. Ayer, Photographer. 
 
 mercial fertilizer is required for general crop production. 
 It is more economical to reenforce the farm manures 
 with fertilizers especially adapted to the soil and crop 
 than to purchase complete fertilizers for all crops. 
 
 338. Salable Crops. — In all farming, something must 
 be sold from the farm. It should be the aim to sell 
 
280 SOILS AND FERTILIZERS 
 
 products which remove the least fertility, or if those 
 are sold which remove large amounts, to return in 
 cheaper forms the fertility sold. In a good rotation 
 it is the plan to have at least one salable crop each 
 year. The whole farm need not undergo the same 
 rotation at the same time, and the rotation may be 
 subject to minor changes, as circumstances require. 
 To illustrate, wheat and flax occupy about the same 
 position in a rotation. If at seeding time the indica- 
 tions are that wheat will be a poor paying crop and 
 flax command a high price, flax should be sown. The 
 rotation should be such that one of two or three crops 
 may be grown as circumstances require. A rotation 
 should be reasonably flexible. 
 
 339. Rotation Advantageous in Other Ways. — A good 
 rotation will be found advantageous in other ways than 
 those mentioned. With one line of cropping, land be- 
 comes foul with weeds and insects which do not thrive 
 when crops are rotated. Frequently the rotation must be 
 planned so as to reclaim the land from weeds and rav- 
 ages caused by insect pests. Many insects are capable 
 of living only on a special crop ; when this crop is grown 
 continuously on the same land the best conditions for in- 
 sect ravages exist, and relief is secured only by rotation 
 of crops. Fungous diseases also are most liable to occur 
 on soils which produce annually the same crop, as the 
 conditions are favorable for the propagation and hiber- 
 nating of the disease-producing spores. 
 
ROTATION OF CROPS 28 1 
 
 340. Long- and Short-course Rotations. — Rotations 
 vary in length from 2 to 17 years. Long-course rota- 
 tions are more generally followed in European and 
 other of the older countries. The length of the rotation 
 can be determined only by the conditions existing in 
 different localities. As a general rule, long-course rota- 
 tions should be attempted mainly on large farms and after 
 a careful study of all of the conditions relating to the 
 system of farming that it is desired to follow. For north- 
 ern latitudes a rotation of four or five years gives excel- 
 lent results. In some localities three-course rotations 
 are the most desirable. 
 
 A rotation that is suitable for one locality or kind of 
 farming may be unsuitable for other localities and con- 
 ditions. Because of variations in soil, climate, and rain- 
 fall, no definite standard rotation can be proposed that 
 will be applicable to all cases. 
 
 341. Example of Rotation. — In deahng with the sub- 
 ject of rotations it is best to take actual problems as 
 they present themselves and plan rotations that will 
 best meet all of the conditions. For example, a farm 
 of 160 acres is to be rotated with the main object of 
 producing fodder for five stock, and a small amount of 
 grain for sale. To meet these requirements the rotation 
 outUned on pages 282 and 283 is suggested. ^^ 
 
 The farm is divided into eight fields of 20 acres each; 
 seven fields are brought under the rotation, while one 
 field is left free for miscellaneous purposes. Each year 
 
282 
 
 SOILS AND FERTILIZERS 
 
ROTATION OF CROPS 
 
 283 
 
 
 
 
 
 
 
 
 
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284 SOILS AND FERTILIZERS 
 
 there are produced 20 acres of corn, 20 acres of timothy 
 and clover hay, 10 acres each of wheat and flax, 20 acres 
 of barley, and 5 acres each of corn fodder, rye, peas, 
 and potatoes, while 20 acres are reserved for pasture. 
 The main income is derived from the sale of live stock 
 and dairy products. 
 
 Problems on Rotation 
 
 1. Plan a rotation for general farming (160 acres), using the 
 following crops : clover, timothy, barley, oats, potatoes, and corn. 
 The soil is in an average state of fertility. Twenty-five head of 
 stock are kept. 
 
 2. Plan a three-course rotation for a sandy soil, the main object 
 being potato culture. 
 
 3. Plan a seven-year rotation for grain farming, using manure 
 and a commercial fertilizer once during the rotation. The soil is 
 a clay loam in a good state of fertility. 
 
 4. Plan a rotation for general farming on a sandy loam. 
 
 5. How would you proceed to bring an old grain farm from a 
 low to a high state of productiveness ? Begin with the feeding of 
 the stock. 
 
 6. Using commercial and special purpose manures, how would 
 you proceed to raise wheat, potatoes, and hay in a suitable rotation 
 and continuously? 
 
 7. Plan a rotation for a northern latitude, where corn cannot be 
 grown, except for fodder, and where clover and timothy fail to 
 do well; wheat and all small grains thrive, also millet, bromuS' 
 inermis, rape, and some of the root crops. The soil is a clay loam, 
 resting on a marl subsoil. Manure is very slow in decomposing. 
 The rotation should be suited to general farming, wheat or flax 
 being the important market crop. , 
 
 8. Plan for a southern farm a rotation in which cotton forms an 
 important part. 
 
CONSERVATION OF FERTILITY 285 
 
 9. Plan a rotation for a market milk farm of 90 acres. One hun- 
 dred head of stock are kept and mostly mill feed purchased. 
 Soiling crops are to be provided ; corn silage and clover are the 
 main coarse fodders. 
 
 CONSERVATION OF FERTILITY 
 
 342. Manures Necessary for Conservation of Fertility. 
 
 — In order to conserve the fertility of the soil, not only 
 must a systematic rotation be practiced, but a proper 
 use must be made of the crops produced. When crops 
 are sold from the farm and no restoration is made, soils 
 are gradually depleted of their fertility. No soil has 
 ever been found that will continue to produce crops 
 without the use of manures. Many prairie soils give 
 large yields for long periods without manuring, but 
 they are never able to compete in productiveness with 
 similar soils that have been systematically cropped and 
 manured. With a fertile soil the decline in fertihty is 
 so gradual that it is not observed unless careful records 
 are kept of the yields from year to year. 
 
 j 
 
 j 343. Use of Crops. — The use made of crops whether 
 
 las food for stock or sold directly from the farm de- 
 termines the future crop-producing power of the soil. 
 jWith different systems of farming different uses are 
 |made of crops. When exclusive grain farming is fol- 
 liowed there is no restoration of fertility, while in the 
 Ipase of stock farming, the manure produced contains 
 Jiertility in proportion to the food consumed. If good 
 
286 SOILS AND FERTILIZERS 
 
 care is taken of the manure, and in place of the grains 
 sold mill products are purchased and fed, there is no 
 loss but often a gain of fertility. Between these two 
 extremes, exclusive grain farming and stock farming, 
 many different systems are practiced which remove 
 from the soil various amounts of fertility. 
 
 344. Two Systems of Farming Compared. — Losses 
 of fertihty from farms are determined by the products 
 sold, the care of the manure, and the fertility in the 
 materials purchased and used on the farm. If an ac- 
 count were kept of the income and outgo of the fertility 
 it would be found that with some systems the soil 
 is gaining, while with others a rapid decline is occur- ' 
 ring. In studying the income and outgo of fertility, it 
 is necessary to calculate the amounts of the three prin- 
 cipal elements, nitrogen, phosphoric acid, and potash in 
 the crops and other products sold. For making these I 
 calculations, tables are given in Sections 185 and 307. 
 In the handling of manure it is impossible to prevent 
 losses, but it is possible to reduce them to very small 
 amounts. Hence in the calculations, a loss of 3 per 
 cent is allowed for mechanical waste and for uneven 
 distribution of the manure ; that is, in addition to the , 
 fertility sold from the farm a mechanical loss of 3 per 
 cent is allowed for all crops raised and consumed as 
 food by stock. 
 
 On one farm the crops raised and sold are : flax 40 
 acres, wheat 50 acres, oats 20 acres, barley 50 acres. 
 
CONSERVATION OF FERTILITY 
 
 287 
 
 No stock is kept, the straw is burned, and the ashes 
 are wasted. In addition to the nitrogen removed in 
 the crops other losses must be considered. Experiments 
 show that when exclusive grain farming is practiced, 
 for every pound of nitrogen removed in the crop, 4 
 pounds are lost from the soil in other ways. This would 
 make the total loss of nitrogen over 28,500 pounds, 
 or 177 pounds per acre, which large as it may seem 
 is the actual loss from the soil when grain only is raised 
 and it is sold. Experiments at the Minnesota Experi- 
 ment Station with a soil that had been cultivated 40 
 years, showed the annual loss per acre of nitrogen in 
 exclusive wheat raising to be 25 pounds through the 
 crop and 146 pounds due to oxidation of the nitroge- 
 nous humus of the soil.^ 
 
 Exclusive Grain Farming 
 Sold from the Farm 
 
 Potash 
 Pounds 
 
 Flax, 40 acres . 
 Flax straw . 
 Wheat, 50 acres 
 Wheat straw 
 Oats, 20 acres . 
 Oat straw 
 Barley, 50 acres 
 Barley straw 
 Total . . 
 
 Nitrogen 
 Pounds 
 
 Phosphoric 
 
 Acid 
 
 Pounds 
 
 1600 
 
 600 
 
 600 
 
 120 
 
 1250 
 
 625 
 
 500 
 
 375 
 
 700 
 
 240 
 
 300 
 
 120 
 
 1400 
 600 
 
 750 
 250 
 
 6950 
 
 3080 
 
 800 
 
 320 
 
 350 
 
 1400 
 200 
 700 
 400 
 
 1500 
 
 5670 
 
 When exclusive grain farming was followed, the annual 
 losses of fertility from this farm of 160 acres were 28,5(X> 
 
288 
 
 SOILS AND FERTILIZERS 
 
 pounds of nitrogen, 3000 pounds of phosphoric acid, 
 and 5500 pounds of potash. 
 
 On a similar farm of 160 acres the crops are rotated 
 as described in Section 341. The amounts of fertility 
 in the crops raised and consumed as fodder, in the 
 products sold, and in the food and fuel purchased, are 
 given in the following table : 
 
 Stock Farming 
 Sold from the Farm 
 
 Butter, 5000 pounds . . . 
 Young cattle, 10 head . . 
 Hogs, 20 of 250 pounds each 
 
 Steers, 2 
 
 Wheat, 10 acres .... 
 
 Flax, 10 acres 
 
 Rye, ID acres 
 
 Total 
 
 Nitrogen 
 Pounds 
 
 5 
 
 200 
 
 100 
 
 48 
 
 250 
 
 390 
 285 
 
 1278 
 
 Phosphoric 
 
 Acid 
 
 Pounds 
 
 5 
 190 
 40 
 38 
 125 
 150 
 128 
 676 
 
 Potash 
 Pounds 
 
 5 
 
 16 
 10 
 
 4 
 
 70 
 
 190 
 
 ll 
 380 
 
 Raised and Consumed on the Farm 
 
 Clover, 20 tons 
 
 Timothy, 20 tons 
 
 Corn, 20 acres 
 
 Corn fodder, i acre 
 
 Mangels, 2 acres 
 
 Potatoes, I acre 
 
 Straw, 40 tons 
 
 Peas, 5 acres 
 
 Oats, 20 acres 
 
 Barley, 20 acres with straw . . 
 
 Total 
 
 Mechanical loss of food consumed, 
 3 per cent 
 
CONSERVATION OF FERTILITY 
 
 289 
 
 Food and Fuel Purchased 
 
 Bran, 5 tons 
 
 Shorts, 5 tons 
 
 Oil meal, i ton 
 
 Hard wood ashes 
 
 Total 
 
 Mechanical loss of material pur- 
 chased, 3 per cent 
 
 Sold from farm 
 
 Loss of food consumed, etc. . . 
 Total 
 
 Food and fuel purchased . . . 
 Balance lost from farm . . . . 
 
 Nitrogen 
 Pounds 
 
 275 
 250 
 100 
 
 625 
 
 19 
 
 1278 
 
 128 
 
 1425 
 
 625 
 800 
 
 Phosphoric 
 
 Acid 
 
 Pounds 
 
 260 
 
 150 
 
 35 
 
 470 
 
 14 
 676 
 
 743 
 
 470 
 273 
 
 Potash 
 Pounds 
 
 150 
 100 
 
 25 
 100 
 
 375 
 
 10 
 380 
 144 
 534 
 
 375 
 159 
 
 The manure produced and used on this farm results 
 in larger crop yields than is the case with exclusive grain 
 culture. The nitrogen gained by the clover and peas 
 more than balances the loss of nitrogen in other crops. 
 Experiments show that a rotation similar to this caused 
 an increase in soil nitrogen. ^^ Manure, meadow, and 
 pasture all tend to increase the soil's humus and ni- 
 trogen. The losses of phosphoric acid and potash 
 are very small, averaging about a pound per acre of 
 each. The manure on this farm is continually bringing 
 into activity the inert plant food of the soil so that 
 every year there is a larger amount of more active 
 plant food, which results in producing larger yields 
 per acre. 
 
290 SOILS AND FERTILIZERS 
 
 The method of farming has a marked effect upon 
 crop yields. The average yield of wheat in those 
 counties in Minnesota where live stock is kept and 
 crops are rotated, is over 10 bushels per acre greater 
 than in similar counties where exclusive grain farming 
 is followed. 
 
 Problems 
 
 Calculate the income and outgo of fertility from the following 
 farms : 
 
 1. Sold from the farm: wheat 40 acres, oats 40 acres, barley 40 
 acres, rye 20 acres, flax 10 acres. The straw is burned and no 
 manures are used. 
 
 2. Sold from the farm : wheat 20 acres, barley 20 acres, flax 5 
 acres, 1000 pounds of butter, 10 hogs, and 10 steers. Purchased : 
 bran 3 tons, shorts 2 tons, oil meal i ton. Crops produced and fed 
 on farm : clover and timothy hay 40 tons, corn fodder 3 acres, 
 corn 10 acres, oats and peas 10 acres, roots i aae, millet i acre, 
 and barley 5 acres. 
 
 3. Sold from the farm : wheat 10 acres, sugar beets 5 acres, milk 
 100,000 pounds, butter 500 pounds, 20 pigs, 6 head of young stock, 
 2 acres of potatoes. Purchased : 5 tons of bran, 2 tons of oil meal, 
 I ton of cottonseed meal, 15 cords of wood, i ton of acid phosphate, 
 1000 pounds of potassium sulphate, and 500 pounds of sodium |j 
 nitrate. Raised and consumed on the farm : corn fodder 15 acres, 
 mangels i acre, peas and oats 5 acres, clover 20 tons, timothy 10 
 tons, straw from grain sold, oats 10 acres, corn 20 acres. 
 
