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To renew call Telephone Center, 333-8400 UNIVERSITY OF ILLINOIS LIBRARY AT URBANA-CHAMPAIGN y L161 O-1096 SWEET CLOVER IN ILLINOIS CONTENTS DESCRIPTION OF PLANT P 211 SPECIES OF SWEET CLOVER. 214 Biennial White-Flowered Sweet Clover 215 Annual White-Flowered Sweet Clover 218 Biennial Yellow-Flowered Sweet Clovers 219 Annual Yellow- Flowered Sweet Clovers 220 Varieties for Illinois 220 CLIMATIC AND SOIL REQUIREMENTS OF SWEET CLOVER 221 Drainage is Beneficial But Not Essential 222 Sweet Clover Demands a Sweet Soil 223 Limestone Need Greater on Light-Colored Soils 226 Sweet Clover Responds to Phosphates 228 Potash Is Important on Many Soils 229 Manure Aids in Securing Stand 229 Inoculation Necessary for Success With Sweet Clover 230 SWEET CLOVER AS A SOIL BUILDER 231 Increased Crop Yields Follow Sweet Clover 232 Benefits From Sweet Clover Due to Combination of Factors 235 Phosphate Makes Sweet Clover a Better Soil Builder 239 Potash Frequently Improves Corn Yields After Sweet Clover 240 HANDLING THE SWEET-CLOVER CROP 241 Plow Sweet Clover Green Unless Needed for Pasture 241 Early Spring Plowing Desirable for Green-Manure Crop 242 Difficulties Encountered With Fall Plowing 243 Effects of Harvesting a Fall Hay Crop 244 Use and Comparative Value of Sweet Clover As a Pasture Crop 245 Problems in Pasturing Sweet Clover 246 Place of Sweet Clover in the Rotation 247 Clipping Sweet Clover 248 Harvesting Sweet-Clover Hay 248 Harvesting the Seed 251 Sweet Clover Has Merit As Bee Pasture 254 CULTURE OF SWEET CLOVER 255 Time of Seeding 255 Method of Seeding 256 Rate of Seeding 256 Nurse Crops 257 SWEET-CLOVER DISEASES 258 Mosaic 258 Root Rot 258 Other Diseases 258 INSECTS AFFECTING SWEET CLOVER 259 Clover Leaf Weevil 259 Grasshoppers 259 Grape Colaspis 259 Clover Stem Borer 259 SUMMARY 260 LITERATURE CITED.. .262 Urbana, Illinois July, 1933 Publications in the Bulletin series report the results of investigations made by or sponsored by the Experiment Station SWEET CLOVER IN ILLINOIS By O. H. SEARS, Associate Chief in Soil Biology, J. J. PIEPER, Associate Chief in Crop Production, and W. L. BURLISON, Chief in Crop Production , WEET CLOVER is an old plant 1 but a new crop in Illinois. The rapid rise of sweet clover to a place of prominence in the agricul- ture of the state and the nation is abundant evidence of its true worth. It is widely distributed over Illinois (Figs. 1 and 2) and now ranks first in acreage among the legume crops. Sweet clover has not replaced other legumes but has won its own position in the agriculture of the state. Altho definite figures are lacking, it is believed that among the important legumes sweet clover ranks near the top in acre- age in the United States. Experimental work with sweet clover was started by the Illinois Agricultural Experiment Station in 1905. These studies have been ex- panded and continued up to the present. This publication reports the results of experiments made as early as 1917 and as late as 1932. DESCRIPTION OF PLANT Sweet clover is an erect-growing legume with trifoliate leaves and white, yellow, or purple flowers. It is similar to and closely related to alfalfa and the true clovers (Fig. 3). In its early stages it is difficult to distinguish from alfalfa (Fig. 4). All sweet clovers have a bitter taste and have, when bruised, a characteristic pleasant odor due to a substance within the plant known as cumarin. The common sweet-clover species are either annual or biennial in growth, altho strains are being studied at the Illinois Station which, when grown in the greenhouse, have produced more than one crop of seed. The annual species usually range from 2 to 5 feet in height and have many stems but few leaves. The root system is small compared with that of the biennial forms. The annuals bloom late in the season and mature seed the first year. J The history of sweet clover dates back two thousand years to a time when it was used as a green-manure crop and as a honey plant in the early agriculture of the Mediterranean region. The first observations on sweet clover in the United States were made on the wild crop in Virginia in 1739, more than thirty- five years before the Declaration of Independence. Its real worth was not dis- covered, however, until about twenty years ago. 8 * *These numbers thruout the text refer to literature citations, page 262. 211 212 BULLETIN No. 394 [July, While there is considerable variation, most biennial species have a semi-erect habit of growth the first year (Fig. 5), and grow erect the second year. Under favorable conditions they attain a height of 18 to 30 inches during the first season and store up an abundance of food FIG. 1. DISTRIBUTION OF SWEET CLOVER IN ILLINOIS IN 1932 The growing of sweet clover is not limited to any one section of Illinois. Interest in seed production, good dairy cattle pasture, and soil improvement are responsible in part for the centers of high sweet-clover acreage. reserves in a large, thickened root. The second-year shoots start from crown buds and develop a much-branched plant with comparatively few leaves. The flowers are produced on long flowering stems, or racemes, which arise in the axils of the leaves. A raceme may bear as many as a hundred flowers. Most strains of white sweet clover (Melilotus alba) usually begin blooming in June about ten days after the yellow- flowered species {Melilotus officinalis). Blooming begins at the base of the raceme and continues to the tip (Fig. 6). The normal blooming period for a single stem is ten days to two weeks, usually with not more than half the flowers on the raceme in bloom at one time. The shorter blooming period of the yellow species is due to the more rapid opening of the flowers. 