> 1 THE UNIVERSITY OF ILLINOIS LIBRARY 630.7 II6b co p A8RIGULTURAL U1BARY Agricultural Experiment Station BULLETIN No. 225 NITRATE PRODUCTION IN FIELD SOILS IN ILLINOIS BY ALBERT L. WHITING AND WARREN R. SCHOONOVER URBANA, ILLINOIS, MARCH, 1920 CONTENTS OF BULLETIN No. 225 PAGE INTRODUCTION 21 Purpose of Investigation 23 Effect of Soil Treatment on Amount of Nitrate Produced 24 Influence of Tillage on Nitrate Production 24 The Course of Nitrate Production in Field Soils 25 Interpretation of Experimental Eesults 27 NITRATE PRODUCTION IN CORN-BELT SOILS (NORTH FARM AT URBANA) 29 Nitrate Nitrogen in Soil Growing Corn in 1915, Series 400 30 Nitrate Nitrogen in Soil Growing Corn in 1916, Series 500 32 Value of Active Organic Matter in Nitrate Production 35 Gain for Phosphorus 36 Gain for Limestone 36 Nitrate Nitrogen in Soil Growing Corn in 1917, Series 200 36 Nitrate Nitrogen in Soil Growing Corn in 1918, Series 300 38 Nitrate Nitrogen in Soil Growing Wheat in 1915-16, Series 200 40 Nitrate Nitrogen in Soil Growing Oats in 1917, Series 500 43 SOME IMPORTANT FACTS SHOWN BY DATA FROM THE NORTH FARM 45 Corn Crop 45 Wheat Crop 46 Oat Crop 46 EFFECT OF SOIL TREATMENT AND OF CROPPING SYSTEMS ON NITRATE PRODUCTION (SOUTH FARM AT URBANA) 47 Influence of Green Manure as Compared with Stabile Manure 49 Influence of Kaw Rock Phosphate 50 Effect of Limestone on Nitrate Production 53 Cropping Systems as Influencing Nitrate Production 54 Crop Sequence as Influencing Nitrate Production 55 Moisture Determinations on the South Farm 56 SOME IMPORTANT FACTS SHOWN BY DATA FROM THE SOUTH FARM 59 CONCLUSIONS 60 APPENDIX (Methods) 62 NITRATE PRODUCTION IN FIELD SOILS IN ILLINOIS BY ALBEET L. WHITING, CHIEF IN SOIL BIOLOGY, AND WARKEN E. SCHOONOVEE, 1 ASSOCIATE IN SOIL FERTILITY INTRODUCTION The ability of a soil to produce ample nitrate nitrogen to meet the requirements of all growing crops, except legumes, and to ac- complish this in spite of the natural losses which are caused by rainfall, is a most important factor in economical and maximum food production, The value of systematic nitrate studies of field soils is conceded since nitrogen is accepted as an essential plant-food element. It is further emphasized by the fundamental fact that nitrate nitrogen is the form of nitrogen utilized by all non-leguminous plants. If the supply is deficient at any period during which the plant requires it r then it is a limiting factor in crop yields. The production of a bushel of corn is dependant upon many factors, any one of which .may cause failure if operating adversely. Nitrates may be present in unlim- ited quantities, but the largest yields may not accrue from such a condition if phosphorus, or calcium, or water, or some other factor, is lacking. It is an important duty of the soil biologist to find meth- ods by which the crop demands for nitrate nitrogen will be amply met by the soil at all times. This publication offers information to that end. There are three main factors which exert favorable influences upon the production of nitrates in field soils. The first factor is soil treatment, such as the application of organic matter, limestone, and phosphorus; the second is tillage operations, such as ploAving, cultivating, fallowing, and mulching; and the third, climatic condi- tions temperature, moisture, and aeration. In dealing with these three factors it is obviously more important for the farmer to direct his at- tention to soil treatment, which he can control, than to the climatic factors, which can be only slightly controlled by farm operations. In- fluences produced by tillage operations are under his control, and therefore tillage practices should receive, in conjunction with soil treatment, most careful attention. 'Mr. Schoonover, formerly First Assistant in Soil Biology, was responsible for the chemical analyses during the years 1915, 1916 and 1917, before enlisting in lie Sanitary Corps of the United States Army. 21 22 BULLETIN No. 225 [March, There are a few definite negative factors which decrease the supply of nitrates in soil. These are, the crop grown (including weeds), rainfall, utilization of nitrate by bacteria, molds, algae, and other forms of plant life, and denitrification, a process which, how- ever, has not been found to be important in normal soils. The crop, of course, is not a factor in studies of fallow soils. Of all the positive factors, the organic matter in the form of green manures, farm manures, and crop residues is the most impor- tant, and attention to it will produce the greatest increase in nitrate production because it .is the source of nitrogen from which the nitrate is manufactured. Other kinds of soil treatment, such as the appli- cation of limestone or of rock phosphate, exert a very great in- fluence on nitrate production when a base is lacking to neutralize acid and when calcium is needed as a food, or when phosphorus is deficient either for the plant or for the bacteria. These two positive factors are both easily controlled and are direct in their action. While it is true that temperature controls the course of nitrate production, the total amount and rate at which it is produced, which are the vital considerations, are functions of the organic matter, of limestone and phosphorus, and of tillage operations. It is well known that all plants and animals, people included, require more food at certain periods in their development than at others. Inasmuch as all crops except legumes obtain their nitrogen in the form of nitrate, 1 from the soil, it will not be out of place to expand the first statement of the introduction: At those stages when the crop demands a large amount of nitrate, there should be a large reserve in the soil, or at least the soil should possess the ability to meet the crop requirements, however large they may be. If this is accomplished, then nitrogen ceases to limit crop production. If a large nitrate reserve is built up ahead of consumption by the crop, the critical period is likely to be passed without the slowing down of crop growth or the delaying of maturity. Further, with a large reserve the later demands made upon the soil by the growing crop are much more easily met by a normal rate of nitrate pro- duction. A knowledge of the amount of nitrate present in Illinois soils un- der various kinds of soil treatment is especially desirable at this time. *No evidence has been found to support the view that ammouia is directly assimilated by farm crops in these soils. Ammonia determinations were made on many samples of these soils which afforded excellent comparisons with the nitrates. However, the results have no practical significance. The results were consistently around 5 to 12 pounds per acre except where large applications of stable manure had been made. Aeration with magnesium oxid was used to de- termine the ammonia. NITROGEN PRODUCTION IN FIELD SOILS IN ILLINOIS 23 The acute situation in which many eastern and southern farmers find themselves on account of the high