 4. Calculate the income and outgo of fertility from your owa 
 farm. 
 
CHAPTER XIII 
 PREPARATION OF SOILS FOR CROPS 
 
 345. Importance of Good Physical Condition of Seed 
 Bed. — But few soils are in suitable condition for seed- 
 ing without further preparation than simply plowing the 
 land. If the plowing is poorly done, a good seed bed 
 cannot be made. The depth of plowing is of prime 
 importance and is determined largely by the ■ kind of 
 soil, as sand, clay, or loam. (See Section 35.) The 
 condition of the seed bed is influenced not only by the 
 depth of plowing but by its nature as the way in which 
 the furrow slice is left. The treatment after plowing, as 
 disking, harrowing, cultivating, and light rolling, must be 
 determined largely by the character of the soil. Too 
 frequently the preparation of the soil is not given suf- 
 
 I ficient attention and the crop suffers because of a poorly 
 prepared seed bed. Low yields are more generally due 
 
 1 to poor physical condition of the soil than to any other 
 
 I factor. Without the requisite cultivation the natural 
 fertility is not used to the best advantage. 
 
 i 
 
 346. Influence of Methods of Plowing upon the Condition 
 
 ] of the Seed Bed. — ■ A poor seed bed is sometimes due to 
 , complete inversion of the furrow slice and the soil not 
 I being sufficiently pulverized. If a heavy sod has simply 
 I • 291 
 
292 
 
 SOILS AND FERTILIZERS 
 
 been inverted, subsequent harrowing and cultivation fail 
 to pulverize and loosen the tough sod in the lower part 
 of the furrow slice. A good seed bed cannot be made 
 upon such a foundation. When the land is plowed so 
 the furrow slice is left at an angle of 30° to 45°, the sur- 
 
 FlG. 47. Complete Inversion of the Furrow Slice (after Roberts). A poor way 
 of plowing sod land. 
 
 face is corrugated and all vegetation is buried in loose 
 soil. When land that has been plowed in this way is 
 cultivated and harrowed, a better seed bed is formed 
 than is possible on a completely inverted furrow slice. 
 
 The plowing should thoroughly pulverize the soil, 
 completely bury all surface vegetation, and leave the 
 land in a corrugated condition with the furrow slice at 
 
PREPARATION OF SOILS FOR CROPS 
 
 293 
 
 an angle but firmly connected with the subsoil. There 
 should be as thorough disintegration of the soil as pos- 
 sible, and this can best be accomplished by the use of 
 a plow with a bold rather than too flat a moldboard. 
 
 
 
 •^-v^ 
 
 Fig 48. The Furrows standing nearly edgewise (after Roberts). A good 
 way to leave tail plowed land to undergo weathering during the winter, to 
 be followed by thorough cultivation in the spring. 
 
 Roberts states that only about 10 per cent of the energy 
 required for plowing is used by the friction of the mold- 
 board : "about 35 per cent of the power necessary to 
 plow is used by the friction due to the weight of the 
 plow, and 55 per cent by severing the furrow slice and 
 the friction of the land slide." Hence in the prepara- 
 tion of the seed bed, it is economy to secure as much 
 pulverization of the soil by the action of the plow as 
 possible rather than to leave too much for subsequent 
 treatment. The plow is the most economical implement 
 for pulverizing the land. 
 
294 
 
 SOILS AND FERTILIZERS 
 
 347. Influence of Moisture Content of the Soil at the 
 Time of Plowing. — The condition of the soil, particu- 
 larly its moisture content, at the time of plowing, has 
 much to do with the formation of a good seed bed. If 
 soils are too dry when plowed, they fail to pulverize, and 
 
 
 Fig. 49. Ideal Plowing (after Roberts) . The land left in a formed, pulverized 
 condition and all the sods turned under. 
 
 then disking, harrowing, and in some cases light rolling, 
 which make additional expense, must be resorted to 
 in order to produce a fine, mediumly compact, and well- 
 pulverized seed bed. If clay soils are plowed when too 
 wet, the pores of the subsoil become clogged, a condi- 
 tion known as puddling takes place, and the furrow 
 slice dries and forms hard lumps and clods. The con- 
 dition in which the soil is left after plowing, particularly 
 in the case of clay soils, has much to do with the char- i 
 acter of the seed bed and the subsequent yield of the 
 crop. At the Oklahoma Station, winter wheat land 
 plowed in July was moist and mellow, while that plowed 
 
 
PREPARATION OF SOILS FOR CROPS 295 
 
 in September was dry and lumpy ; the early plowed 
 mellow land gave a yield of 31.3 bushels per acre and 
 the late plowed lumpy land produced only 13.3 bushels. 
 
 348. Influence upon the Seed Bed of Pulverizing and 
 Fining the Soil. — If the land is lumpy and the lower 
 stratum of the seed bed is not pulverized and firmed, the 
 soil water is readily lost by percolation, evaporation takes 
 place rapidly, and the crops are poorly fed because the 
 roots are unable to penetrate the hard lumps and secure 
 plant food. If a soil is inclined to be lumpy, the cul- 
 tivation, including the plowing, should be carried on 
 largely with the view of thorough pulverization. When 
 a seed bed is well prepared, the soil warms up more 
 readily ; the loosening and pulverizing enable the 
 heat of the sun's rays to more readily penetrate the 
 soil and bring it into good condition for promoting 
 growth. 
 
 349. Aeration of Seed Bed Necessary. — Crop roots 
 require air for functional purposes. In sand and loam 
 the air spaces make up half or more of the total 
 volume. It is not necessary to cultivate such soil with 
 the view of increasing the air spaces, but with compact 
 soils, as heavy clays, plowing should result in aeration 
 of the soil and an increase in the number of air spaces, 
 as the air of the soil takes an important part in render- 
 ing plant food available. (See Section 59.) If soils are 
 plowed when too wet, they are not sufficiently aerated. 
 
296 SOILS AND FERTILIZERS 
 
 The amount and kind of cultivation to secure the venti- 
 lation or aeration necessary for crop production must 
 be regulated according to the character of the soil, as 
 sand, clay, or loam, and the climatic conditions. The 
 cultivation which is given soils for moisture conserva- 
 tion also secures the proper aeration. 
 
 In discussing the importance of a mellow seed bed, 
 King says ; ^^ " When a mellow, open seed bed has been 
 prepared, and its temperature has been raised to the 
 proper point, should a rain fall upon it, that water will 
 tend to pass through its wide pores quickly to the 
 deeper soil, and without leaching it as badly as would 
 be the case were the soil more compact ; so that in 
 the early season when there is an overabundance of 
 moisture, it is best, for warmth, for aeration, and to 
 lessen loss of fertility by percolation, to have a mellow 
 seed bed." 
 
 350. Preparation of Seed Bed without Plowing. — 
 
 Loam soils which have been subjected to a systematic 
 rotation of crops ending with corn, need not be plowed, 
 but the seed bed for the succeeding grain crop can 
 be prepared simply by disking the corn land. Surface 
 tillage of the corn crop has sufficiently loosened and 
 aerated the soil and has caused an accumulation of 1 
 available plant food near the surface which would be 
 buried and be less available to the crop if the land were 
 plowed too deeply. On heavy clay lands this method 
 of preparing the seed bed is not advisable ; but on the J 
 
PREPARATION OF SOILS FOR CROPS 29/ 
 
 silt soils of the Northwest it has given excellent results 
 and is beneficial in promoting crop growth. 
 
 351. Mixing of Subsoil with Seed Bed. — Some soils 
 are improved by deep plowing and mixing the surface 
 and subsoils to form the seed bed. Such soils are 
 usually acid in character and contain a large amount 
 of organic matter, in which case the mixing of the 
 surface and subsoils improves both the physical and 
 chemical properties. With sandy soils the mixing of 
 the surface soil with the subsoil is not advantageous, as 
 it dilutes the stores of plant food which are greater in 
 the surface soil ; then, too, the physical properties of 
 the soil are not improved. Combining the surface and 
 subsoils in the case of heavy clays should be done 
 gradually and at each period in the rotation after an 
 application of farm manure. In the cultivation of clay 
 soils it should be the aim to secure a deep layer of 
 i thoroughly pulverized, aerated, and fertilized soil. In 
 j the preparation of the seed bed, the character and con- 
 dition of the subsoil is equally as important as of the 
 j surface soil. 
 
 I 352. Cultivation to Destroy Weeds. — One of the chief 
 ( objects of cultivation is to destroy weeds, and for this 
 purpose it should be given early in the year before 
 the weeds become firmly estabhshed. Weeds are most 
 I easily destroyed at the time of germination and before 
 ; the leaves appear above ground. The plow should be 
 
298 SOILS AND FERTILIZERS 
 
 relied upon largely for the destruction of deep-rooted 
 perennial weeds, while the cultivator is effectual for 
 the destruction of annuals. When weeds are plowed 
 under or destroyed by cultivation they serve as a green 
 manurial crop, adding vegetable matter and humus to 
 the soil and thus improving its condition instead of 
 reducing the yield of crops by appropriating fertility, 
 as they do if allowed to grow and mature. Cultivation 
 which secures aeration of the soil and conservation of 
 the soil moisture is also effectual for the destruction 
 of weeds. 
 
 353. Influence of Cultivation upon Bacterial Action. — 
 Cultivation has a marked influence upon bacterial ac- 
 tion. Some of the soil organisms, as the nitrifying 
 organisms (see Section 150), require oxygen for their 
 existence, hence cultivation which increases the sup- 
 ply of oxygen in the soil increases the activity of such 
 organisms. In the absence of air, anaerobic fermenta- 
 tion occurs, and such fermentation is unfavorable to 
 crop growth. When acid peaty soils are aerated bac- 
 terial action is induced which results in more rapid 
 decay and a lowering of the per cent of total organic 
 matter, including the deleterious organic acids. Neu- 
 tralizing the organic acids of soils by applications of 
 lime and wood ashes hastens bacterial action, and during 
 the process of nitrification this is not alone confined 
 to the nitrogenous compounds of the soil, as the nitri- 
 fying organisms require phosphates as food and these 
 
PREPARATION OF SOILS FOR CROPS 299 
 
 are left after nitrification in a more available condition. 
 The mineral as well as the organic matter of the soil 
 is subject to the action of micro-organisms, and the 
 cultivation which the soil receives can be made either 
 to accelerate or to retard this action. Many of the 
 chemical changes which take place in the soil result- 
 ing in the liberation of plant food are induced by aerobic 
 organisms, hence the importance of thorough cultiva- 
 tion to induce bacterial action. Each type of soil has 
 its own characteristic microscopic flora, which can be 
 either favorably or unfavorably influenced by cultivation. 
 
 354. Cultivation for Special Crops. — While the gen- 
 eral principles of cultivation apply to all crops, the ex- 
 tent to which loosening or compacting should be carried 
 must be determined by the character of the soil and the 
 crop that is to be produced. Methods of cultivation 
 must be varied to meet the requirements of different 
 soils and different crops. The physical condition of 
 the soil for general farm crops is discussed in Chapters 
 I and XL For the production of a special crop, the 
 cultivation must be adapted to the specific needs as 
 to manner of growth, kind of food needed, physical 
 condition of the soil, temperature, and moisture. A 
 knowledge of these requirements can be obtained only 
 by experimental methods. The cultivation of a new 
 crop should not be attempted on a large scale without 
 a preHminary study of the crop. The production of 
 sugar beets for the manufacture of sugar, of flax for 
 
300 SOILS AND FERTILIZERS 
 
 fine fiber, or of tobacco under shade requires a high 
 degree of both knowledge and skill. For the pro- 
 duction of special crops the preparation of the seed 
 bed and the subsequent cultivation are matters of prime 
 importance, and should receive careful consideration on 
 the part of the cultivator. Many times agricultural 
 industries undertaken in new countries have failed 
 because the cultivation of the special crop used in the 
 industry has not been successfully accomplished on 
 account of lack of knowledge of the cultural methods 
 necessary. 
 
 355. Cultivation to prevent Washing and Gullying of 
 Lands. — In regions of heavy rainfall, rolling land of 
 clay texture often becomes gullied by the watpr flowing 
 in large amounts over the surface. Under such condi- 
 tions the preparation of a seed bed, and cultivation of 
 the soil so as to prevent washing are often difficult prob- 
 lems. To prevent gullying, the water currents should 
 be divided as much as possible by plowing narrower 
 lands and by increasing the number of shallow dead 
 furrows. The larger drains should be constructed with 
 the view of preventing the formation of deep guUies, and 
 this can in part be accomplished by encouraging the 
 growth of special grasses with fibrous roots which serve 
 as soil binders. Soils which gully are improved by the 
 addition of farm manures and other humus-forming 
 material which bind together the soil particles ; also by 
 seeding and cultivating at right angles to the slope of 
 
PREPARATION OF SOILS FOR CROPS 3OI 
 
 the land so as to break the force of the water. The 
 water should be encouraged to percolate through the 
 soil rather than to flow over the surface. (See Section 
 25.) 
 
 356. Bacterial Diseases of Soils. — Many of the bac- 
 terial diseases to which crops are subject are caused 
 primarily by a diseased condition of the soil. These 
 diseases can often be checked by the right kind of culti- 
 vation, by securing good drainage, and by proper soil 
 ventilation supplemented with the application of alkaline 
 , matter as wood ashes and land plaster. Undrained soils 
 I are unsanitary ; the products of decay of the organic 
 ' matter accumulate in the soil and produce toxic or poi- 
 (sonous compounds which affect crops. When soils are 
 ,1 drained, air is admitted which prevents the formation 
 iof these products. Both bacterial and fungous diseases 
 (of soils may be controlled by cultivation, particularly 
 when it improves the general sanitary condition of the 
 iSoil. With improvement in sanitary condition, there 
 :|is less liability of bacterial diseases becoming established 
 land causing destruction of the crop. As a result of 
 jSome forms of bacterial action, chemical substances in- 
 jjurious to plants are produced, and by controlling bac- 
 iterial action the formation of these is prevented. Some 
 of the organisms propagated in the soil cause bacterial 
 |diseases of dairy and other farm products. The use of 
 isoil disinfectants is possible only where a small area is 
 ijinvolved ; they are not applicable to large tracts as they 
 
302 SOILS AND FERTILIZERS 
 
 destroy the beneficial as well as the injurious soil 
 organisms. A good sanitary condition of the soil is 
 as essential for the production of crops as are suitable 
 hygienic surroundings for the rearing of live stock. 
 Sunlight and air are important factors in bringing about 
 an improved sanitary condition of diseased soils. 
 
 By the rotation of crops many bacterial diseases, as 
 flax wilt and clover sickness, are controlled. Some of 
 these are disseminated by the use of infected seed. 
 By sprinkling the seed grain with a disinfectant as a 
 dilute solution of formalin (i pound of formalin in 50 
 gallons of water) bacterial diseases, as grain smuts, ; 
 are held in check. Low forms of plants, as fungi, 
 also develop in soils when conditions are favorable, \ 
 and take an important part in changing the char-; 
 acter of the soil. Their action may be either beneficial I 
 or injurious, depending upon the condition of the soil 
 There is a very close relationship between soil san- 
 itation, which results in the avoidance of crop diseases, 
 and the quality and yield of agricultural products. 
 