cost of commercial nitrogen and the failure to take advantage of the nitrate production which is possible on the farm, suggests the significance of such a study of Illinois soils. Chili saltpeter, or sodium nitrate, the cheapest source of com- mercial nitrogen available in large amounts, had reached a figure be- fore the war which brought the cost of nitrogen to 18 to 20 cents per pound. In 1918 the federal government controlled the supply of so- dium nitrate in this country and sold it to the farmers at $75.50 per ton, cash at the seaboard. Nitrogen in this form cost in Illinois approx- imately 27 cents per pound at the railroad station. As a food emergency measure one would not question using this nitrogen, even at a higher cost, on the poorer lands of the eastern and southern states; but continued reliance upon it under peace conditions, for growing staple crops, is indicative of faulty soil science and of a failure to utilize our unlimited natural farm resources. PURPOSE OF INVESTIGATION The investigations reported herein were undertaken in order to systematically measure the amount and rate of nitrate production in certain surface soils of Illinois, principally with respect to the influence exerted by seasonal changes, soil treatment, different crops, and rainfall. Answers to the following questions have been gained by the data obtained : 1. What influence may proper soil treatment exert on the amount and rate of nitrate production in Illinois soils ? 2. Will the nitrogen of a green-manure crop plowed under in the spring be available to the succeeding crop of that year, and how does it compare with stable manure in the rate at which it will produce nitrate for the succeeding crop ? 3. How do different cropping systems affect the amount of nitrate produced? 4. At what time of year does the maximum production of nitrates occur? 5. What are the relative rates of nitrate production during the four seasons of the year? 6. Which of the farm practices observed tends to decrease the loss of nitrate which occurs as a result of leaching? 7. What are the periods of greatest nitrogen utilization by the corn crop ? 24 BULLETIN No. 225 [March, EFFECT OF SOIL TREATMENT ON AMOUNT OF NITRATE PRODUCED Soil treatment exerts the greatest influence upon the amount of nitrate produced. In an earlier paragraph the importance of organic matter was mentioned. It can hardly be emphasized enough, as will be seen by a study of the data herein presented, for the largest increase in nitrate production is derived from applications of organic matter. Limestone causes increases in nitrates even on poor soils, but it is easily seen that continued liming, without applications of organic matter, would lead to crop failure because of a deficiency of nitrogen out of which to make nitrate. The application of limestone for legumes and the plowing under of legumes bring about both direct and indirect increases in nitrates. It has been shown in earlier work at this station that tricalcium phosphate furnishes the base calcium for nitrate formation and, at the same time, phosphorus is made soluble. 1 Crop residues, stable manures, and green manures, with natural phosphates, added to the soil, effect not only the liberation of the phosphorus and potassium from the soil, thereby meeting the requirements of large crop yields, but they also produce an increased accumulation of nitrates. In the proper use of these three substances organic matter, limestone, and phosphorus lies the way of solving the problem of sufficient nitrate production for all crops. If these are given intel- ligent attention, along with tillage operations, then the farmer will have left nothing undone on his part to insure a sufficient nitrate supply. INFLUENCE OF TILLAGE ON NITRATE PRODUCTION Experiments on the influence of plowing, cultivating, mulching, and fallowing, in their direct and indirect effect upon nitrate pro- duction, have been reported from Rothamsted in England, from Samara in Russia, and from the Wisconsin, Kansas, New York (Cornell), and Illinois agricultural experiment stations. Certain facts are outstanding in these results and a brief consideration of them is pertinent: Plowing increases nitrate production. Cultivation conserves nitrates by preventing weeds from using part of the available supply. Mulching reduces loss by rapid leaching and conserves moisture, thereby tending to maintain the nitrate supply in the soil. Fallow- ing enables the soil to accumulate large amounts of nitrates because none are removed by a growing crop. 1 See Bui. 190, Soil Bacteria and Phosphates, 111. Agr. Exp. Sta. 1916. NITROGEN PRODUCTION IN FIELD SOILS IN ILLINOIS 25 Plowing is an essential farm operation for the production of most crops. Even tho it had no beneficial influence in connection with the maintaining of fertility, it would have to be carried out for other purposes, such as the preparation of the seed bed. Its relation to nitrate production is this: In plowing, the whole zone in which the nitrates are produced is mixed and aerated, and a large amount of nitrate-producing material is thereby often incorporated in the well- aerated soil. The whole nitrate-producing zone is in no way sealed up. Early plowing compared with late, and spring plowing compared with fall, as influencing nitrate production under satisfactory experi- mental conditions, have not been studied for humid regions. Kesults from five years' determinations at Samara, Russia, altho obtained in the semiarid region, demonstrated the value of fall and early spring plowing over later plowing, as in May and June. In Kansas, plowing in July was superior to August, August was superior to September, and September was superior to October, for winter wheat. Unless a green manure is to be plowed under just before seeding wheat, the land should be plowed early in the summer after the removal of the crop. In following this method, moisture and nitrates are con- served and nitrate production encouraged. In some seasons these effects may be considerable. Where a crop of green clover is plowed under, rapid decomposition results and early plowing is not so essen- tial from the standpoint of nitrate production. The data regarding cultivation as a means of increasing nitrates are very conflicting. If, however, cultivation is considered to be for the purpose of killing weeds, then it is not necessary to emphasize its value as a means of conserving nitrates for the crop. If weeds are not a consideration, then the problem becomes different. The effect produced by cultivation is undoubtedly related to soil conditions. The late Professor King expressed the belief that the cultivation of a wet soil was detrimental because of the sealing up of the nitrate- producing areas. It must be understood, however, that cultivation is not to be compared with plowing, for cultivation stirs only the surface soil and seldom disturbs the most important nitrate-producing zone. The opinion is even held by some that cultivation does not add