 357. Influence of Crowding Plants in the Seed Bed. — j 
 
 The number of plants which a seed bed should produce 
 is dependent mainly upon the supply of water and plant 
 food. By means of thick or thin seeding, the general 
 character of crops may be influenced within definitei 
 limits. Either an excessive or a scant amount of seedj 
 gives poor results. If overcrowded, plants fail to de- 
 velop normally either for want of plant food or water, or 
 
PREPARATION OF SOILS FOR CROPS 303 
 
 because of poor sanitary conditions, or from lack of 
 room for development. Experiments show that an ex- 
 cessive amount of seed wheat as more than lOO pounds 
 per acre of spring wheat does not give good results. 
 Each crop has its limit beyond which it is not desirable 
 to crowd the plants in the seed bed. When there is 
 crowding, unhygienic conditions prevail and the lack of 
 air, sunhght, and good ventilation encourages bacterial 
 diseases, while on the other hand too few plants favor 
 the growth of weeds and an abnormal development of 
 the crop. In the seeding of grains and other farm crops, 
 the amount of seed to be used per acre should be deter- 
 mined by the quality of the seed and the local conditions, 
 as climate and soil, together with any special character- 
 istic desired in the way of composition and character of 
 
 the crop. 
 
 I 
 
 358. Selection of Crops. — The selection of the most 
 suitable crops to be grown is largely a local problem and 
 must be determined by climatic and soil conditions. The 
 preference of farm crops for certain types of soil is dis- 
 cussed in Sections ii to 17, and it is not advisable to 
 attempt to grow crops upon soils to which they are not 
 naturally adapted or under unfavorable climatic condi- 
 tions. Practical experience is the best guide in re- 
 gard to the selection of crops and the most suitable 
 lines of farming to follow, and it will be found that this 
 experience is in harmony with the laws governing the 
 conservation and development of the fertility of the soil. 
 
304 SOILS AND FERTILIZERS 
 
 Temporary methods of farming, as exclusive grain raising, 
 can be foilowed for a short time on new soils ; but it is 
 desirable that each type of soil should be subjected to a 
 judicious system of cultivation, fertilizing, and cropping 
 rather than to the production of one or only a few mar- 
 ket crops at random. The selection of the crops and 
 their utilization for market or feeding purposes should 
 be determined mainly by the system of farming that is 
 most adapted to the soil of the farm, and the farm 
 should be managed largely with the view of maintain- 
 ing the fertility of the soil. 
 
 359. The Inherent and Cumulative Fertility of Soils. ^^ 
 — There is present in nearly every soil a variable 
 amount of inherent fertility resulting from disintegration 
 and other changes to which soils are subject. In some 
 long-cultivated soils the amount of fertility produced 
 annually by weathering and natural agencies is sufficient 
 to yield from ten to fifteen bushels of wheat per acre. 
 This does not represent the maximum crop-producing 
 power of the soil, but simply the inherent or natural fer- 
 tility. When the natural fertility is reenforced with farm 
 manures and other fertilizers, culmulative fertility is 
 added and maximum yields are secured. In many soils 
 there are large amounts of cumulative fertility or resi- 
 dues from former applications of manure. The crop- 
 producing power of a soil is dependent upon both the 
 inherent and the cumulative fertility, as well as upon 
 the mechanical condition of the soil. In the production 
 
PREPARATION OF SOILS FOR CROPS 305 
 
 of crops, all of the inherent fertility should be utilized to 
 the best advantage, and cumulative fertility should be 
 added so that the stock of total fertility may be increased. 
 Soils of the highest fertility are those which are com- 
 posed of a large amount of silt or particles of equivalent 
 value, well drained, but sufficiently retentive of mois- 
 ture for crop production, and of good capillarity. Such 
 soils are usually deposited by water ; they are uniform 
 in texture, of great depth, and contain large amounts of 
 organic matter rich in nitrogen and minerals contain- 
 ing all of the essential elements of plant food. When 
 these soils are cultivated, the organic matter readily 
 undergoes decay with liberation of plant food. 
 
 360. Balanced Soil Conditions. — A high state of 
 fertility necessitates a balanced condition of the phys- 
 ical and chemical properties of a soil. Some soils are 
 of good texture and have all the necessary physical 
 requisites for crop production, but fail to produce good 
 crops because of a scant supply of the essential elements 
 of plant food. Other soils contain the necessary plant 
 food but are unproductive because of poor physical 
 condition. Soils may be unproductive on account of 
 either chemical or physical defects, causing the various 
 factors of soil fertility to be unbalanced. In the cul- 
 tivation of a soil it should be the aim to discover any 
 defect and then to apply the necessary corrective 
 measures. Soil problems are extremely varied in char- 
 acter, and the cultivator of the soil should seek aid jointly 
 
 X 
 
306 SOILS AND FERTILIZERS 
 
 from chemistry, physics, biology, and geology, and also 
 from practical experience founded upon observation in 
 the cultivation of soils and the production of crops. 
 The utilization and maintenance of the fertility of the 
 soil of necessity form the basis of any rational agricul- 
 tural system. 
 
CHAPTER XIV 
 
 LABORATORY PRACTICE 
 
 The laboratory practice is an essential part of the work in Soils 
 and Fertilizers, as the experiments illustrate many of the funda- 
 mental principles of the subject. The student should endeavor to 
 cultivate his powers of observation so as to grasp the principles in- 
 volved in the work rather than to do it in a merely mechanical or 
 perfunctory way. Neatness is one of the essentials for success in 
 laboratory practice ; an experiment performed in a slovenly manner 
 is of but little value. 
 
 A careful and systematic record of the laboratory work should be 
 kept by the student in a suitable note-book. In recording the re- 
 sults of an experiment, the student should give in a clear and con- 
 cise form the following : 
 
 (i) Title of the experiment. 
 
 (2) How the experiment is performed. 
 
 (3) What was observed. 
 
 (4) What the experiment proves. 
 
 The note-book should be a complete record of the student's in- 
 dividual work, and should be written up at the time the experiment 
 is performed. 
 
 Before an experiment is made the student is advised to review 
 those topics presented in the text which have a bearing upon the 
 experiment, so a clearer conception may be gained of the relation- 
 ship between the laboratory work and that of the class room. 
 
 Students who have had but little laboratory practice are advised 
 to study the chapters on Laboratory Manipulation, and Water and 
 Dry Matter, in "The Chemistry of Plant and Animal Life." 
 
 307 
 
3o8 
 
 SOILS AND FERTILIZERS 
 
 Some of the pieces of apparatus are loaned to the student when 
 needed to perform the experiment ; for these a receipt is taken, and 
 he is credited with the apparatus when it is returned. 
 
 The following are supplied to each student : — 
 
 I Crucible Tongs. 
 
 I Pkg. Filter Paper. 
 
 I Test Tube Clamp. 
 
 I Evaporator. 
 
 I Stirring Rod. 
 
 3 Beakers. 
 
 6 Test Tubes. 
 
 I Test Tube Stand. 
 
 I Funnel. 
 
 I Mortar and Pestle. 
 
 No. 
 
 I 
 
 2 Bottles. 
 
 No 
 
 II 
 
 2 
 
 I Large Cjlinder. 
 
 
 12 
 
 3 
 
 I Sand Bath. 
 
 
 13 
 
 4 
 
 I Hessian Crucible 
 
 
 14 
 
 5 
 
 I Wooden Stand. 
 
 
 15 
 
 6 
 
 I Tripod 
 
 
 i6 
 
 7 
 
 I Ring Stand and 
 
 3 Rings- 
 
 17 
 
 8 
 
 I Single Clamp. 
 
 
 i8 
 
 9 
 
 I Burner and 2 Ft. 
 
 Rubber 
 
 
 
 
 Tubing. 
 
 
 »9 
 
 
 I Brush. 
 
 
 20 
 
 Directions for Weighing. — Place the dish or material to be 
 weighed in the left hand pan of the balance. (See Fig. 51.) With 
 the forceps lay a weight from the weight box on the right hand pan. 
 Do not touch the weights with the hands. If the weight selected is 
 too heavy, replace it with a lighter weight. Add weights until the 
 pans are counterpoised ; this will be indicated by the needle swing- 
 ing nearly as many divisions on one side of the scale as on the other. 
 The brass weights are the gram weights. The other weights are 
 fractions of a gram. The 500, 200, 100 mg. (milligram) weights are 
 recorded as .5, .2, and .1 gm. The 50, 20, and 10 mg. weights 
 as 0.05, 0.02, and o.oi gm. If the 10, and 2 gm. and the 200, the 
 100, and the 50 gm. weights are used, the resulting weight is 
 12.35 gnis. No moist substance should ever come in contact with 
 the scale pans. The weights and forceps should always be replaced 
 in the weight box. Too much care and neatness cannot be exer- 
 cised in weighing. 
 
 General Direction for Laboratory Practice. — The student should 
 write up the results of his experiments at the time they are per- 
 
LABORATORY PRACTICE 
 
 509 
 
 formed. Careful attention should be given to the spelling, language, 
 and punctuation, and the note-book should represent the student's in- 
 dividual work. He who attempts to cheat in laboratory work by 
 copying the results of others only cheats himself. Care should be 
 exercised to prevent anything getting into the sinks that will clog 
 
 Fig. 51. Balance and Weights. 
 
 the plumbing; soil, matches, broken glass, and paper should be de- 
 posited in the waste jars. The student should learn to use his 
 time in the laboratory profitably and economically. He should ob- 
 tain a clear idea of what he is to do, and then do it to the best of 
 his ability. If the experiment is not a success, repeat it. While 
 the work is in progress it should be given undivided attention. 
 
3IO 
 
 SOILS AND FERTILIZERS 
 
 Experiment No. i 
 Determination of the Hydroscopic Moisture and Volatile Matter of 
 
 Soils 
 
 Fig. 52. Apparatus for determining Moisture Content of Soils. 
 
 Weigh in grams to the second decimal place a dry Hessian 
 crucible. Place 5 to 10 gms. of air-dried soil in the crucible 
 
LABORATORY PRACTICE 
 
 311 
 
 and weigh again. Then place the dish containing the soil in the 
 water oven and leave it four hours for the soil to dry. Cool and 
 weigh at once so there may be as 
 little absorption of water from the 
 air as possible. From the loss of 
 weight, calculate the per cent of 
 hydroscopic moisture in the soil. 
 Place the crucible containing the 
 dry soil in a muffle furnace and 
 leave until all of the organic mat- 
 ter is volatilized. After the cru- 
 cible has cooled on an asbestos 
 mat, weigh and calculate the per 
 cent of volatile matter. The vola- 
 tile matter consists of organic mat- 
 ter and water that is held in chemi- 
 cal combination with the silicates. 
 (Soils from the students' home 
 farms are to be used in Experi- 
 ments Nos. I, 2, 4, 6, 9, 12, 16, 18, 
 19, and 21, each student working 
 
 with his own soil.) Fig. 53. Muffle Furnace used for de- 
 
 termining Volatile Matter. 
 
 Experiment No. 2 
 
 Determination of the Capacity of Loose Soils to absorb Water 
 
 To 100 gms. of air-dried soil in a beaker add 100 cc. of water. 
 Mix the soil and water, then pour the mixture on a saturated 
 but not dripping filter paper fitted into a funnel. For transfer- 
 ring the soil, 50 cc. more water may be used. Measure the drain 
 water in a graduate. To prevent evaporation, keep the moist soil 
 in the funnel covered with a glass plate. Deduct the leachings 
 from the total water used. Calculate the per cent of water retained 
 by the air-dried soil. 
 
312 
 
 SOILS AND FERTILIZERS 
 
 Repeat the experiment, using sand, and note the difference in 
 absorptive power. 
 
 Repeat, using 95 per cent of sand and 5 per cent of dry and 
 finely pulverized manure. 
 
 Experiment No. 3 
 Determination of the Capillary Water of Soils 
 
 For this experiment a sample of soil directly from the field is 
 
 to be used. The .sample is to be 
 taken at a depth of from 3 to 9 
 inches or at any depth desired. 
 One hundred grams of soil are 
 weighed into a tared drying pan, 
 exposed in a thin layer to the room 
 temperature for 24 hours and then 
 reweighed. After an interval of 
 from two to four hours the soil is 
 weighed again, and if the weight is 
 fairly constant, the per cent of water 
 lost by air drying, representing the 
 capillary water of the soil at the time 
 of sampling, is calculated. This ex- 
 periment may be repeated, using 
 different types of soil, as sand, clay, 
 and loam. 
 
 Experiment No. 4 
 
 Capillaiy Action of Water upon 
 Soils 
 
 The Capillary Water of firmly tie a piece of linen cloth 
 
 yoiis. over the end of a long glass tube 
 
 4 inches in diameter, then fasten a piece of wire gauze over 
 the cloth. Fill the tube with sandy soil (No. I). Compact the soil 
 
 Fig. 54. 
 
LABORATORY PRACTICE 313 
 
 after the addition of each measured quantity by allowing the weight 
 from the compaction machine (see Experiment No. 8) to drop twice 
 from the 12-inch mark. 
 
 In a similar way, fill a second and a third tube with clay 
 and loam respectively ; immerse the lower ends of the tubes in 
 a cylinder of water and support the tubes, as shown in the illus- 
 tration. Measure each day for one week the height to which the 
 water rises in the soils. If desired, three more tubes filled loosely 
 with the soils may be added, and the influence of compaction 
 upon the capillary rise of water in the soils noted. 
 
 Experiment No. 5 
 
 Influence of Manure and Shallow Surface Cultivation upon the 
 Moisture Content and Temperature of Soils 
 
 Weigh and fill four boxes, each a foot square and a foot deep, 
 as follows : one with air-dried sand, one with clay, one with loam, and 
 one with sand containing 5 per cent of fine dry manure. Deter- 
 mine the hydroscopic moisture of each sample. Weigh the boxes 
 after adding the soils which should be moderately compacted. To 
 each add the same amount of water slowly from a sprinkling pot, 
 carefully measuring the water used. The soil should be well mois- 
 tened, but not supersaturated. Each box is to receive shallow sur- 
 face cultivation, using for the purpose a gardener's small tool. Leave 
 the boxes exposed to the sun or in a moderately warm room. At the 
 end of one or two days take a sample of soil from the center of 
 each box at a depth of 4 to 8 inches and determine the moisture 
 content as directed in Experiment No. i. Note the differences in 
 moisture content. Weigh the boxes. Take the temperature of the 
 soil in each box. 
 
 Experiment No. 6 
 Weight of Soils 
 
 Determine the cubic contents of a box about 4 inches square. 
 Weigh the box. Determine its weight when filled, not compacted, 
 
314 
 
 SOILS AND FERTILIZERS 
 
 ■with air-dry sand, with clay, with loam, and with peaty soil. Com- 
 pute the weight per cubic foot of each soil. Calculate the weight 
 
 of water held by the 
 box. Determine the ap- 
 parent specific gravity. 
 