air to a soil. If cultivation is to be practiced for any purposes, including the killing of weeds, it should certainly be shallow in order not to injure the crop. THE COURSE OF NITRATE PRODUCTION IN FIELD SOILS - * That climatic factors influence nitrate production in soils has already been stated. The results obtained in various parts of the world are in agreement as to the effect exerted by increasing temper- atures in spring and early summer. Since the production of nitrates is the result of a series of biochemical reactions, production is increased 26 BULLETIN No. 225 [March, in a manner similar to most chemical reactions by a rise in temper- ature. The actual course of nitrate production in Illinois is as follows : During the winter no nitrate is produced, because of low tem- peratures, and none is lost while the soil is frozen ; b'ut as soon as the soil thaws, if heavy rains occur, a loss of nitrate results. With the rising temperature .of early spring the ammonifying and nitrifying organisms multiply, and a gradual increase in nitrate production sets in usually in March or early April. Cold, wet periods often retard nitrate production at this time of the year, and rains are rather dis- astrous if many occur in a short period. In the month of May, when there is usually a marked rise in temperature, nitrate production increases rapidly, especially during the latter part of the month. In June optimum temperature and moisture conditions are approached. The greatest rate of production and the largest accumulation of nitrates consequently occur in this month, especially is this true of soils plowed in May or under preparation for cultivated crops that are to be planted in May or June. However, winter wheat, oats, clovers, alfalfa, or other crops on the land in March or April may so affect con- ditions that the largest accumulation does not appear in June, but in May. These crops protect the soil from excessive losses and use the largest amount of nitrate in late May and early June. Immediately after their removal nitrate production falls to a low ebb, usually owing to excessive dryness. In a wet summer, nitrates are produced in relatively large amounts during July and August, but usually with the coming of midsummer, the combination of temperature and moisture conditions is such as to cause a very great reduction of nitrate production in most soils in this climate. Land in corn shows a marked decrease in nitrates after the crop is laid by and no tendency in normal summers to recover the same efficiency which it displays in June. Even in the case of land on which wheat and oats have been cut, little nitrate production occurs when the two months of July and August are considered as a whole. Showers at this time often cause an increase, but no continuous ten- dency toward large production has been observed. In fallow soils nitrate formation increases during these months, but at a slower rate than during May and June. A second rise in nitrate production always occurs in September, October, and sometimes November. Temperature and moisture conditions seem to approach a second optimum in those months, altho the increase in late summer and fall is not usually so great as in late spring and early summer. Production ceases with the approach of winter. The course of nitrate production is not widely different for nor- mal seasons, but it does change with moist summers, when nitrates are likely to be produced in larger amounts than in a normal summer, 1920] NITROGEN PRODUCTION IN FIELD SOILS IN ILLINOIS 27 and with open, mild winters, when the losses are greater than in winters of normal temperature. INTERPRETATION OF EXPERIMENTAL EESULTS In presenting the results which follow it has been found advisable to report the actual pounds per acre of nitrogen as nitrate, at the various dates of sampling. Each figure is an average of two deter- minations, each determination being that of a field sample consisting of twelve to fifteen cores, according to the crop and plot. The plots on the North Farm are one-tenth acre each and those on the South Farm, one-fifth acre each. The method of presenting the results permits a study of the extent of the fluctuations, and when the rainfall is noted, together with the kind of crop grown, the causes of such fluctuations are apparent. This is important, for the belief has been expressed that nitrates were extremely liable to fluctuations which rendered their determination of no value. The fact is the exact opposite. Definite causes for all the fluctuations are very accurately and easily found if the fluctuations are only studied thoroly. It is perfectly evident that if only sporadic attempts at determining nitrates are made, unreliable conclusions will result. In examining the results one must not overlook the influence of the crop. As an illustration, Plots 501 and 510 of the Davenport series may be used. Plot 501 is a poor producer of nitrate compared with Plot 510. If however, some element other than nitrogen is lim- iting crop growth on Plot 501, then even when corn, for example, is at the period of greatest growth, a large surplus of nitrate may be found. On the same date Plot 510, supporting a larger growth, may show less nitrate than Plot 501. But the fact that Plot 510 is a better nitrate-producing plot will be shown by its record of two or three weeks before or a week or more later. It may even happen that the best plot will show consistently less accumulation than some other plots, and in such case the crop yield, or still better, a determination made without the presence of a crop, will assist in indicating the true condition. It is difficult, however, in some cases to measure all the nitrate produced, for the reason that a catch crop grown for green manure will reduce the nitrate temporarily, altho it will greatly in- crease it when later plowed under. In the course of a rotation these effects are all considered and their true results measured. * Limestone increases nitrate production but it also greatly benefits legumes, which may take up the extra nitrate produced at certain times ; and it therefore becomes difficult always to determine immedi- ately the exact effect of one factor in a series of combinations. When no crop occupies the land, a comparison of the effects of given treat- ments is much easier to obtain. 