 Experiment No. 7 
 Influence of Color upon 
 the Temperature of 
 Soils 
 
 Expose to the sun's 
 rays, dry clay, dry sand, 
 and moist and dry peat. 
 After two hours' expo- 
 sure take the tempera- 
 ture of each. The bulb 
 of the thermometer 
 should be just covered 
 with the soil. All of 
 
 l-'ii^. 55- 
 
 Determining the Weight per Cubic Foot 
 of Soils. 
 
 the observations should be made under uniform conditions. 
 
 Experiment No. 8 
 
 Movement of Air through Soils 
 
 Fill, without compacting, a soil tube 12 inches high and 3 inches 
 in diameter with sifted loam soil. Nearly fill the outer cylinder with 
 water, open the stopcock, and allow the inner cylinder to sink in 
 the water, close the stopcock and connect the aspirator to the soil tube 
 with a rubber tube. Adjust the weight, 2, open the stopcock, and 
 note the time required for 5 liters of air to aspirate through the soil. 
 -In like manner fill tubes with sand, gravel, peat, and clay, and deter- 
 mine the time required for 5 liters of air to be aspirated through 
 each. In filling the tubes, care should be taken that all are treated 
 alike. Repeat the experiment, using soil from your own farm loosely 
 
LABORATORY PRACTICE 
 
 315 
 
 filling one tube, and moderately compacting another with the com- 
 pacting machine. Note the difference in time required for the air 
 to pass through the loose and the compacted soil. 
 
 
 1[ 
 
 T 
 
 i 
 
 
 Fig. 56. Aspirator for determining the Rate of Movement of Air through Soils. 
 (Adapted from Bui. 107, U. S. Dept. Agr., Office of Expt. Stations.) 
 
 Experiment No. 9 
 Separation of Sand, Silt, and Clay 
 
 For this experiment the student should use some of the soil from 
 his home farm. Ten grams of air-dried and crushed soil which have 
 
3i6 
 
 SOILS AND FERTILIZERS 
 
 been passed through a sieve with holes 0.5 mm. in diameter are 
 placed in a mortar and about 20 cc. of water added. The soil is 
 pestled with a rubber-tipped pestle with the object of separating 
 adhering particles without pulverizing the individual soil grains. 
 After two or three minutes' pestling, more water is added and the 
 soil and water are allowed to sediment for about one minute ; the 
 turbid liquid is then decanted into a bealcer. This process of soft 
 
 pestling and decan- 
 tation is repeated 
 two or three times 
 until the remaining 
 soil grains appear 
 free from adhering 
 smaller particles. 
 With some .soils 
 this is a tedious 
 process. The con- 
 tents of the mortar 
 are then transferred 
 to the beaker and 
 enough water added 
 
 Fig. 57. The MechanK-al Analysis of So.is. ^^ ^^^^^^ ^jl ^he 
 
 beaker. The contents of the beaker are thoroughly stirred, and after 
 two or three minutes' sedimentation, the turbid liquid is decanted 
 into a second beaker, leaving the sediment in the first beaker. More 
 water is added to the first beaker, and the stirring, sedimentation, 
 and decantation are repeated until the sediment consists mainly of 
 clean fine sand. After about ten minutes the turbid liquid in the 
 second beaker is decanted into a large cylinder, the sediment in the 
 beaker being washed with more water and the washings added to the 
 cylinder. It is to be noted that the sediment in the second beaker 
 is composed of finer particles than the sediment in the first beaker. 
 The sediment in the first beaker consists mainly of medium and fine 
 sand, and in the second beaker of fine sand and coarse silt. Some 
 
LABORATORY PRACTICE 
 
 317 
 
 sand particles are carried along in the washings into the large cylinder. 
 It is difficult to make even an approximate separation of a soil into 
 sand, silt, and clay particles. In the mechanical analysis of soil, the 
 chemist uses the microscope 
 to determine when the sepa- 
 rations are reasonably com- 
 plete. The sediment in the 
 cylinder consists mainly vi 
 silt. The fine particles whicli 
 remain suspended in the water 
 of the cylinder and cause the 
 roiled appearance are mainly 
 the clay particles. In this 
 experiment note approxi- 
 mately what grades of soil 
 particles predominate 1h your 
 soil. Save the liquid in the 
 cylinder for the next experi- 
 ment. 
 
 Experiment No. 10 
 Sedimentation of Clay 
 
 In each of three separate 
 cylinders or beakers place 
 200 cc. of the turbid liquid 
 saved from Experiment No. 
 9. To beaker No. I. add 0.5 
 gm. calcium hydroxide and Fig. 58. Movement of Water through Soils, 
 stir. To beaker No. 2, add 
 
 I gm. of calcium hydroxide and stir. The third beaker is used for 
 purposes of comparison and no calcium hydroxide is added. After 
 24 hours examine the three beakers and note the influence of the 
 calcium hydroxide in precipitating the clay and clarifying the liquid. 
 
3l8 SOILS AND FERTILIZERS 
 
 Experiment No. ii 
 Deportment of Soils when Wet 
 
 Place about 5 gms. of the soil used in Experiment No. 9 in the 
 palm of the hand. Wet and knead. Note whether a plastic mass 
 is formed. If the soil is sticky, it indicates the presence of plastic 
 clay. Rub some of the soil between thumb and finger ; if it is com- 
 posed largely of clay, it will feel smooth and oily. The sand parti- 
 cles impart a sharp gritty feeling ; in the presence of clay this is more 
 or less modified. Note wliether the lumps of dry soil crush easily. 
 The way a soil responds when crushed, wet, and kneaded, gives 
 some idea of its tillage properties. 
 
 Experiment No. 12 
 Rate of Movement of Water through Soils 
 
 Weigh a soil tube and fill it to within two inches of the top with 
 sand. Weigh again. In like manner weigli and fill two other 
 tubes, one with clay and one with loam. Support the tubes from 
 the ring stand as noted in Fig. No. 58. Place a receptacle under 
 the outlet of each tube. Measure into cylinders or large beakers 
 three 500 cc. portions of water. From one of these beakers slowly 
 pour the water into the sand cylinder, and note the length of time 
 required for the water to percolate through the sand, and the amount 
 of water that percolates in a given time. Replenish the water in 
 the beaker with measured amounts as needed. In like manner test 
 the clay and the loam. After the water has ceased dripping from 
 the tubes, weigh and calculate the amount retained by the soils. 
 
 Experiment No. 13 
 
 Properties of Rocks from which Many Soils are Derived 
 
 Study the laboratory samples of rocks and fill out the following 
 table : — 
 
LABORATORY PRACTICE 
 
 319 
 
 Rocks 
 
 Comparative 
 Hardness 
 
 Color 
 
 General 
 
 Form 
 
 Soluble 
 IN HCl 
 
 Feldspar . . . 
 
 Mica 
 
 Quartz .... 
 Granite .... 
 Hornblende . . . 
 Limestone . . 
 
 
 
 
 
 Experiment No. 14 
 Form and Size of Soil Particles 
 (Note. Special directions for manipulating the microscope, plac- 
 ing the material on the microscopical object slide, and focusing will 
 be given by the instructor.) 
 
 Place on a microscopical object slide a small amount of soil ; dis- 
 tribute it in a thin layer, and examine with a low-power microscope. 
 Observe the form and size of the soil particles, distinguish the vari- 
 ous grades of sand, silt, and clay, and make drawings of some of the 
 particles. 
 
 Experiment No. 15 
 
 Pulverized Rock Particles 
 
 I Examine with a low-power microscope samples of pulverized 
 I mica, feldspar, granite, and limestone. Note any similarity to the 
 I soil particles examined in Experiment No. 14. 
 
 i Experiment No. 16 
 
 I Reaction of Soils 
 
 For this experiment use peaty, mildly alkaline, and clay soils. 
 
 j Bring in contact with each soil, after moistening with distilled 
 
 ( water, pieces of sensitive red and blue litmus paper. Note any 
 
 j changes in color of the litmus paper and state what the results show. 
 
 I In a similar way test the soil from your own farm. 
 
320 SOILS AND FERTILIZERS 
 
 Experiment No. 17 
 Absorption of Gases by Soils 
 Weigh 50 gms. of soil into a wide-mouthed bottle, add 50 cc. of 
 water and i cc. of strong ammonia. Note the odor. Cork the 
 bottle, shake, and after 24 hours again note the odor. To what is 
 the fixation of the ammonia due.-* Is this a physical or a chemical 
 change? Define fi.xation. 
 
 Experiment No. 18 
 Acid Insoluble Matter of Soils 
 Weigh 10 gms. of soil into a beaker, add 100 cc. hydrochloric 
 acid (50 cc. strong acid and 50 cc. H2O) ; cover the beaker with a 
 watch glass; heat on the sand bath in the hood for two hours, re- 
 placing the acid solution in case excessive evaporation takes place. 
 Filter, transfer, and wash the residue, using 50 cc. distilled water. 
 Note the appearance and quantity of insoluble residue. Of what 
 does it consist? What is its value as plant food? How does it 
 resemble the original soil and in what ways does it differ? Save 
 the filtrate for the next experiment. 
 
 Experiment No. 19 
 Acid Soluble Matter of Soils 
 Divide the filtrate from the preceding experiment into three 
 equal portions, (i) To one portion add ammonia until alkaline. 
 The precipitate formed consists of iron and aluminum hydroxide and 
 phosphoric acid. Note the color and gelatinous appearance of this 
 precipitate. When dried it occupies only a small volume. Filter 
 and remove this precipitate which contains lime, magnesia, potasli. 
 and soda. To the filtrate add 20 cc. of ammonium oxalate ; warm 
 on the sand bath, and note any precipitate of calcium oxalate 
 that is formed. (2) Evaporate the second portion nearly to dry- 
 ness. Add"20 cc. distilled H^O and 3 cc. HNO3; warm to dissolve 
 
LABORATORY PRACTICE 321 
 
 any residue. Add 5 to 7 cc. of ammonium molybdate, heat gently, 
 and shake. The yellow precipitate is ammonium phosphomolyb- 
 date, which contains the element P in mechanical and chemical com- 
 bination. (3) Evaporate the third portion in the evaporating dish 
 on the sand bath. Of what does the residue consist and what 
 elements does it contain? 
 
 9 
 
 Experiment No. 20 
 Extraction of Humus from Soils 
 
 Place 10 gms. of soil in a bottle (preferably a glass-stop- 
 pered one) and add 200 cc. HgO and 5 cc. HCl. Shake and allow 
 10 to 24 hours for the acid to dissolve the lime so the humus 
 can be dissolved by the alkali. Filter the acid and wash the soil 
 on the filter with distilled water until the washings are no longer 
 acid to litmus paper. Transfer the soil to the bottle again, add 
 100 cc. HgO and 5 cc. KOH solution. Shake, and after two to 
 four hours filter off some of the solution which is dark-colored 
 and contains dissolved humus compounds. 
 
 To 10 cc. of the filtered humus solution add HCl until neutral. 
 The precipitate formed is mainly humic acid and soil humates. 
 Evaporate a second portion of 10 to 20 cc. to dryness ; the black 
 residue obtained is humus material extracted from the soil. 
 
 Experiment No. 21 
 Nitrogen in Soils 
 Mix 5 gms. of soil and an equal bulk of soda lime in a mortar; 
 transfer to a strong test tube. Connect the test tube with a deliv- 
 ery tube which leads into another test tube containing distilled 
 water. Heat cautiously for from 5 to 10 minutes, with the Bunsen 
 burner, the test tube containing the soil and soda lime. Test the 
 liquid with litmus paper and note the reaction. Soda hme aided 
 by heat decomposes the organic matter of the soil and forms COg, 
 H2O, and NH3. The nitrogen in the form of ammonia is distilled 
 
 Y 
 
322 
 
 SOILS AND FERTILIZERS 
 
 and absorbed by the water in the second test tube; the reaction 
 is due to the presence of the ammonia. 
 
 Experiment No. 22 
 
 Testing for Nitrates 
 
 Dissolve about 50 milligrams of sodium or potassium nitrate in 
 
 100 cc. H^,0. To 15 cc. 
 of this solution add 2 cc. 
 of a dilute and clear solu- 
 tion of FeSO^, and place 
 the test tube in a cylinder. 
 Through a long-stemmed 
 funnel add 2 or 3 cc. HgSO^. 
 Observe the dark brown 
 ring that is formed ; H2S0^ 
 liberates HNO3 as a free 
 acid, which in turn changes 
 the iron from the ferrous 
 to the ferric state ; the dark 
 brown color is due to the 
 nitric acid forming interme- 
 diate compounds during 
 this operation. 
 
 Fig. 59. Testing for Nitrates. 
 
 Experiment No. 23 
 
 Volatilization of Ammonium Salts 
 
 In separate test tubes place about o.i gm. each of ammonium 
 carbonate and ammonium sulphate. Apply heat gently to each and 
 observe the result. Observe that the ammonium carbonate readily 
 volatilizes and some is deposited on the walls of the test tube while 
 the ammonium sulphate is much less volatile. In poorly ventilated 
 barns, deposits of ammonium carbonate are frequently found. 
 
 J 
 
i 
 
 LABORATORY PRACTICE 
 
 323 
 
 Add slowly and 
 
 Experiment No. 24 
 Testing for Phosphoric Acid 
 
 Dissolve 0.5 gm. bone ash in 15 cc. H2O and 3 to 5 cc. HNO^and 
 filter. To the warm filtrate add 5 to 7 cc. ammonium molybdate 
 and shake. The yellow precipitate formed is ammonium phospho- 
 molybdate. See Experiment No. 19. 
 
 In a test tube heat 0.5 gm. of bone ash with 20 cc. distilled 
 H„0; filter. To the warm filtrate add 5 cc. ammonium molyb- 
 date and shake. Note the result as compared with that when 
 HNO3 was used with the distilled water. What does the result 
 show ? 
 
 Experiment No. 25 
 Preparation of Acid Phosphate 
 
 Place 100 gms. bone ash in a large lead dish, 
 with constant stirring loo gms. commercial 
 sulphuric acid, using an iron spatula for the 
 purpose. Transfer the mixture to a wooden 
 box and allow it to act for about th-ree days. 
 Then pulverize and examine. The mixing of 
 the acid and phosphate should be done in a 
 place where there is a good draft. Test { 
 gm. for water soluble phosphates as directed 
 in Experiment No. 24. 
 
 Experiment No. 26 
 
 Solubility of Organic Nitrogenous Compounds 
 in Pepsin Solution 
 
 Prepare a pepsin solution by dissolving 
 5 gms. of commercial pepsin in a liter of 
 water, adding i cc. of strong HCl. Place in 
 separate beakers 0.5 gm. each of dried blood, 
 tankage, and bone ash. Add 200 cc. of pep- 
 sin solution to each and place the beakers in a 
 
 Fig. 60. Determining 
 Digestibility of Organic 
 Nitrogen in Acid Pepsin 
 Solution. 
 