28 BULLETIN No. 225 [March, The presence of nitrate in soil growing a crop, combined with a study of various treatments, nevertheless serves to answer the question whether the soil is ahead of the nitrate needs of the /rop. A method of ascertaining the nitrate-producing ability of the soil when an analysis of the field samples shows no surplus will be described later. All the results included in this bulletin are expressed in pounds of the element nitrogen in the form of nitrate, per acre of surface soil (the soil from about to 6% inches in. depth). Fourteen pounds of nitrogen are equivalent to 62 pounds of nitrate radicle (NO 3 ), or 85 pounds when reported as pure sodium nitrate (NaN0 3 ) or pure " Chilisaltpeter. " The figures reported are averages of duplicate field samples in all cases, unless otherwise indicated, and in some cases they represent averages of four, eight, and sixteen determinations. The column headed "Apparent utilization of nitrogen," must be understood to represent the minimum utilization of nitrogen, for no method was used by which it could be exactly determined how much nitrate may have been produced and used during each period. It is possible to show therefore, as nitrate utilization, only the amount of decrease between an earlier and a later date. A more exact figure could be obtained by making analysis of the crops, but that was not possible in these long-continued experiments. How- ever, as these figures are comparative they do not represent as great fluctuations from the actual as might at first appear, especially is this true of determinations made during a normal season and about the critical period for corn (June 25 to July 15) because, owing to de- creased rainfall and increased temperature, there is a rapid falling off in nitrate production at that time. It is evident that where pro- duction had ceased the figures would approach a high degree of ac- curacy. Moisture determinations are included in all cases, as they are important in nitrate studies and, further, have a value in showing the relation between climatic conditions and the actual moisture content of these field soils. The figures given show the number of tons of water accompanying two million pounds of water-free soil. Certain facts connected with these determinations will be indicated elsewhere. 1980] NITROGEN PRODUCTION IN FIELD SOILS IN ILLINOIS 29 NITRATE PRODUCTION IN CORN-BELT SOILS The first studies included in this report were conducted in 1915 on certain plots of the Davenport series on the North Farm, at Urbana. 1 On these five series a rotation is practiced consisting of wheat, corn, oats, and clover, with a fifth field in alfalfa for five years, after which it is rotated with the other four crops while the alfalfa is grown on another of the series for five years. This rotation has been prac- ticed since 1911, and the reader is referred to Illinois soil reports for earlier and more detailed information regarding these series. A few brief statements are necessary here to explain the soil treatment on the plots listed below, which were selected for study. In the beginning the six, plots selected were : 1 No treatment (except a rotation of crops) 2 Residues 3 Manure 4 Eesidues, limestone 6 Eesidues, limestone, phosphorus 10 Manure, limestone, phosphorus On the residues plots the corn stalks are left standing and the wheat and oat straws returned, as are also clover hullings and, in the main, all legumes except alfalfa and the legume seeds. Catch crops of sweet clover or mixtures of clovers are seeded in- the wheat on the residues plots and on the plots receiving extra heavy treatment (No. 10 of each series), and are plowed under in the following spring for corn. A catch crop has been seeded in the corn but has not been suc- cessful. The manure plots receive applications of farm manure in amounts corresponding to what could be made from the crops pro- duced, and all residues and grains are removed. The manure is ap- plied in the fall or winter, for the corn crop, and is plowed under. Limestone is applied at the rate of two tons per acre every four years and at the rate of two and one-half tons per acre for the alfalfa once in five years. The application is made ahead of the wheat and is disked in. Bone meal has been applied on the east half of each series, at the rate of 800 pounds per acre, once in four years ; and raw rock phosphate, has been applied on the west half at the rate of 2,400 pounds per acre, once in four years. The phosphate is applied ahead of the corn, it being plowed under with the manure and residues. No attempt was made to study the influence of each form of phosphorus on nitrate production. J See appendix for method of determining nitrates, used in these investigations. 30 BULLETIN No. 225 [March, NITRATE NITROGEN IN SOIL GROWING CORN IN 1915 SERIES 400, UNIVERSITY NORTH FARM Series 400 on the North Farm at Urbana was 'the first series studied. This series had grown' wheat in 1914, and the wheat straw, manure, and phosphates were applied and plowed under in the fall. Corn was planted in 1915 in the usual manner. The first samples for nitrate determination were taken on June 17. The corn was laid by about July 1. Table 1 shows the amounts of nitrate nitrogen found on the dates of sampling. The apparent amount disappearing between June 28 and July 15, or 17 days during the rapid growth of crop, is shown in the sixth column. It should be stated that the rainfall was high during this season, 5.17 inches occurring in 28 days and 3.85 inches during the seventeen-day period chosen. 1 The distribution of the rainfall was such that it appeared not to reduce the supply of nitrate, and the re- duction found is therefore assigned to that taken up by the corn crop. Observations on the growth of the corn were in accordance with the rapid use of nitrate recorded. The yields of corn are given in the last column for comparison with the amount of nitrate nitrogen used during this seventeen-day period. While there is a direct relationship between the amount of nitrate present and crop yielcj, it does not always appear, for, as earlier stated, other factors may be operating to limit crop produc- tion when nitrates are plentiful. The two manure plots were apparently using the nitrate earlier than the others: Plot 403, receiving manure alone, shows a decrease of 10 pounds from June 17 to June 28, which added to the apparent utilization from June 28 to July 15 makes a total of 26.5 pounds, or the same amount as determined for the plot receiving residues, lime- stone, and phosphorus, (No. 406), with identical crop yields. The manure is known to decompose faster than the straws of small grains. It sometimes contains urea, which is rapidly converted into nitrate under favorable conditions; and certain other compounds in manure are transformed faster than the nitrogen of straws. The manure shows its true relationship here, as both manure and residues were applied at the same time. Plot 410, receiving the extra-heavy manure treatment (where manure is applied in quantity five times the usual amount), along with phosphorus and limestone, did not show five times as much nitrate on June 17 as that found on the plot receiving manure alone (No. 403), but only 1.26 times as much ; but on June 28 it still contained about 20 pounds more than Plot 403. The nitrogen appears to be in great ir rhe rainfall data reported in this bulletin were obtained from records of the soil physics division of the Agronomy Department. NITROGEN PRODUCTION IN FIELD SOILS IN ILLINOIS 31 TABLE 1. NITRATE NITROGEN IN SOIL GROWING CORN IN 1915: SERIES 400, UNIVERSITY NORTH FARM Pounds per acre in 2 