324 SOILS AND FERTILIZERS 
 
 water bath kept at a temperature of about 40° C. Stir occasion- 
 ally, and at the end of five hours observe and compare the amounts 
 of insoluble matter remaining in the beakers, note also the color 
 and appearance of the solution in each beaker. See Section 170. 
 
 Experiment No. 27 
 
 Preparation of Fertilizers 
 
 Mix in a box 200 gms. acid phosphate (saved from Experiment 
 No. 25), 50 gms. kainit, and 50 gms. sodium nitrate. Calculate the 
 percentage composition of this fertiUzer and its trade value. 
 
 Experiment No. 28 
 
 Testing Ashes 
 
 Test samples of leached and unleached ashes in the way de- 
 scribed in Section 256. 
 
 Experiment No. 29 
 
 Extracting Water Soluble Materials from a Commercial Fertilizer 
 
 Dry and weigh a 7 cm. filter paper. Fit it in a funnel, and place 
 in it 2 gms. of commercial fertilizer. Pass through the filter, a little 
 at a time, a half liter of pure water at about 40° C. (distilled 
 water preferred). Transfer the filter paper and contents to a watch 
 glass, dry in a water oven, weigh and calculate the per cent of 
 material extracted by the water. If the fertilizer is made of such 
 materials as acid phosphate, kainit, muriate or sulphate of potash, 
 nitrate of soda and sulphate of ammonia, from 60 to 90 per cent 
 will dissolve. Inspect the insoluble residue and note if it is 
 composed of dried blood, bones, or animal refuse material. Of a 
 high-grade complete commercial fertilizer from 40 to 80 per cent 
 or more should dissolve in water. 
 
LABORATORY PRACTICE 325 
 
 Experiment No. 30 
 
 Influence of Continuous Cultivation and Crop Rotation upon the 
 Properties of Soils 
 
 For this experiment a soil that has been under continuous culti- 
 vation, and also one of similar character from an adjoining field 
 where the crops have been rotated and farm manures have been 
 applied, should be used. Make the following determinations with 
 each soil : — 
 
 Weight per cubic foot. 
 
 Capacity to hold water. 
 
 Note the color of each. 
 
 Experiment No. 31 
 Summary of Results of Tests with Home Soil 
 
 Make a tabulation of your results including : 
 
 Hydroscopic moisture as determined in Experiment No. i. 
 
 Volatile matter as determined in Experiment No. i. 
 
 Capacity of the loose soil to absorb water. Experiment No. 2. 
 
 Height of rise of capillary water in tube, Experiment No. 4. 
 
 Weight per cubic foot, Experiment No. 6. 
 
 Prevailing kind of soil particles. Experiment No. 9. 
 
 Deportment of soil when wet and kneaded. Experiment No. 11. 
 
 Reaction of soil. Experiment No. 16. 
 
 Amount of acid soluble matter. Experiment No. 19. 
 
 Amount of lime. Experiment No. 19. 
 
 Amount of humus extractive material, Experiment No. 20. 
 
 Crops most suitable for production upon this soil as indicated by 
 physical and chemical tests. 
 
 How does this agree with your experience with the crops raised 
 on the soil ? 
 
 Probable deficiencies or weak points as indicated by tests or past 
 experience. 
 
 What is the most suitable line of farming to follow with this soil 
 in order to conserve its fertility? 
 
326 SOILS AND FERTILIZERS 
 
 Scheme of Soil Classification 
 
 (Adapted from Bureau of Soils Report, U. S. Dept. Agr.) 
 
 Coarse sand contains more than 20 per cent of coarse sand and 
 more than 50 per cent of fine gravel, coarse sand, and medium sand, 
 less than 10 per cent of very fine sand, less than 15 per cent of silt, 
 less than 10 per cent of clay, and less than 20 per cent of silt and 
 clay. 
 
 Medium sand contains less than 10 per cent of fine gravel, more 
 than 50 per cent of coarse, medium, and fine sand, less than 10 per 
 cent of very fine sand, less than 15 per cent of silt, less than 10 per 
 cent of clay, and less than 20 per cent of silt and clay. 
 
 Fine sand contains less than 10 per cent of fine gravel and 
 coarse sand, more than 50 per cent of fine and very fine sand, less 
 than 15 per cent of silt, less than 10 per cent of clay, and less than 
 20 per cent of silt and clay. 
 
 Sandy loam contains more than 20 per cent of fine gravel, coarse 
 sand and medium sand, more than 20 per cent and less than 35 
 per cent of silt, less than 15 per cent of clay, and less than 50 per 
 cent of silt and clay. 
 
 Fine sandy loam contains more than 40 per cent of fine and 
 very fine sand and more than 20 per cent and less than 50 per cent 
 of silt and clay, usually 10 to 35 per cent of silt and from 5 to 15 
 per cent of clay. 
 
 Silt loam contains more than 55 per cent of silt and less than 25 
 per cent of clay. 
 
 Loam contains less than 55 per cent of silt and more than 50 
 per cent of silt and clay, usually from 15 to 25 per cent of clay. 
 
 Clay loam contains from 25 to 55 per cert of silt, 25 to 35 per 
 cent of clay, and more than 60 per cent of silt and clay. 
 
 Clay contains more than 35 per cent of clay. 
 
 Sandy clay contains more than 30 per cent of coarse, medium, 
 and fine sand, less than 25 per cent of silt, more than 20 per cent of 
 clay, and less than 60 per cent of silt and clay. 
 
 Silt clay contains more than 55 per cent of silt and from 25 to 35 
 per cent of clay. 
 
REVIEW QUESTIONS 
 
 CHAPTER I 
 
 I. From what are soils derived ? 2. What are the physical prop- 
 erties of soils ? When do soils differ physically, when chemically ? 
 3. Why do soils differ in weight ? Arrange clay, sand, loam, and 
 peat in order of weight per cubic foot. 4. When wet, what would 
 be the order? 5. What is the absolute and what the apparent 
 specific gravity of soils ? What is pore space? 6. Define the terms : 
 skeleton, fine earth, fine sand, silt, and clay. 7. What are the 
 physical properties of clay ? 8. What are the forms of the soil 
 particles ? 9. How do different types of soil vary as to the number 
 of particles per gram of soil ? 10. How is a mechanical analysis 
 of a soil made ? 11. Why do certain crops thrive best on definite 
 types of soil ? 12. What factors must be taken into consideration 
 in determining the type to which a soil belongs ? 13. Give the 
 mechanical structure of a good potato soil. 14. How does a wheat 
 soil differ in mechanical structure from a truck soil? 15. A good 
 corn soil is also a type for what other crops ? 16. How much 
 water is required to produce an average grain crop, and how do the 
 rainfall and the water removed in crops during the growing season 
 compare ? 17. In what forms may water be present in soils ? 18. 
 What is bottom water and when may it be utilized by crops ? 19. 
 What is capillary water ? 20. Explain the capillary movement of 
 water. 21. Explain how the capillary and non-capillary spaces in 
 the soil may be influenced by cultivation. 22. What is hydroscopic 
 water and of what value is it to crops ? 23. What is percolation ? 
 24. To what extent may losses occur by percolation ? 25. What 
 are the factors which influence evaporation ? 26. What is transpira- 
 tion ? 27. In what three ways may water be lost from the soil ? 
 28. Why does shallow surface cultivation prevent evaporation ? 
 
 327 
 
328 SOILS AND FERTILIZERS 
 
 29. Why is it necessary to cultivate the soil after a rain ? 30. Ex- 
 plain the movement of the soil water after a light shower. 31 . What 
 influence has rolling the land upon the moisture content of the soil? 
 32. What is subsoiling and how does it influence the moisture 
 content of soils ? 33. What influence does early spring plowing 
 exert upon the soil moisture ? 34. What is the action of a mulch 
 upon the soil ? 35. Why should different soils be plowed to differ- 
 ent depths ? 36. What is meant by the permeability of a soil? 
 37. How may cultivation influence permeability? 38. How may 
 commercial fertilizers influence the water content of soils ? 39. 
 Explain the physical action of well-prepared farm manures upon the 
 soil and their influence upon the soil water. 40. What is the object 
 of good drainage ? 41. Why does deforesting a region unfavorably 
 influence the agricultural value of a country ? 42. What are the 
 sources of heat in soils ? 43. To what extent does the color of 
 soils influence the temperature ? 44. What is the specific heat of 
 soils? 45- To what extent does drainage influence soil tempera- 
 ture and how does cultivation affect soil temperature ? 46. How 
 do manured and unmanured lands compare as to temperature ? 47. 
 What relation does heat bear to crop growth ? 48. What materials 
 impart color to soils ? 49. What is the effect of loss of organic 
 matter upon the color of soils ? 50. What materials impart taste to 
 soils ? Odor ? 51. What effect does a weak current of electricity 
 have upon crop growth ? 52. Do all soils possess the same power 
 to absorb gases ? Why ? 
 
 CHAPTER II 
 
 53. What is agricultural geology ? 54. What agencies have 
 taken part in soil formation ? 55. How does the action of heat, 
 cold, air, and gases aid in soil formation ? 56. Explain the physical 
 action of water in soil formation. Explain its chemical action. 57. 
 What is glacial action, and how has it been an important factor in 
 soil formation ? 58. Explain the action of earthworms and vegeta- 
 tion upon soils. 59. How have micro-organisms aided in soil forma- 
 
REVIEW QUESTIONS 329 
 
 tion ? 60. Explain the terms : sedentary, transported, alluvial, 
 colluvial, volcanic, and wind-formed soils. 61. What is feldspar 
 and what kind of soil does it produce ? 62. Give the general 
 composition of the following rocks and minerals and state the 
 kind of soil which each produces : granite, mica, hornblende, 
 zeolites, kaolin, apatite, and limestone. 
 
 CHAPTER III 
 
 63. What elements are liable to be the most deficient in soils ? 
 64. Name the acid- and base-forming elements present in soils. 65. 
 What are the elements most essential for crop growth ? 66. State 
 some of the different ways in which the elements present in soils 
 combine. 67. Why is it customary to speak of the oxides of the 
 elements and to deal with them rather than with the elements ? 68. 
 Do the elements exist in the soil in the form of oxides ? 69. What 
 are double silicates ? 70. In what forms does carbon occur in soils .'' 
 71. Is the soil carbon the source of the plant carbon ? 72. What 
 can you say regarding the occurrence and importance of the sulphur 
 compounds ? 73. What influence would o.io per cent chlorine have 
 upon the soil ? 74. In what forms does phosphorus occur in 
 soils? 75. What is the principal form in which nitrogen occurs 
 in soils ? 76. What can be said regarding the hydrogen and 
 oxygen of the soil ? ']']. State the principal forms and the value as 
 plant food of the following elements : aluminum, potassium, calcium, 
 sodium, and iron. 78. For plant-food purposes, what three 
 divisions are made of the soil compounds ? 79. Why are the 
 complex silicates of no value as plant food ? 80. Give the relative 
 amounts of plant food in the three classes. 81. How is a soil 
 analysis made ? 82. What can be said regarding the economic 
 value of a soil analysis ? 83. What are some of the important facts 
 to observe in interpreting results of soil analysis ? 84. Under what 
 conditions are the results most valuable ? 85. Do the terms ' volatile 
 matter' and 'organic matter' mean the same ? 86. How may organic 
 acids be employed in soil analysis ? 87. Why are dilute organic 
 
330 SOILS AND FERTILIZERS 
 
 acids used ? 88. Is the plant food equally distributed in both sur- 
 face and subsoil ? 89. Do different grades of soil particles, from 
 the same soil, have the same composition? 90. What are 'alkali 
 soils'? 91. Why is the alkali sometimes in the form of a crust? 
 What is black alkali ? 92. Are all soils with white coating strongly 
 alkaline? 93. Give the treatment for improving an alkali soil. 94. 
 How may a small 'alkali spot' be treated? 95. What are the 
 sources of the organic compounds of soils ? What are acid soils ? 
 96. How may the organic compounds of the soil be classified ? 97. 
 Explain the term 'humus.' 98. How is the humus of the soil ob- 
 tained ? 99. What is humification ? What is a humate ? How 
 are humates produced in the soil ? 100. Explain how different 
 materials produce humates of different value. loi. Arrange in 
 order of agricultural value the humates produced from the following 
 materials : oat straw, sawdust, meat scraps, sugar, clover. 102. Of 
 what value are the humates as plant food ? 103. How much plant 
 food is present in soils in humate forms ? 104. What agencies cause 
 a decrease of the humus content of soils ? 105. To what extent 
 does humus influence the physical properties of soils ? 106. What 
 is humic acid ? 107. What soils are most liable to be in need 
 of humus? When are soils not in need of humus ?_ 108. In what 
 ways does the humus of long-cultivated soils differ from that of new 
 soils ? 109. How may different methods of farming influence the 
 humus content of soils ? 
 
 CHAPTER rV 
 
 110. What may be said regarding the importance of nitrogen as 
 plant food ? in. What are the functions of nitrogen in plant nu- 
 trition ? 112. How may the foliage indicate a lack or an excess of 
 this element ? 113. In what three ways did Boussingault conduct 
 experiments relating to the assimilation of the free nitrogen of the 
 air? 114. What were his results? 115. What conclusions did 
 Ville reach ? 116. Give the results of Lawes and Gilbert's experi- 
 ments. 117. How did field results compare with laboratory experi- 
 
REVIEW QUESTIONS 331 
 
 ments ? Ii8. In what ways were the conditions of field experi- 
 ments different from those conducted in the laboratory ? 119. Give 
 the results of Hellriegel's and Wilfarth's experiments. 120. What 
 is noticeable regarding the composition of clover-root nodules ? 121. 
 Of what agricultural value are the results of Hellriegel ? 122. What 
 is the source of the soil's nitrogen ? 123. How may the organic 
 nitrogen compounds of the soil vary as to complexity? 124. To 
 what extent may the nitrogen in soils vary ? 125. To what extent 
 is nitrogen removed in crops? 126. To what extent are nitrates, 
 nitrites, and ammonium compounds found in soils ? 127. To what 
 extent is nitrogen returned to the soil in rain water ? 128. How 
 may the ratio of nitrogen to carbon vary in soils ? Of what agricul- 
 tural value is this ratio ? 129. Under what conditions do soils gain 
 in nitrogen content ? 130. What methods of cultivation cause the 
 most rapid decline in the nitrogen content of soils, and how can a 
 nitrogen equilibrium be maintained in the soil ? 131. What is 
 nitrification ? 132. What are the conditions necessary for nitrifica- 
 tion, and what are the food requirements of the nitrifying organ- 
 ism ? 133. Why is oxygen necessary for nitrification ? 134. How 
 do temperature, moisture, and sunlight influence this process ? 
 135. What part do calcium carbonate and other basic compounds 
 take in nitrification ? 136. How is nitrous acid produced ? 137. 
 What is denitrification ? 138. What other organisms are present in 
 soils besides those which produce nitrates, nitrites, and ammonia ? 
 
 139. What chemical products do these various organisms produce ? 
 
 140. Why are soils sometimes inoculated , with organisms ? When 
 is this necessary and when is it not ? 141. Why does summer 
 fallowing of rich land cause a loss of humus and nitrogen ? 142. 
 What influence have deep and shallow plowing, and spring and fall 
 plowing, upon the available soil nitrogen ? 143. Into what three 
 classes are nitrogenous fertiHzers divided ? 144. How is dried blood 
 obtained ? What is its composition, and how is it used ? 145. 
 What is tankage ? How is it used, and how does it differ in com- 
 position from dried blood ? 146. What is flesh meal ? 147. What 
 
332 SOILS AND FERTILIZERS 
 
 is fish-scrap fertilizer, and what is its comparative value ? 148. 
 What seed residues are used as fertilizer ? What is their value ? 
 149. What methods are employed to detect the presence of leather, 
 hair, and wool waste in fertilizers ? Why are these materials objec- 
 tionable ? 150. How may peat and muck be used as fertilizers? 
 151. What is sodium nitrate ? How is it used, and what is its value 
 as a fertilizer? 152. How does ammonium sulphate compare in 
 fertilizer value with nitrate of soda ? What is calcium cyanamid ? 
 153. What is the difference between the nitrogen content and the 
 ammonia content of fertilizers ? 
 
 CHAPTERS V AND VI 
 
 154. What is fixation ? What is absorption ? Give an illus- 
 tration. 155. To what is fixation due ? 156. What part does 
 humus take in fixation ? 157. Why do soils differ in fixative 
 power ? Why are nitrates not fixed ? Explain the fixation of 
 potash, phosphate, and ammonium compounds. 158. Why is fixa- 
 tion a desirable property of soils ? 159. Why is it necessary to 
 study the subject of fixation in the use of manures ? Why is the 
 soil solution dependent upon the fixative power of the soil ? 160. 
 Why are farm manures variable in composition? 161. What is 
 the distinction between the terms 'stable manure' and 'farmyard 
 manure'? 162. About what per cent of nitrogen, phosphoric acid, 
 and potash is present in ordinary manure ? 163. Coarse fodders 
 cause an increase of what element in the manure ? 164. What 
 four factors influence the composition and value of manure ? 165. 
 What influence do absorbents have upon the composition of 
 manures ? 166. What advantages result from the use of peat and 
 muck as absorbents ? 167. Compare the value of manure produced 
 from clover with that from timothy hay. 168. How may the value 
 of manure be determined from the nature of the food consumed ? 
 169. To what extent is the fertility of the food returned in 
 the manure ? 170. Is much nitrogen added to the body during the 
 process of fattening ? 171. Explain the course of the nitrogen of 
 
I 
 
 REVIEW QUESTIONS 333 
 
 the food during digestion and the forms in which it is voided in 
 the manure. 172. Compare the solid and liquid excrements as to 
 constancy of composition and amounts produced. 173. What is 
 meant by the manurial value of food ? 174. Name five foods with 
 high manurial value ; also five with low manurial value. 175. 
 What is the usual commercial value of manures compared with 
 commercial fertilizers ? 176. How does the manure from young 
 and from old animals compare as to value ? 177. How much 
 manure does a well-fed cow produce per day ? 178. What are the 
 characteristics of cow manure ? How do horse manure and cow 
 manure differ as to composition, character, and fermentability ? 
 179. What are the characteristics of sheep manure ? 180. How 
 does hen manure differ from any other manure .'' 181. Why should 
 the solid and liquid excrements be mixed to produce balanced 
 manure? 182. What volatile nitrogen compound may be given off 
 from manure ? 183. What may be said regarding the use of human 
 excrements as manure ? 184. Is there any danger of immediate 
 scarcity of plant food to necessitate the use of human excrements 
 as manure ? 185. To what extent may losses occur when manures 
 are exposed in loose piles and allowed to leach for six months ? 
 186. What two classes of ferments are present in manure ? How 
 does an application of farm manure affect the bacterial content of 
 soil and what influence does this have upon the plant food of the 
 soil ? 187. Explain the workings of the two classes of ferments 
 found in manures. 188. How much heat may be produced in 
 manure during fermentation ? 189. Is water injurious to manure ? 
 190. How should manure be composted ? What is gained ? 191. 
 How does properly composted manure compare in composition with 
 fresh manure ? 192. Explain the action of calcium sulphate in the 
 preservation of manure. 193. How does manure produced in 
 barn yards compare in composition and crop-producing value with 
 that produced in covered sheds ? 194. When may manure be 
 taken directly to the field and spread ? 195. How may coarse 
 manures be injurious to crops ? 196. What is gained by manuring 
 
334 SOILS AND FERTILIZERS 
 
 pasture land ? 197. Is it economical to make a number of small 
 manure piles in a field ? Give reason. 198. At what rate per 
 acre may manure be used ? 199. To what crops is it not advisable 
 to add stable manure ? 200. How do a crop and the manure pro- 
 duced from that crop compare in manurial value ? 201. Why do 
 manures have such a lasting effect upon soils ? 202. Why does 
 manure from different farms vary so much in value and composi- 
 tion ? 203. In what ways may stable manures be beneficial ? 
 
 CHAPTER VII 
 
 204. What may be said regarding the importance of phosphorus 
 as plant food ? What function does it take in plant economy ? 
 205. What is phosphoric acid and how much is removed in ordi- 
 nary farm crops ? 206. To what extent is phosphoric acid present 
 in soils ? 207. What are the sources of the soil's phosphoric acid ? 
 
 208. What are the commercial sources of phosphate fertilizers ? 
 
 209. Name the four calcium phosphates and give their relative fer- 
 tilizer values. 210. Define reverted phosphoric acid. 211. Define 
 available phosphoric acid. 212. In what forms do phosphate 
 deposits occur ? 213. State the general composition of phosphate 
 rock. 214. Explain the process by which acid phosphates are made. 
 Give reactions. 215. How is the commercial value of phosphoric 
 acid determined ? 216. What is basic phosphate slag and what is 
 its value as a fertilizer ? 217. What is guano ? 218. How do raw 
 bone and steamed bone compare as to field value ? As to composi- 
 tion ? 219. What is dissolved bone ? 220. How is bone black 
 obtained, and what is its value as a fertilizer 1 221. How are 
 phosphate fertilizers applied to soils ? In what amounts ? 222. 
 How may the phosphoric acid of the soil be kept in available 
 condition ? 
 
 CHAPTER VIII 
 
 223. What is the function in plant nutrition of potassium ? 224. 
 What is potash and to what extent is it removed in farm crops ? 
 225. To what extent is potash present in soils .'' 226. What are 
 
r REVIEW QUESTIONS 335 
 
 the sources of the soil's potash ? 227. What are the various sources 
 of the potash used for fertilizers ? 228. What are the Stassfurt salts, 
 and how are they supposed to have been formed ? 229. What is 
 kainit ? 230. How much potash is there in hard wood ashes ? 231. 
 In what ways do ashes act on soils ? 232. How do unleached ashes 
 differ from leached ashes ? 233. What is meant by the alkalinity 
 of an ash ? 234. Of what value, as fertilizer, are hard- and soft- 
 coal ashes ? 235. What is the fertilizer value of the ashes from 
 tobacco stems ? 236. Cottonseed hulls ? 237. Peat-bog ashes ? 
 238. Sawmill ashes ? 239. Lime-kiln ashes ? 240. How is the 
 commercial value of potash determined ? 241 . How are potash 
 fertilizers used ? 242. Why is it sometimes necessary to use a lime 
 fertilizer in connection with a potash fertilizer ? 
 
 CHAPTER IX 
 
 243. What can be said regarding the importance of calcium as a 
 plant food ? 244. What is lime, and to what extent is it removed 
 in crops ? 245. To what extent do soils contain lime ? 246. What 
 are the lime fertilizers ? 247. Explain the physical action of lime 
 fertilizers. 248. Explain the action of lime on heavy clays. 249. 
 On sandy soils. 250. In what ways, chemically, do lime fertilizers 
 act? 251. How may Ume aid in liberating potash ? 252. What is 
 marl ? 253. How are lime fertilizers applied ? 254. What is the 
 result when land plaster is used in excess ? 255. Explain the action 
 of salt on soils. 256. When would it be desirable to use salt as a 
 fertilizer ? 257. Is soot of any value as a fertilizer ? Explain its 
 action. 258. Are seaweeds of any value as fertilizer ? What is the 
 fertilizer value of street sweepings ? Of garbage ? 
 
 CHAPTER X 
 
 259. What is a commercial fertilizer? An amendment? 260. 
 To what does the commercial fertilizer industry owe its origin? 
 
 261. Why are commercial fertilizers so variable in composition? 
 
 262. Explain how a commercial fertilizer is made. 263. Why are 
 
336 SOILS AND FERTILIZERS 
 
 analysis and inspection of fertilizers necessary? 264. What are 
 the usual forms of nitrogen in commercial fertilizers? 265. Of 
 phosphoric acid and potash? 266. How is the value of a commer- 
 cial fertilizer determined? 267. What is gained by home mixing 
 of fertilizers? 268. What can be said about the importance of 
 tillage when fertilizers are used? 269. How are commercial fer- 
 tilizers sometimes injudiciously used? 270. How may field tests 
 be conducted to determine a deficiency in available nitrogen, phos- 
 phoric acid, or potash? 271. To determine a deficiency of two 
 elements? 272. How are the preliminary results verified? 273. 
 Why is it essential that field tests with fertilizers be made? 274. 
 Under what conditions does it pay to use commercial fertilizers? 
 275. What is the result when commercial fertilizers are used in 
 excessive amounts? 276. Under ordinary conditions, what special 
 help do the following crops require : wheat, barley, corn, potatoes, 
 mangels, turnips, clover, and timothy? 277. In what ways do 
 commercial fertilizers and farm manures differ? How do they com- 
 pare in crop-producing value ? 
 
 CHAPTER XI 
 
 278. Does the amount of fertility removed by crops indicate the 
 nature of the fertilizer required? In what ways are plant-ash 
 analyses valuable? 279. Explain the action of plants in rendering 
 their own food soluble. To what extent does the soil solution sup- 
 ply plant food ? 280. Why do crops differ as to their power of pro- 
 curing food? 281. Why is vi^heat grown on a clay soil less liable 
 to need potash than nitrogen? 282. What position should wheat 
 occupy in a rotation? 283. In what ways do wheat and barley 
 differ in feeding habits ? 284. What can be said regarding the food 
 requirements of oats? 285. Corn removes from the soil twice as 
 much nitrogen as a wheat crop, yet wheat usually thrives after 
 corn. Why? What help is corn most liable to need in the way 
 of food? 286. What is flax wilt? 287. What position should flax 
 occupy in a rotation? 288. On what soils does flax thrive best? 
 
REVIEW QUESTIONS 337 
 
 289. What is the essential point to observe in the manuring of 
 potatoes? 290. What kind of manuring is required by sugar beets ? 
 291. Why should the manuring of mangels be different from that of 
 turnips? 292. What may be said regarding the food requirements 
 of buckwheat and rape? 293. What kind of manuring do hops and 
 cotton require? 294. What kind of manuring is most suitable for 
 leguminous crops ? For garden crops, for orchards, and lawns ? 
 
 CHAPTER XII 
 
 295. What is the object of rotating crops? 296. Should the 
 whole farm undergo the same rotation system? 297. What is 
 meant by soil exhaustion? 298. What are the important princi- 
 ples to be observed in a rotation? 299. Explain why it is 
 essential that deep- and shallow-rooted crops should alternate? 
 300. Why is it necessary that humus be considered in a rota- 
 tion? 301. What is the object of growing crops of dissimilar feed- 
 ing habits? 302. How may crop residues be used to the best 
 advantage? 303. How is decline of soil nitrogen prevented by 
 a good rotation of crops? 304. In what ways do different 
 crops and their cultivation influence the mechanical condition 
 of the soil? 305. How may the best use be made of the soil 
 water? 306. How may a rotation make an even distribution of 
 farm labor ? 307. How are manures used to the best advantage in 
 a rotation? 308. In what other ways are rotations advantageous? 
 
 309. What may be said regarding long- and short-course rotations? 
 
 310. How is the conservation of fertility best secured ? 311. Why 
 does the use made of crops influence fertility? 312. What are the 
 essential points to be observed in the two systems of farming com- 
 pared in Section 344? 313. Is it essential that all elements re- 
 moved in crops be returned to the soil in exactly the amounts 
 contained in the crops? Why? 314. How does manure influence 
 the inert matter of the soil? 315. What general systems of 
 farming best conserve fertility? 316. Under what conditions 
 may farms be gaining in reserve fertihty? 317. Why in continued 
 
 z 
 
338 SOILS AND FERTILIZERS 
 
 grain culture does the loss of nitrogen from a soil exceed the 
 amount removed in the crop? Will a crop rotation alone maintain 
 the fertility of the soil ? 
 
 CHAPTER XIII 
 
 318. Why do soils need further treatment than plowing for the 
 preparation of the seed bed? 319. Why should different soils receive 
 different methods of treatment in the preparation of the seed bed? 
 320. How would you determine the best treatment to give a soil for 
 the preparation of the seed bed? 321. How do different methods of 
 plowing influence the condition of the seed bed? 322. Why does 
 complete inversion of sod frequently form a poor seed bed? 323. 
 How should the plowing be done to form a good seed bed? 324. 
 Why is it economy to pulverize the soil as much as possible when 
 it is plowed? 325. What effect does the moisture content of the 
 soil at the time of plowing have upon the condition of the seed 
 bed? 326. What effect does an excess of moisture have upon the 
 plowing and working of clay soils? 327. In what condition should 
 the seed bed be left as to fineness? 328. What is gained by fining 
 and moderately firming the seed bed? 329. Why is aeration of 
 the soil necessary? 330. Why do different soils require different 
 degrees of aeration? 331. Under what conditions can the seed 
 bed be prepared without plowing? 332. On what kinds of soil is 
 such a practice not advisable? 333. When is it advisable to mix 
 the subsoil with the surface soil? 334. When is it not desirable 
 to mix the surface soil and subsoil? 335. How can the plowing 
 and cultivation of the soil best be carried on to destroy weeds? 
 336. In what way does cultivation influence bacterial action in the 
 soil? 337. What classes of compounds in the soil are subject to 
 bacterial action? 338. How does the action of bacteria affect the 
 supply of available plant food? 339. What is meant by inocu- 
 lation of soils? 340. In what two ways can this be accomplished? 
 341. What soils are most improved by inoculation? 342. What 
 soils are least in need of inoculation ? 347. What other treatment 
 must often be combined with inoculation? 344. Why do different 
 
1 REVIEW QUESTIONS 339 
 
 crops require different cultivation? 345. How can the best kind of 
 cultivation for a crop be determined? 346. How can soils best be 
 cultivated to prevent washing and gullying? 347, What treatment 
 should such soils receive to be permanently improved? 348. What 
 relationship exists between bacterial diseases of soils and of crops ? 
 349. What treatment should soils receive to prevent bacterial 
 diseases? 350. How can the spreading of bacterial diseases 
 through infected seed be prevented? 351. Why must the sanitary 
 condition of a soil be considered? 352. What are the effects of some 
 forms of fungi upon soils? 353. In what way does thick or thin 
 seeding affect plant growth? 354. What effect does abnormal 
 crowding of plants have upon growth? 355. How would you deter- 
 mine the amount of seed for crop production? 356. How would 
 you determine the most suitable crop for any soil ? 357. What should 
 be the aim in selecting crops for soils? 358. Why should the crop 
 selected vary with diiferent types of soil? 359. What is the in- 
 herent fertility of soils? 360. What is the cumulative fertility of 
 soils? 361. How can the total fertility of soils be best increased? 
 362. Describe soils of the highest fertility. 363. Why must the 
 amount of plant food as well as the physical condition of the soil be 
 considered in the improvement of soils? 364. What relation does 
 the fertility of the soil bear to any agricultural system ? 
 