million, pounds of surface soil (about to 6J3 inches), water-free basis Plot Treatment Date of sampling Apparent utilization of nitrogen in 17 days Corn yield, bu. June 17 June 28 July 15 401 402 403 404 406 410 None (except crop rota- tion) 32.8 32.2 45.1 32.5 33.3 56.8 31.7 32.6 35.0 33.9 31.2 54.5 27.6 19.7 18.5 12.3 6.8 15.4 4.1 12.9 16.5 21.6 25.4 39.0 66.4 66.8 80.8 73.2 80.8 82.0 Residues Manure Residues, lime Residues, lime, phosphate. Manure-x, lime, phos- phate-x TABLE 2. MOISTURE CONTENT OF THE SOIL GROWING CORN IN 1915: SERIES 400, UNIVERSITY NORTH FARM Tons of water with 2 million pounds of surface soil (about to & 2 /z inches), water-free basis 1 Pint I )ate of sampling p Treatment June 17 June 28 July 15 401 None 244.6 241.5 251.5 402 R 243 266.1 248.4 403 M 237 3 237.6 240.7 404 RL 240.7 232.3 251.6 406 RLP 246.1 239.9 255.7 410 MxLPx 241 .4 246.9 264.4 J It is a simple matter to change tons of water per acre to equivalent inches of rainfall by dividing the tons per acre by 113.25, which is the weight in tons of an acre-inch of water. By moving the decimal point in any of the figures in these moisture tables one place to the left, the percentage of water, as expressed on an arbitrary water-free basis, is obtained. The percentage of moisture on the field basis is obtained by adding 1000 to any figure, dividing the original figure by that sum, and then pointing off two places. excess on this plot, and was not used economically for grain produc- tion. These results do not indicate that nitrate nitrogen was limiting crop production, at least as late as July 15, with crops of this magni- tude, for the check plot on that date still contained 27.6 pounds, having used apparently only 4.1 pounds in the seventeen-day period, and Plot 410, which had apparently used about ten times the amount used on the check plot, still contained 15.4 pounds. The corn on Plot 410 grew much faster than on the check, but not six times as fast. The highest yielding plots produced more stalks, and these are undoubtedly richer in nitrogen, which condition disturbs the normal ratio between nitro- gen assimilated and yield of grain. The residues-limestone-phos- phorus plot (No. 406), with the lowest nitrate-nitrogen content on June 28, appears to have had the better balance of plant-food elements, and here the nitrate nitrogen was more economically used. 32 BULLETIN No. 225 . [March, It is difficult to conceive how an application of a nitrogenous fer- tilizer, even if it contained nitrate nitrogen, could have been of any value on these plots when the corn was laid by, for the lowest nitrate content still unused in the surface soil of any plot was the equivalent of 40.8 pounds of sodium nitrate, or 200 pounds of 3.4-percent nitrog- enous fertilizer. NITRATE NITROGEN IN SOIL GROWING CORN IN 1916 SERIES 500, UNIVERSITY NORTH FARM Alfalfa was seeded on this series in 1911 but failed and was re- seeded in 1912. Hay crops were removed from all plots during 1912, 1913, 1914, and 1915. The stubble was plowed under in March, 1916, together with manure and phosphate, and the limestone applied in May. The results of determinations for nitrate nitrogen are found in Table 3. The high content of nitrate nitrogen is important to ob- serve: the alfalfa stubble appears to be easily decomposed and must be rich in nitrogen. The presence of a crop of this kind on the land also assists in preventing losses from leaching by taking up large amounts of available nitrogen and by preventing the rapid downward flow of water. Even on the plot receiving no treatment the produc- tion of nitrate nitrogen is shown to have been high and it was probably much higher on all plots than it would have been if hot dry winds had not injured the pollen at the time of fertilization and by reducing crop yields reduced the utilization of nitrate nitrogen. There is an increase shown on all plots, from April 4 to June 5, except on Plot 510. The decrease on Plot 510 between May 11 and June 5 is related to the rapid growth of the crop, which is always evident here and which is also evident at times on Plot 6 of each series at a much earlier period than on the other plots. A decrease is noted on all plots from June 5 to June 26. The high moisture content from June 5 to June 26, with 3.44 inches of rainfall well distributed over the period, so slowed down nitrate production that consumption by the plant became greater than production, and a consequent reduction in nitrate is seen to have taken place. The increase which followed in the next period was due to the reduced moisture content furnishing more favorable conditions as regards oxygen supply. The temperature from August 11 to August 23 was an important factor in rapid increase, as it appears to have been at the optimum, while during the preceding period it was too high when coupled with the dryness of the soil. From August 23 to September 14 all plots except Nos. 504 and 510 lost nitrates. This loss is traceable to a rainfall of 1.48 inches on 1920} NITROGEN PRODUCTION IN FIELD SOILS IN ILLINOIS 33 OCOCO^OO <3i > Os 1> CO OS CO l> CO CO * CO* CN il. ll ^OiO^cO?- ir COCN CM CN CN"* 3 <; o IO rH rjc IO lO * PH W Q CO COCO-* CO 1 * H .2 it CM OOOSOSO I! ^^ l>t^COCMCN CO s ^ CM CO O OS 1> rH * H o* OO O >O CO-* S ' OrH I s - CM 00 CD >O CD 0} 8"| C?^ COrHCM rHrH CO o _g M OrH CD-* CM O H PJ ^ IO rH CO >O OO i-H IOCOO OCO CD & S M rH Tfl O OS COCO - ^ g ^^ IO rH CD 00 * CD to co co co * * rH , a A bb t- CO Tt< * OS rH h- I a a OH ^ rHOCO OS t^ * rS S >, OSIOIOO5 * CD i 2 "S CO M O ^^ >O OS rH OS I> GO *H O o O CM CO GO OS 7 * ^^ rH rH OS rH GO IO IO CO * CO IO OS 1. P4 CO OOCDrH O rH-* S * COlO t^ * GO 1 ^ CO rH OS-* CM * ^^ CO CN CO rH CO IO CO CM CN CO CN * , K |i 3 1 p< .' ! PH 1-5 ^o llil H *? fc I g P ^ S CO o co os -a 55 s 1 DH K O " SO J>O CO IO CO O 0) CO Q CO CO-*-* 00 CN GO OS 00 GO OO t^ CN CN CM CN CN CN t> rH COO CO CO OS OCDCN * OS-* CM CN CM CN CM CN lOO OS CM CN * co-* coos * os CO IOCO * IOCN CM CM CM CM CNCN GO GO OS IOCO O &^ * O3l>-* rH OS OS OS 00 OS OOO rH rH rH rH CM rH O * OS OS GO CN S^co ^J *-^ ^ IO CO CO l~*- rH * CNCNrH rHCM rH CO -*1>CO CO t^ 1- CO GO 00 00 GO CD rHU3GOCNt^CN t^ CD CO CD OS CN CN CM CN CM CO CN OH ^ O OS 00 rH CM CO i *-9 CO OSCOOl^CN IO * * IO CO IO o +-) oj N CO "5 CO CO COCN w S rH 1-9 OOOOcDGOGOt^ CD IOCO CO IO * 300 IO CO OS CN IO CO O O OS i 1 OS OS CN CN rH CM rHrH COrHCOCN !