REFERENCES 
 
 1. Venable : History of Chemistry. 
 
 2. Gilbert: Inaugural Lecture, University of Oxford. 
 
 3. LiEBiG : Chemistry in Its Applications to Agriculture and 
 
 Physiology. 
 
 4. Gilbert : The Scientific Principles of Agriculture (Lecture). 
 
 5. Snyder: Minnesota Agricultural Experiment Station Bulletin 
 , No. 30. 
 
 6. Wiley : Agricultural Analysis, Vol. I. 
 
 7. Hilgard : Soils. 
 
 8. Maryland Agricultural Experiment Station Bulletin No. 21. 
 
 9. Snyder : Minnesota Agricultural Experiment Station Bulletin 
 
 No. 41. 
 
 10. Osborne : Journal of Analytical Chemistry, Vol. II, Part 3. 
 
 11. Bureau of Soils. Numerous bulletins on soil types. 
 
 12. Hellriegel : Calculated from Beitrage zu den Naturwissen- 
 
 schaft Grandlagen des Ackerbaus. 
 
 13. King : Wisconsin Agricultural Experiment Station Report, 
 
 1889. 
 
 14. Unpublished results of author. 
 
 15. King : Soils. 
 
 16. Roberts: Fertility of the Land. 
 
 17. Stockbridge : Rocks and Soils. 
 
 18. Snyder: Minnesota Agricultural Experiment Station Bulletin 
 
 No. 53. 
 
 19. Whitney : Division of Soils, U. S. Department of Agriculture 
 
 Bulletin No. 6. 
 
 20. Merrill : Rocks, Rock-weathering, and Soils. 
 
 340 
 
REFERENCES 34 I 
 
 21. MuNTZ : Comptes Rendus de rAcademie des Sciences, CX 
 
 (1890). 
 
 22. Storer : Agriculture, Vol. I. 
 
 23. Dyer : Journal of the Chemical Society, March, 1894. 
 
 24. Goss : Association of Official Agricultural Chemists Report, 
 
 1896 ; also Snyder : Minnesota Experiment Station Bulletin 
 No. 102. 
 
 25. Peter : Association of Official Agricultural Chemists Report, 
 
 1895 ; also Journal Analytical and Applied Chemistry, Vol. 
 VII, No. 6. 
 
 26. Loughridge : American Journal of Science, Vol. VII (1874). 
 
 27. HiLGARD : Year-book U. S. Department of Agriculture, 1895. 
 
 28. Houston : Indiana Agricultural Experiment Station Bulletin 
 
 No. 46. 
 
 29. Mulder : From Mayer ; Lehrbuch der Agrikulturchemie, 2. 
 
 30. Wheeler : Rhode Island Agricultural Experiment Station 
 
 Reports, 1892, 1893, etc. 
 
 31. Year-book U. S. Department Agriculture, 1895. 
 
 32. Loughridge : South Carolina Agricultural Experiment Station 
 
 Second Annual Report. 
 
 33. Association of Official Agricultural Chemists Report, 1893. 
 
 34 Washington Agricultural Experiment Station Bulletin No. 13. 
 
 35. Association of Official Agricultural Chemists Report, 1894. 
 
 36. California Agricultural Experiment Station Report, 1890. 
 
 37. Snyder : Minnesota Agricultural Experiment Station Bulletin 
 
 No. 29. 
 
 38. Snyder : Minnesota Agricultural Experiment Station Bulletin 
 
 No. 47. 
 
 39. Lawes and Gilbert : Experiments on Vegetation, Vol. I. 
 
 40. BoussiNGAULT : Agronomic, Tome I. 
 
 41. Atwater : American Chemical Journal, Vol. VI, No. 8, and 
 
 Vol. VIII, No. 5. 
 
 42. Hellriegel : Welche StickstofFe Quellen stehen der Pflanze 
 
 zu Gebote ? 
 
342 SOILS AND FERTILIZERS 
 
 43. Snyder : Minnesota Agricultural Experiment Station Bulletin 
 
 No. 34. 
 
 44. Warington : U. S. Department of Agriculture, Office of Ex- 
 
 periment Stations Bulletin No. 8. 
 
 45. HiLGARD : Association of Official Agricultural Chemists Re- 
 
 port, 1895. 
 
 46. Marchal : Journal of the Chemical Society (abstract), June, 
 
 1894. 
 
 47. KiJNNEMANN : Die Landwirthschaftlichen Versuchs-Stationen, 
 
 50 (1898). 
 
 48. Adametz : Abstract, Biedermann's Centralblatt fiir Agrikultur- 
 
 chemie, 1887. 
 
 49. Atwater : American Chemical Journal, Vol. IX (1887). 
 
 50. Stutzer : Biedermann's Centralblatt fiir Agrikulturchemie,i883. 
 
 51. Jenkins : Connecticut State Agricultural Experiment Station 
 
 Report, 1893. 
 
 52. Bulletin 107, U. S. Department of Agriculture, Bureau of Chem- 
 
 istry, Official Methods. 
 
 53. Journal of the Royal Agricultural Society, 1850. 
 
 54. From Sachsse : Lehrbuch der Agrikulturchemie. 
 
 55. Lawes and Gilbert : Experiments with Animals. 
 
 56. Beal : U. S. Department of Agriculture, Farmers' Bulletin 
 
 No. 21. 
 
 57. Snyder : Minnesota Agricultural Experiment Station Bulletin 
 
 No. 26. 
 
 58. Mainly from Armsby : Pennsylvania Agricultural Experiment 
 
 Station Report, 1890. Figures for grains calculated from 
 original data. 
 
 59. Heiden : Dungelehre.i 
 
 60. LiEBiG : Natural Laws of Husbandry. 
 
 61. Cornell University Agricultural Experiment Station Bulletins 
 
 Nos. 13, 27, and 56. 
 
 62. KiNNARD : From Manures and Manuring by Aikman. 
 
 63. Wyatt : Phosphates of America. 
 
t 
 
 REFERENCES 343 
 
 64. Wiley : Agricultural Analysis, Vol. III. 
 
 65. GoESSMANN : Massachusetts Agricultural Experiment Station 
 
 Report, 1894. 
 
 66. Connecticut (State) Agricultural Experiment Station Bulletin 
 
 No. 103. 
 
 67. GoESSMANN : Massachusetts Agricultural Experiment Station 
 
 Report, i8g6. 
 
 68. LiPMAN AND VooRHEES : U. S. Department of Agriculture, 
 
 Office of Experiment Stations Bulletin 194. 
 
 69. BoussiNGAULT : From Stoker : Agriculture. 
 
 70. Handbook of Experiment Station Work. 
 
 71. New York (State) Agricultural Experiment Station Bulletin 
 
 No. 108. 
 
 72. Voorhees : U. S. Department of Agriculture, Farmers' Bulle- 
 
 tin No. 44. 
 
 73. LiEBiG : Die Chemie in ihrer Anwendung auf Agrikultur und 
 
 Physiologic. 
 
 74. Warington : Chemistry of the Farm. 
 
 75. Lawes and Gilbert : Growth of Wheat. 
 
 76. Lawes and Gilbert : Growth of Barley. 
 
 ']']. Lugger : Minnesota Agricultural Experiment Station Bulle- 
 tin No. 13. 
 
 78. Lawes and Gilbert : Growth of Potatoes. 
 
 79. Snyder : Minnesota Agricultural Experiment Station Bulletin 
 
 No. 56. 
 
 80. Shaw : U. S. Department of Agriculture, Farmers' Bulletin 
 
 No. II. 
 
 81. White : U. S. Department of Agriculture, Farmers' Bulletin 
 
 No. 48. 
 
 82. Lawes and Gilbert : Permanent Meadows. 
 
 83. Thompson, Porteus : Graduating Essay, Minnesota School of 
 
 Agriculture. 
 
 84. Nefedor : Abstract, Experiment Station Record, Vol. X, 
 
 No. 4. 
 
344 SOILS AND FERTILIZERS 
 
 85. Snyder : Minnesota Agricultural Experiment Station Bulletin 
 
 No. 89. 
 
 86. Conn : Agricultural Bacteriology. 
 
 87. New York Agricultural Experiment Station Bulletins Nos. 
 
 270, 282. 
 
 88. Meyer : Outlines of Theoretical Chemistry. 
 
 89. VoORHEES : Fertilizers. 
 
 90. Cornell University Experiment Station Bulletin No. 103. 
 
 91. FRAPS : Annual Report 1904, Association Official Agricultural 
 
 Chemists. 
 
 92. Illinois Experiment Station Bulletin No. 93. 
 
 93. Canadian Experiment Farms Report, 1903, etc. 
 
 94. D. Land. Vers. Stat., 1899, 52. 
 
 95. A. D. Hall : The Soil. 
 
 96. Snyder: Minnesota Experiment Station Bulletin No. 109. 
 
 97. King : Investigations in Soil Management. 
 
 98. Ohio Agricultural Experiment Station Bulletin No. no. 
 
INDEX 
 
 Absorbents, i6o. 
 
 Absorption, of heat by soils, 47; of 
 
 gases by soils, 320. 
 Absorptive power of soils, 47, 51. 
 Acid phosphate, preparation of, 323. 
 Acids in plant roots, 258. 
 Acid soils, 1 01. 
 
 Acid soluble matter of soils, 81, 320. 
 Aeration of soils, 275. 
 Aerobic ferments, 177. 
 Agricultural geology, 54. 
 Agronomy, 9. 
 Air and soil formation, 60. 
 Air movement through soils, 314. 
 Albite, 65. 
 Alchemy, i. 
 Alkaline soils, 96. 
 Alkali soils, improving, 99. 
 Aluminum of soils, 78. 
 Amendments, soils, 233. 
 Ammonium compounds, 130. 
 Ammonium sulphate, 155. 
 Anaerobic ferments, 177. 
 Analysis of soils, how made, 87; 
 
 value of, 88, 90; interpretation of, 
 
 91-92. 
 Apatite rock, 67. 
 Apparatus, list of, 308. 
 Application, of fertilizer, 252; of 
 
 manures, 181, 184. 
 Arrangement of soil particles, 18. 
 Ashes, 218; action of, on soils, 219; 
 
 testing of, 324. 
 Assimilation, of nitrogen, 116; of 
 
 phosphates, 199. 
 Atmospheric nitrogen, n8. 
 Atwater, 122, 151. 
 
 Availability of plant food, 92. 
 Available nitrogen, 128, 152. 
 Available phosphate, 203, 210. 
 
 Bacterial action and cultivation, 138, 
 
 298. 
 Barley, fertilizers for, 253; food 
 
 requirements of, 261. 
 Blood, dried, 147. 
 Bone, dissolved, 208; steamed, 208; 
 
 fertilizers, 207. 
 Bone ash, 208. 
 Bone black, 209. 
 Boussingault, 11, 119, 120. 
 Buckwheat, food requirements of, 266. 
 
 Calcium as essential element, 223. 
 
 Calcium carbonate, and nitrification, 
 140; compounds of soils, 79; ni- 
 trate and cyanamid, 156; phos- 
 phate, 68. 
 
 Capillarity, 30; and cultivation, 36. 
 
 Capillary water, determination of, 
 312. 
 
 Carbon, of soil, 74; sources for plant 
 growth, 74. 
 
 Cavendish, 2. 
 
 Cereal crops, 259. 
 
 Chemical composition of soils, 71. 
 
 Chlorine of soil, 75. 
 
 Citric acid, use of, in soil analysis, 84. 
 
 Classification, of soils, scheme for, 
 326; of elements, 71. 
 
 Clay, formation of, 67; particles, 16; 
 sedimentation of, 317. 
 
 Clover, as manure, 154; nitrogen 
 
 345 
 
346 
 
 INDEX 
 
 returned by, 122, 134, 289; root 
 nodules, 125; manuring of, 269. 
 
 Coal ashes, 220. 
 
 Color, of plants, influenced by nitro- 
 gen, 118; of soils, 47, 50; and soil 
 temperature, 314. 
 
 Combination of elements in soils, 72. 
 
 Commercial fertilizers, 233, 254; 
 abuse of, 245; and tillage, 244; 
 and farm manures, 254; compo- 
 sition of, 234; extent of use, 233; 
 field tests with, 248; for special 
 crops, 253; home mixing of, 243; 
 inspection of, 237; judicious use 
 of, 246; mechanical condition of, 
 238; misleading statements, 241; 
 nitrogen of, 238; phosphoric acid 
 of, 239; plant food in, 237; potash 
 of, 240; preparation of, 234; 
 valuation of, 241 ; variable com- 
 position, 234. 
 
 Composition, of soils, 95, 97, 98; of 
 manures, 1 59. 
 
 Composting manures, 178. 
 
 Corn, fertilizers for, 254; food re- 
 quirements of, 263; and manure, 
 185; soils, 23. 
 
 Cotton, fertilizers for, 267. 
 
 Cottonseed meal, 151. 
 
 Cow manure, 170. 
 
 Crop residue, 275. 
 
 Cultivation, after rains, 38; and bac- 
 terial action, 298; shallow surface, 
 37; and soil moisture, 313; and 
 soil temperature, 49. 
 
 Cumulative fertility, 304. 
 
 Cyanamid, 156. 
 
 Davy, work of, 3. 
 
 Deficiency, of nitrogen, 249; of 
 phosphoric acid, 250; of potash, 
 250; of two elements, 250. 
 
 Denitrification, 141. 
 