>* 3 co r-S *i>iot^eoco * COCO CO COCO CN CNCN CNCN CM CD CO 00 CM 00 OS CO Ceo 3CN r-S [> i^ co co co os CN CNCN CNCN CN a> 00-*COI^OSO ^ r^co * co co co MCN CNCN CNCN ^ t^CO CO rH CN CO o3 ^^ O CD OS O rH OS CO 10 * IO O CO CN CM CM CNCN CM CM OS OS CO * O *rHCO-* CNCO OS OS OS OS OS OS CN CN CN CN CN CM > -u ^ 1 0) a o 'Jda3 _O ^.' rHCM CO-* COO r> o oo o rH 34 BULLETIN No. 225 [March, September 6. Up to September 14, the plots had increased in mois- ture content 75.2 tons per acre, and a further increase of 89.8 tons appeared by December 6. Under these conditions one might have ex- pected an increase in nitrate content, but it is necessary to study the periods separately in order to realize the true relationship of nitrate production to rainfall. In the period from September 14 to October 30, there was 3.17 inches of rainfall, which by being concentrated greatly reduced the amount of nitrate in the soil. The moisture content on October 30 was 243.4 tons, antf. on November 20, 246.2 tons; under these conditions some plots had gained nitrate. By reference to the rainfall records, one finds only .78 inches of precipitation in the twenty-one days. Here again the rainfall was not sufficient to cause a loss of nitrate but instead stimulated its production. A gain this late in the season is important, as winter wheat would often benefit by the nitrate pro- duced. From November 20 to December 6 the average moisture con- tent increased from 246.2 tons to 284.3 tons owing to a rainfall of 1.64 inches. However, as the rainfall was concentrated a loss of nitrates resulted. Attention is called to the number of determinations showing a nitrate-nitrogen content of more than 35 pounds per acre which are recorded for this series in this year even tho the series carried the corn crop. Seventy-eight of the 90 figures reported are above 35 pounds per acre. On the same series in 1917 (see Table 12) only six determinations out of 48 were above 35 pounds.. The difference in this case is probably related to the initial decomposition of the alfalfa roots, and to the different conditions under which the soil was placed by be- ing planted to crops which grow at widely different times. (It will be noted that oats were grown in 1917). When a crop is planted in May and does not begin to take up much nitrate until about the middle or last of June, the soil is given ample opportunity to build up a large reserve of nitrate (if it possesses the active nitrogen), and it will meet the demands of a rapidly growing crop. On the other hand, with an early seeded crop and one which more completely covers the ground, such as oats, the accumulation during April, May, and June is not so great as where the land is fallow, since the crop is constantly draw- ing on the nitrate supply and has materially reduced it before the period of greatest accumulation is approached. A study of the figures for Plot 510 shows the relative rate at which nitrate was being taken up by the corn crop during certain of APPARENT. NITRATE CONSUMPTION ON PLOT 510, 1916 Period Days Pounds taken up June 5 to June 26 21 11.0 June 26 to July 3 7 6.0 July 3 to July 8 5 45.7 1920] NITEOGEN PRODUCTION IN FIELD SOILS IN ILLINOIS 35 the periods. The large use of nitrate on these plots during a relatively few days is in agreement with the results reported for the corn crop of 1915 on Series 400 ; it was earlier than observed in some of the other seasons. All the plots in Series 500 decreased materially in nitrate- nitrogen content from July 3 to July 14. On Plots 506 and 510 the lowest figures came before July 8, but on the 'other plots not until July 14. A slight gain occurred between July 14 and July 21. A decrease then occurred to August 11, which indicates that production had practically ceased. An increase is then noted to August 23. With an average moisture content of but 153.2 tons on July 21 and only 128 tons on August 2, and with nitrates disappearing, a rainfall of .79 inches on August 11 raised the moisture content to 178.2 tons and was responsible for the increase of the nitrate nitro- gen that followed, the average increase for the series being 20.9 pounds during the twelve-day period. The moisture content had rapidly fallen from July 8, when it was 202.6 tons, to August 2, when it was only 128 tons. The figures indicate that a moisture content of 130 to about 150 tons was not sufficient for nitrate production at this time of year. An increase in nitrate was found when the moisture content was 178 tons and even as the content decreased to 150 tons. The amounts of nitrate shown in Table 3 as removed in eleven days, considered in connection with the crop yields, illustrate the fact that the exact relationship between the amount of nitrate removed and crop yields cannot be ascertained on account of the presence of some of the many other factors which may influence the yields. It must be admitted, nevertheless, that nitrate was present in this series in large amount, even after the crop had taken up more than it needed to produce the yields obtained. Value of Active Organic Matter in Nitrate Production If the results for the entire season from Plot 502 are compared with those from Plot 501, it will be found that Plot 502 (residues) produced 53.7 pounds more nitrate nitrogen than Plot 501 (no treat- ment). This difference is due to the effect of the decomposing crop residues which are returned to the soil, and to the larger growth of roots. The manure plot (No. 503) was 13.2 pounds superior to the plot receiving no treatment (No. 501) in the production of nitrate nitrogen, when allowance is made for the nitrogen difference in crop yields on the basis of the standard values for nitrogen in corn ; while the resi- dues plot was 39.1 pounds superior to the manure plot. 36 BULLETIN No. 225 [March, Gain for Phosphorus The residues-limestone-phosphorus plot shows ^ gain of 8.1 pounds over the residues-limestone plot, as the average for the season. This plot yielded 6.6 bushels more corn, which is estimated to have contained 9.9 pounds of nitrogen. Figured in this manner, we have 18 pounds more of nitrate nitrogen produced where the phosphorus was applied. Gain for Limestone A comparison of the residues-limestone plot with the residues plot shows that 12.1 pounds more nitrate nitrogen was available in the former plot than in the latter, while limestone produced 1.8 bushels more corn, which makes a gain attributable to limestone of 14.8 pounds. NITRATE NITROGEN IN SOIL GROWING CORN IN 1917 SERIES 200, UNIVERSITY NORTH FARM This series grew soybeans in 1915 and wheat in 1916. A catch crop of sweet clover was seeded in the wheat in February, 1916, on the residue plots and on Plot 210. The sweet clover made an excel- lent growth in the spring of 1917. In March the manure and phos- phates were applied. The land was plowed on May 3 and the corn planted May 14. In Table 5 are given the results obtained. It will be noted that an increase in nitrate production occurred on four plots up to July 7, when the usual tendency to decrease was manifest, and as noted in 1915 and 1916 the richest plot in this series (No. 210) showed the decrease at the earliest date. Spring rains were not very disastrous. There was only 5.73 inches of rain from March 15 to May 19. Losses of nitrate are apparent on Plot 201, which had no green-manure crop, and on Plot 202, which had but little protection as the green-manure crop was very poor. The heavy rainfall in the period from May 19 to June 18 was so scattered and the moisture content of the soil was such that only slight losses were evident. During the remainder of the season the rain was not sufficient to cause a loss until in October, when a decrease is seen. Very interesting differences in the color and the height of the corn on the residues plots as compared with the manure plots de- veloped early in July thruout the series. Results bearing on the value of sweet clover, which was the cause of the differences observed, for nitrate production, are reported for the 1918 corn crop. Attention should be directed to the much slower growth of the corn this year NITROGEN PRODUCTION IN FIELD SOILS IN ILLINOIS 37 SO -1 03 "* a vjo. te o B , co 2 1^ rH -tJ OS fS rH O Si B3 O o s O o CO fc 3 H O (M O BS H H n h-t frj 15 1 P-rJ OOOTMO^OO 31 -0 OS CO CO CO CO CO CO t^COOOOSO 1 1 -u a fl.O g s? CO 00 rH -* |> TH CC" ^^ Ovrt 2 CO CD i-lt> CO CO 00 10 d .s -X O^WOTHN a lOCO lOOO COlO 1 1 CO rH >O CO O CO F COOrHCO rHCO rH i-H rH l-H CO CO ^ CO t 1 1 Tt* l>- 3rH O CO O rH O OS -9 O CO 00 OS CO rH CO CO rH CO CO CO bC a t>CO 1C rH OOCO a S i c 10 3CO >-5 CO CO rHCO CO * OOO Ot> CO "o3 Q Coo 3rH OSOt^OcOO i 1 CO i-H CO CO ^ . OOOOOOCO OS 03 OS t> rH ICOOOOS CO CO (M rH CO CO , cous^^ooo o3O OOCO rH IO O CO rH rH i 1 T 1 CO l>rH 00 OOOrH ^ rH I-H rtn O * O CO (M rH rH rH CO O5 CO O rH 00 * B.O O O >O O CO * ^ . CO O l> CO rH CO S- CO-* CO OOS CO rH rH i 1 rH i s fl 03 a gj A " ^1 3 . . . 0_| H- J ~c E rH CO CO M* CO O O O O O O rH o -a * I >< 4 I! B CO O O O M O a r t O I'* 00 C<1 00 t^- 00 CO "So 0^ t^ O i-H * 00 CO co co co i> 10 1^- IOIC c rt U3 1C Tf< (N 1^ lO CO CO >-. TtHO Tt* 1C i-H 00 ^"^ 3i-H i- O i-( 00 OO Tt< O5 CO CO l-l 1-1 O rH (N CO CO CO CN| (M >, 1C i-H CO 00 l> CO 3> >-s 00 CO i-H i-l CO * co i^- 1>- 1-- co os COCO COCO CO C^J bC a CO OS t>t> Ol> "a S 03 fl 10 3 O CO CO CO CO COCO (4-1 o O 1> 00 COCO OrH (B i n floo 3i-i 1-5 OO CO OS CO 00 OS l^ OS IO-00 "O O CO (N COCO COCO a ^ rH -* 00 CO CO 00 CO * CO CO t^ CO CO t^ Ol^ CO OO CO CO CO CO CO CO >> OOOOO CO COCO 030 S" co os * co os i i OOOOOOO100O COCO COCO CO CO * CO OS OS CO TH 4- CO COO O rH CO OCOOrHrH rH CO COCO CO CO CO COiOOSOS(NCO 4 s CO rH CO OS CO 00 OS I-H Os O Os i i CO CO CO COCO CO OS 00 CO OS t^ CO rf"3 S" * TH O OS CO 1C co >o 10 coco >o CO COCO CO CO CO 4> d | 3 H x ::: 1 i UStf ^tf^tfrts -u O S rH CO CO^< COO OOOOOrH CO CO CO CO CO CO 38 BULLETIN No. 225 [March, compared with that of similar periods in previous years, as evidenced by the small amounts of nitrate removed in the twelve-day period at about the time the corn was laid by. NITRATE NITROGEN IN SOIL GROWING CORN IN 1918 SERIES 300, UNIVERSITY NORTH FARM This series was in wheat in 1917 ; sweet clover was seeded on the residues plots and also on Plot 310. The manure was applied during the winter, and both it and the sweet clover were plowed under at the same time. The growth of sweet clover was excellent. All ten plots were studied this year. As it had been found that samples taken a few weeks before, during, and a little after the critical periods of crop growth were a sufficient basis upon which to judge the nitrate pres- ent and the rate of accumulation for the crop, fewer samples were taken on this series than on the others. In Table 7 are presented important results showing the effect of sweet clover when plowed under green, upon nitrate production, and the differences between its effect and that of the stable manure which was applied to some of the plots of the series. Very notice- able differences in the color and height of the corn appeared in favor of the residues plots. (The sweet clover is grown in addition to the regular crop residues, and when plowed under young may contain 100 pounds of nitrogen per ton of dry matter, and probably even con- tains some nitrate at that stage.) A comparison of the figures for the residues plots and those for the manure plots demonstrates in a concise manner the superiority, this season, of the sweet clover over the manure for nitrate produc- tion. While there appears to be some tendency for the manure to reduce the differences later in the season, the reduction is not large. In 75 percent of the determinations the sweet clover proved to be superior to the manure, and where inferior, it was, except in one case, either during rapid growth of the crops or later, which surely detracts little from the value of the sweet-clover results. Only once did the normal manure plots reach 40 pounds, while the sweet-clover plots exceeded even this figure in twelve cases out of twenty-four. The ordinary run of manure, by the time it is applied to the soil, has lost a large part of its rapidly decomposing nitrogenous compounds, and the nitrate production resulting from its application should be ex- pected to be less rapid than that from a green manure. The increase found here, on a relatively good soil, from sweet clover, suggests what may be possible in the way of insuring the success of this legume thru applications of limestone and phosphorus. The plots which had made the largest growth of sweet clover were the plots receiving the best 1930} NITROGEN PRODUCTION IN FIELD SOILS IN ILLINOIS 39 TABLE 7. NITRATE NITROGEN IN SOIL GROWING CORN IN 1918: SERIES 300, UNIVERSITY NORTH FARM Pounds per acre in 2 million pounds of surface soil (about to water-free basis inches), Plot Treatment Date of sampling Apparent utilization of nitrogen in 7 days June 10 June 17 June 24 July 2 July 12 Aug. 2 301 302 303 304 305 None 22.9 22.7 26.6 62.0 28.9 34.8 52.6 32.6 66.3 33.0 30.2 47.8 38.0 48.9 33.0 28.2 26.0 22.2 16.8 15.9 30.3 40.0 29.9 20.7 15.6 26.8 29.3 21.1 19.3 27.9 2.0 21.8 15.8 32.1 17.1 R M RL ML 306 307 308 309 310 RLP 63.6 19.0 55.8 28.8 90.7 97.0 34.4 63.5 29.4 96.6 61.5 33.9 49.1 43.6 81.5 21.4 23.0 21.5 27.2 42.9 16.0 23.5 16.5 20.4 30.2 22.7 22.0 20. 16.2 20.8 40.1 10.9 27.6 16.4 38.6 MLP RLPK MLPK MxLPx TABLE 8. INCREASES OF NITRATE NITROGEN ON RESIDUES PLOTS (SWEET CLOVER) AS COMPARED WITH MANURE PLOTS, SOIL GROWING CORN IN 1918: SERIES 300, UNIVERSITY NORTH FARM Pounds of nitrogen per acre Plots com- pared Treatments Date of sampling June 10 June 17 June 24 July 2 July 12 Aug. 2 302:303 304:305 306:307 308:309 R over M -3.9 33.1 44.6 27.0 20.0 33.3 62.6 34.1 9.8 15.9 27.6 5.5 3.8 .9 -2.6 -5.7 10.1 5.1 -7.5 -3.9 8.2 -8.6 .7 3.8 RL over ML RLP over MLP RLPK over MLPK TABLE 9. MOISTURE CONTENT OP THE SOIL GROWING CORN IN 1918: SERIES 300, UNIVERSITY NORTH FARM Tons of water with 2 million pounds of surface soil (about to 6J3 inches), water-free basis Plot Treatment Date of sampling June 10 June 17 June 24 July 2 July 12 Aug. 2 301 302 303 304 305 None 224.4 242.7 246.4 263.8 268.8 222.4 230.9 240.0 245.5 257.8 220.1 237.6 225.0 253.9 256.0 351.8 357.7 387.9 284.0 324.4 224.2 239.3 243.8 251.7 262.3 138.1 149.4 145.2 157. f 151.3 R M RL ML 306 307 308 309 310 RLP.. 267.5 270.0 263.2 280.8 309.0 255.6 255.3 253.6 265.2 279.5 253.7 250.1 249.1 247.8 268.5 371.4 390.8 378.4 340.7 329.4 253.1 252.5 259.7 268.4 298.9 165.8 161.5 159.4 165.2 177.5 MLP RLPK MLPK MxLPx 40 BULLETIN No. 225 [March, soil treatment, such