 De Saussure, work of, 3, 118. 
 
 Dilute mineral acids, action of, 84. 
 
 Diseases of soils, 301. 
 Dissolved bone, 208. 
 Distribution of soils, 62. 
 Drainage, 34, 47, 300. 
 Dried blood, 147. 
 
 Early truck soUs, 22. 
 Earthworms, 61. 
 Electricity of soU, 52. 
 Evaporation, 53; heat required for, 
 
 46. 
 Excessive use of fertilizers, 252. 
 Experimental plots, 248. 
 Experiments, 310, 325. 
 Exposure and soil temperature, 49. 
 
 Fallow fields, 145. 
 
 Fall plowing, 41. 
 
 Farm manures, 158, 189; and com- 
 mercial fertilizers, 254. 
 
 Feldspar, 64, 237. 
 
 Fermentation of manures, 177. 
 
 Fertility, conservation of, 285; im- 
 portance of, 305 ; removed in 
 crops, 254. 
 
 Fertilizers, amount to use, 252; in- 
 fluence upon soil water, 44; on 
 barley, 253; on wheat, 253. 
 
 Field tests with fertilizers, 248. 
 
 Fine earth, 14. 
 
 Fish fertilizer, 151. 
 
 Fixation, 191; of ammonia, 194; of 
 phosphates, 192; of potash, 192; 
 due to zeolites, 191; nitrates not 
 fixed, 193; and available plant 
 food, 194. 
 
 Flax, food requirements of, 264; soils, 
 
 24- 
 
 Flesh meal, 1 50. 
 
 Forest fires, in. 
 
 Formation of soils, 54, 62. 
 
 Form of soil particles, 17. 
 
 Fruit soils, 23. 
 
 Fruit trees, fertilizers for, 270. 
 
INDEX 
 
 347 
 
 Gains, of humxis, 114; of nitrogen, 
 
 133- 
 Garden crops, fertilizers for, 269. 
 Geological study of soil, value of, 69. 
 Gilbert, 7. 
 
 Glaciers, action of, 57. 
 Grain soils, 24. 
 Granite, 66. 
 
 Grass lands, fertilizers for, 268. 
 Grass soils, 24. 
 Guano, 207. 
 Gullying of soils, 300. 
 Gypsum and manure, 179. 
 
 Hair, 152. 
 
 Hay land, fertilizing, 268. 
 
 Heat, and crop growth, 50; pro- 
 duced by manures, 178; of soil, 46, 
 50; required for evaporation, 46. 
 
 Heiden, 174, 180. 
 
 Hellriegel, 22, 28, 123. 
 
 Hen manure, 172. 
 
 Hog manure, 172. 
 
 Hops, fertilizers for, 267. 
 
 Hornblende, 65. 
 
 Horse manure, 1 70. 
 
 Human excrements, 174. 
 
 Humates, 103; as plant food, 107. 
 
 Humic acid, 112. 
 
 Humic phosphates, 105, 210. 
 
 Humification, 104. 
 
 Humus, 103; active and inactive, 114; 
 causes fixation, 192; composition 
 of, 106; extraction of, trom soils, 
 321; loss of, from soils, 11 1; soils 
 in need of, 113. 
 
 Hydrogen, compounds of soil, 77. 
 
 Hydroscopic moisture, 32; deter- 
 mination of, 310. 
 
 Importance of field trials, 251. 
 Income and outgo of fertility, 286, 290. 
 Infected seed and soU diseases, 301. 
 Inherent fertility, 304. 
 Injury of coarse manures, 46, 182. 
 
 Inoculation of soUs, 143. 
 Insoluble matters of soils, 82. 
 Iron compounds of soil, 80. 
 
 Jenkins, 152. 
 
 Kainit, 179, 216, 243. 
 Kaolin, 67. 
 King, 37, 40, 41. 
 
 Laboratory note- book, 307; practice, 
 
 308, 326. 
 Lawes and Gilbert, 6, 121, 122, 260. 
 Lawn fertilizers, 272. 
 Leached ashes, 219. 
 Leaching of manure, 175. 
 Leather, 152. 
 Leguminous crops, fertilizers for, 
 
 269; as manure, 154; nitrogen 
 
 assimilations of, 122, 125. 
 Liebig, 5, 6, 174, 257. 
 Lime, action on soils, 225; amount 
 
 of, in soils, 224; amount removed 
 
 in crops, 224; excessive use of, 229; 
 
 fertilizers, 225; indirect action of, 
 
 227; physical action of, 228; 
 
 stone, 68; use of, 229; lime and 
 
 acid soil, 226; and clover, 226. 
 Liquid manure, 164. 
 Loam soils, 27. 
 Loss, of fertility in grain farming, 287; 
 
 of humus, hi; of nitrogen, 132, 
 
 145- 
 Losses from manures, 176-177. 
 
 Magnesium compounds of soils, 79. 
 
 Magnesium salts as fertilizers, 230. 
 
 Mangels, fertilizers for, 254. 
 
 Manure, from cow, 170; hen, 172; 
 hog, 172; horse, 170; sheep, 171. 
 
 Manures, farm, 158; composition of, 
 159; composting of, 178; crop 
 producing value, 168; direct ap- 
 plication of, 181; fermentation of, 
 177; influence of, on soil tempera- 
 
348 
 
 INDEX 
 
 ture, 313; on moisture, 313; in- 
 fluenced by foods, 162; influenced 
 by age and kind of animal, 1 6g ; 
 leaching of, 175; liquid, 164; 
 mixing of, 173; solid, 164; and 
 soil water, 45, 112; and tempera- 
 ture, 48; preservation of, 175; 
 use of, 181, 184; use of, in rotation, 
 278; value of, 189; volatile prod- 
 ucts from, 173. 
 
 Manurial value of foods, 167. 
 
 Manuring, of crops, 185; pasture 
 land, 183. 
 
 Marl, 228. 
 
 Mechanical, analysis of soils, 19; 
 condition of fertilizers, 238; compo- 
 sition of soil types, 27. 
 
 Methods of farming, influence of, 
 upon fertility, 114. 
 
 Mica, 66. 
 
 Micro-organisms and soil formation, 
 54, 60. 
 
 Mineral matter and humus, 109. 
 
 Mixing manures, 173. 
 
 Moisture for nitrification, 139. 
 
 Movement of water after rains, 39. 
 
 Muck, 153, 161. 
 
 Mulching, 42. 
 
 Nitrate of soda, 154. 
 
 Nitric nitrogen, 154.' 
 
 Nitrification, 135; conditions neces- 
 sary for, 136; elements essential 
 for, 140; and plowing, 145; and 
 sunlight, 139. 
 
 Nitrogen, assimilation, 118, 121; of 
 clover plant, 122, 125; as plant 
 food, 116; compounds of soil, 76; 
 compounds, solubility of, 323; 
 deficiency of, in soil, 249; gain of, 
 in soils, 133-134; loss of, by 
 fallowing, 144; losses of, from soil, 
 132; ratio of, to carbon, 131; re- 
 moved in crops, 128; in com- 
 mercial fertilizers, 238; in rain 
 
 water and snow, 131; amount of, 
 
 in soUs, 128; in organic forms, 127; 
 
 as nitrates, 129; as nitrites, 129; 
 
 availability of, 127; forms of, 126; 
 
 origin of, 126. 
 Nitrogenous manures, 146, 157. 
 Number of soil particles, 19. 
 
 Oats, food requirements of, 262. 
 
 Odor of soils, 51. 
 
 Organic acids, action of, upon soils, 
 84, 85. 
 
 Organic compounds of soil, classifi- 
 cation of, 103; source of, 102. 
 
 Organic nitrogen, 147, 152. 
 
 Organisms, ammonia- producing, 141; 
 of soil, 141; nitrous acid, 140; 
 nitrifying, 137; products of, 142. 
 
 Orthoclase, 65. 
 
 Osborne, 20. 
 
 Oxidation of soil, 48. 
 
 Oxygen compounds of soil, 77. 
 
 Oxygen, necessary for nitrification, 138. 
 
 Pasteur, 8. 
 
 Peat, 153, 161. 
 
 Percolation, 32. 
 
 Permanent meadows, manuring of, 
 268. 
 
 Permeability of soils, 44. 
 
 Phosphate fertilizers, 198; commer- 
 cial forms, 201 ; manufacture of, 
 204; as plant food, 198; removed 
 by crops, 199; reverted, 202; 
 rock, 203; slag, 206; use of, 205. 
 
 Phosphoric acid, of commercial fer- 
 tilizers, 201, 239; available, 198, 
 203, 210; acid in soils, 200; defi- 
 ciency of, 250; removal in crops, 
 199; soluble and insoluble in soils, 
 84; testing for, 323; value of, 205. 
 
 Phosphorus compounds of soils, 75. 
 
 Physical, analysis of soils, 316. 
 
 Plant food, classes of, 80; ash and 
 fertilizers, 256; distribution of, 93, 
 
INDEX 
 
 349 
 
 94; in soil solution, 8r, 196; total 
 and available, 92, 93. 
 
 Plants, crowding of, in seed bed, 302. 
 
 Plowing, depth of, 43; energy re- 
 quired for, 293; fall, 41; spring 
 41; influence of, on soU, 291; in- 
 fluence of, on moisture, 294; influ- 
 ences nitrification, 291. 
 
 Pore space, 13. 
 
 Potash fertilizers, 212; use of, 222; 
 of commercial fertilizers, 240; salts, 
 218. 
 
 Potash, in soils, amount of, 214; 
 sources of, 215; soluble and in- 
 soluble, 84; and lime, joint use of, 
 222; muriate of, 217; sulphate, 
 217; removed in crops, 213. 
 
 Potassium compounds of soil, 78. 
 
 Potato, fertilizers for, 264; food 
 requirements of, 264; soils, 22. 
 
 Preliminary trials with fertilizers, 248. 
 
 Priestley, 2. 
 
 Property of soils, 1 2 ; modified by 
 farming, 115. 
 
 Pulverized lime rock, 227. 
 
 Pulverizing soils, 295. 
 
 Quartz, 64. 
 Questions, 327. 
 
 Rainfall and crop production, 29. 
 Rape, food requirements of, 266. 
 Reaction of soils, determination of, 
 
 319- 
 
 References, 340, 344. 
 
 Relation of crop and soil type, 303. 
 
 Reverted phosphoric acid, 202. 
 
 Review questions, 327. 
 
 Roberts, 43, 175, 293. 
 
 Rock disintegration, 55, 68. 
 
 Rocks, composition of, 64, 69; prop- 
 erties of, 318. 
 
 Rolling of soils, 40, 294. 
 
 Root crops, fertilizers for, 266. 
 
 Roots, action on soil, 255, 276. 
 
 Rotation, and soil water, 277; and 
 weeds, 280. 
 
 Rotation of crops, 273, 284; prin- 
 ciples involved, 274; length of, 281 ; 
 problems, 284; and farm labor, 
 278; and humus, 275; and insects, 
 280; and soil nitrogen, 276. 
 
 Salt as a fertilizer, 229. 
 
 Sand, grades of, 14, 15. 
 
 Schlosing, 8. 
 
 Schubler, 5. 
 
 Seaweeds as fertilizers, 231. 
 
 Sedentary soils, 62. 
 
 Seed, amount of, per acre, 303. 
 
 Seed bed, preparation of, 291. 
 
 Seed residues, 151. 
 
 Sheep manure, 171. 
 
 Silicon and silicates, 74. 
 
 Silt particles, 17. 
 
 Size of soil particles, 14. 
 
 Skeleton of soils, 14. 
 
 Small fruits, fertilizers for, 271. 
 
 Small manure piles, 183. 
 
 Sodium compounds of soils, 80. 
 
 Sodium nitrate, 154. 
 
 Soil, composition of, 97, 98; con- 
 servation of fertility, 285; ex- 
 haustion, 274, 304; management, 
 303; particles, study of, 319; sam- 
 pling of, 86, 87; solution of, 80, 196; 
 types, 21. 
 
 Soils and agriculture, relation of, 305 ; 
 crops suitable for, 303. 
 
 Soot, 230. 
 
 Specific gravity of soil, 13. 
 
 Specific heat of soil, 48. 
 
 Sprengel, s._ 
 
 Spring plowing, 41. 
 
 Stassfurt salts, 216. 
 
 Stock farming and fertility, 288, 
 
 Storer, 75, 148. 
 
 Strand's plant ash, 231. 
 
 Street sweepings, 232. 
 
 Stutzer, 152. 
 
350 
 
 INDEX 
 
 Subsoiling, 40. 
 
 Sugar beets, and farm manures, 185; 
 
 fertilizers for, 265. 
 Sugar beet soils, 24. 
 Sulphate of potash, 217. 
 Sulphur compounds of soil, 75. 
 Superphosphates, 204. 
 Surface subsoil, mixing of, 297. 
 
 Tankage, 149. 
 
 Taste of soils, 51. 
 
 Temperature of soils, 46. 
 
 Testing for nitrates, 322. 
 
 Tests with fertilizers, 248. 
 
 Thaer, work of, 3. 
 
 Tobacco, manuring of, 186. 
 
 Tobacco stems, 221. 
 
 Transported soils, 62. 
 
 Truck farming and fertilizers, 269. 
 
 Tull, 8. 
 
 Turnips, fertilizers for, 254, 266. 
 
 Van Helmont, i. 
 
 Vegetation and soil formation, 61. 
 
 Ville, 121. 
 
 Volatilization of ammonium salts, 322. 
 
 Volcanic soils, 64. 
 
 Volume of soils, 13. 
 
 Voorhees, 243, 269. 
 
 Warington, 8, 139. 
 
 Washing of land, 300. 
 
 Water, action of, upon rocks and 
 soils, 56; in rock decay, 59; bot- 
 tom, 29; capillary, 30; capillary 
 conservation of, 36-38. 
 
 Water holding, capacity of soils, 311; 
 hydroscopic, 32; losses by evapo- 
 ration, 23'> losses by percolation, 
 32; losses by transpiration, 34; of 
 soil, 29, 34; of soil influenced by 
 drainage, 34; by forest regions, 35; 
 by manures, 45; by mulching, 42; 
 by plowing, 41; by rolling, 40; 
 by subsoiling, 40; required by 
 crops, 28; soluble matter of soils, 
 196. 
 
 Weeds, cultivation to destroy, 297; 
 fertility in, 231. 
 
 Weight of soils, 12; how determined, 
 
 313- 
 Wheat, fertilizers for, 253; food 
 
 requirements of, 260; soils, 25-26. 
 Whitney, 19, 52. 
 Wilfarth, 124. 
 
 Wind as agent in soil formation, 62. 
 Winogradsky, 8. 
 Wood ashes, 218. 
 Wool waste, 152, 231. 
 
 Zeolites, 67, 191. 
 
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 64-66 FIFTH AVENUE, NEW YOEK 
 
JUN 33 1908 
 
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