as residues, limestone, and phosphorus, and they also returned the highest nitrate production from the sweet clover. The residues plot shows rather large increases over the check plot in nitrate production, altho the amount of green material turned un- der was small compared with that on Plots 304, 306, 308, and 310. Limestone was responsible for some increases in nitrate in the early periods. Phosphorus in addition to residues and limestone is responsible for the maximum results. The results on Plot 310 are derived from a combination of manure and sweet clover and ho of course are not to be considered with these other comparisons. These figures show how soil treatment can influence the rate and amount of nitrate stored up for the critical period of a crop, and they lend further emphasis to statements on the first page of the intro- duction. Further investigation along these lines are very essential, as this particular study represents only one season, altho it does in- clude four comparisons. The nitrate removed in seven days is given in the ninth column of the table and demonstrates in a very clear manner the value of sweet clover in meeting the demands of rapidly growing crops. These figures coincide with those showing the rate of growth and the color of the crop observed during this period and later. It will be observed that both limestone and phosphorus on the residues plots were as- sociated with a large assimilation of nitrate during the seven-day period. The figures for the manure plots are much lower than for the residues plots ; it appears that the crop was using nitrate from the manure plots much more slowly and over a longer period. NITRATE NITROGEN IN SOIL GROWING WHEAT IN 1915-1916 SERIES 200, UNIVERSITY NORTH FARM A nitrate study of soil on which winter wheat is growing involves a set of conditions different from those present with crops such as corn, soybeans, or even oats. There must be a supply of nitrates for fall growth, and nitrate production must be rapid and early enough to satisfy the spring growth. Soil that is growing wheat can hardly be expected to accumulate a large reserve of nitrate, as happens in the case of soil in preparation for corn, because the wheat crop is drawing heavily on the supply that would otherwise accumulate dur- ing May and a part of June. It is therefore essential that the wheat be started with a plentiful supply of nitrate in the fall, and if this is done less loss will result from leaching, owing to the protection afforded by good plant growth, and more nitrate will be available to meet the critical period in spring. This can be accomplished if the total active organic matter of the soil is kept at a high figure. Plowing as early as possible is to be 1920] NITROGEN PRODUCTION IN FIELD SOILS IN ILLINOIS 41 recommended, especially if no green-manure crop is to be turned un- der, as it saves moisture and stores up nitrates. In most seasons the rainfall during July, August, and a part of September is not the cause of serious losses of nitrate. Soybeans were grown on this series in 1915 and were removed on September 22. Limestone was applied en September 29 and the wheat seeded September 30. This series, except Plot 210, gained in nitrate until November 23 in spite of the demands of the wheat. The fall rains were very small, and no losses of nitrate resulted. The lime- stone and residues plots appear to have started out with the larger amounts of nitrates. The results presented in Table 10 show that this series was effi- ciently supplying nitrates for the fall growth of the wheat and, at the same time, that the nitrate production in most cases actually increased ; it decreased only a very little ori Plot 210, where the larg- est growth occurred. It is difficult to tell whether a loss from rainfall occurred before March 18, but such would seem to be the case, as the total precipitation of the winter, December 9 to March 18, was only 9.93 inches. It is however, evident that the soil was able to meet the needs of the crop and even to gain rapidly up to May 4, after which time the demands of the crop materially reduced the amount of nitrate present. The large use of nitrate by the wheat crop occurred during the period May 4 to June 21. The true nitrate-producing capacity is shown in the period after the wheat had been removed and before the sweet clover had made scarcely any growth. The amounts of nitrate found on this series in August, September, and November indicate the value of residues, manure, limestone, and phosphorus, especially the latter, in increasing nitrate production. The effect of limestone, which was applied in 1915, is pronounced on certain plots on this series. The reason for manure assuming a higher value than residues is that, contrary to the general practice, a light application was made as a top-dressing on the wheat in the spring. In twenty-nine days (May 4 to June 2) only 14.5 pounds of nitrates were used on the check plot, 10.9 pounds on the residue plot, 16.7 pounds on the manure plot, 37 pounds on the residue-limestone plot, 2.7 pounds on the residue-limestone-phosphorus plot, and 3.0 pounds on the manure-limestone-phosphorus plot (extra-heavy treaf- ment). These are very small decreases compared with the amounts found for the corn the same year, in only eleven days. This serves to show that the wheat had taken up considerable nitrate in the fall and early spring, and was now taking it very gradually compared with a crop like corn. The amounts shown for Plots 206 and 210 mean very little, as the growth of the crop was apparently keeping the supply of nitrate rather low, while the other plots lacking in phos- phorus were not demanding so much. 42 BULLETIN No. 225 [March, o !N CO t^ CXI O CXI 10 CO CXI H 1^ OS I> 00 rH 00 CO i-H i-( i-H CO * i I-H 00 00 CO OS tn H CD^ l> OS O 1C rH ^H i-l CN (N (N CO CO 1 CO CO TjH OS Tfl CO 2; t-i 09 &~ COCOON j-4 CO r-(i-i CN (N iO CO s ^ 6/D/vi OTtHCO'-lOCO W 41 S ^^ TjH CO CO 1 CO OS rH rH i-H (N (N CO S v R i- f-J < tt a ^ITJ COIN OCO l> 00 diS O>o * coco co rt te 8 " g FH C sS i-s -> IOOOCOO(NCO H rt) w T 1 O a r-l CO i 1 CO OS O COCOCO-* *H * g S^ CO IN * TjH OS CO C CO co 1C CO -^ 1C CO r-l W 13 O " O o i 1 bl I N U3 l> i-H CM C OS I-H ^ S3 ft I 0(N S5 t^ OS OS CO CO CO CO V 1C * rH O OS rH -g !5 -? M 03 Si ! O I I O OS rH O O 00 "3 o a>co CO 00 CO CO 1C 1C * TJH rfH 00 00 O CO t>- 00 t-- N- O C (N OS !>- T-H CO CO O5 OO 00 CD-* I>CO COl> CO |2 OO CO CO 00 O OS *""' O OS * os * os bJD fl f3 (M CO OOO COrf (N CO -9 ::::?: i 1 1 i 1 (M (- O CO CO OS Q S rH 3 CO (M CXI d CM (N IN rj< 1> CM (N I> rjn 5^ Cd CO Tj< (N -H CO OS OS OS O O5 >O CN IM CM CO (N (N CO COCO (N CO O li aco ! i-l GO CO CO t^ Tf< l^COI>OOCOCO (N CN IN (N O CO CN| (N CXI CN CXI (N *c id * CO CO * CO os i i S" I N U3 O t^ CO O O3 t^oot^t^oo t^ N CXI CX| CXI CN CXI o irj co co i> i i os "cl 0 iO COt^l> o a> -^ 03 S* CO -*I^ COIN OS t>- t- CO CO CD 1-- (N (N ^S j : : : i : : :CLH ^ IdSrtrtS -t-2 o S i-l CXI CO Tf CD O OOOOOrH (N (N (N