1933] SWEET CLOVER IN ILLINOIS 213 About a month is required for sweet-clover plants to mature seed after blooming. Since new racemes may be formed and blooming con- tinue over a long period, ripe seed may be shattered while the plant is still in flower. Usually one seed is formed in a pod but occasionally two are found. The seed pod comprizes about 20 percent of the weight of the entire fruit. 13 * Seeds of sweet clover and alfalfa are often confused because of their similarity, tho sweet-clover seeds are comparatively short and 900 BOO 700 600 b M 500 ^400 *300 200 100 rl I I I I 1919 W> '21 '22 '23 '24 '25 '26 '27 '28 '29 '30 '31 SJ2 FIG. 2. TREND IN SWEET-CLOVER ACREAGE IN ILLINOIS That Illinois farmers recognize the value of sweet clover is shown in the above chart by the phenomenal increase in sweet-clover acreage. thick and alfalfa seeds are bean-shaped (Fig. 7). Some unhulled seeds are frequently found in a sample of sweet clover. Sweet-clover seeds have a characteristic bitter taste and sweet odor and are slightly larger than those of red clover. Pollination studies with sweet clover indicate that the different species vary somewhat with respect to method of fertilization. 3 * The biennial white-flowered sweet clover, M. alba, and the biennial yellow- flowered M. suaveolens will produce considerable seed in the absence of pollinating insects, while the biennial yellow M. officinalis and the Hubam, M. alba annua, produce almost no seed without the aid of insects. Biennial white sweet clover, the biennial yellow species M. suaveolens and Hubam are all self -pollinated to a large extent, while the biennial yellow species M. officinalis is practically self -sterile. Crossing between the white and yellow species of sweet clover is pos- sible but very rarely takes place naturally in the field. Crosses between 214 BULLETIN No. 394 [July, FIG. 3. GROWTH HABITS OF YOUNG ALFALFA PLANT (A) COMPARED WITH YOUNG SWEET-CLOVER PLANT (B) Note the early crown development on the alfalfa plant, seeded August 26. Crown buds are present on the sweet clover, seeded August 17, but will not resume active growth until the second year. (Photographed November 16, 1931) white strains such as biennial white and Hubam are common. There is no proof for the belief that alfalfa and sweet clover cross-fertilize. SPECIES OF SWEET CLOVER There are more than twenty-five known species of sweet clover grown in various parts of the world. While fully half of these have been tried out in the United States, only seven species are promising. Of the eight species tested at the Illinois Station, the following have merit: MeUlotus alba, common biennial white-flowered sweet clover; M. alba annua, Hubam sweet clover; M. officinalis, common biennial yellow sweet clover; M. suaveolens, a biennial yellow sweet clover; and M. dentata, a biennial white sweet clover. The first three species 1933] SWEET CLOVER IN ILLINOIS 215 can be purchased on the market at the present time. M. indica, an annual yellow species, can also be had on the market but it is not adapted to Illinois conditions. Biennial White-Flowered Sweet Clover By far the most important of all species of sweet clover is the biennial white-flowered sweet clover, Melilotus alba, which constitutes about 80 percent of all the sweet clover grown in the corn belt. 2 * The B FIG. 4. LEAVES OF SWEET-CLOVER SEEDLINGS (A) AND ALFALFA SEEDLINGS (B) One of the most noticeable differences between sweet clover and alfalfa is in the size and shape of the appendages or stipules at the base of the leaf stem, particularly in the seedling stage. varieties and strains within this species are very different, varying in size, habit of growth, productiveness, and date of maturity (Fig. 8). Ten or more varieties and many regional strains of this species have been tried out at the Illinois Station. 1 x Most of these varieties were furnished by the U. S. Department of Agricul- ture, Bureau of Plant Industry, Office of Forage Crops and Diseases. 216 BULLETIN No. 394 [.July, The common commercial variety as purchased on the market is rather variable. During the first year it frequently grows to a height of 18 to 30 inches, the second year to 4 to 7 feet. It comes into full bloom in June or early July and may be classed as medium in date of maturity. This variety is very large and coarse. FIG. 5. Two TYPES OF SWEET CLOVER AS THEY APPEARED IN THE FALL OF THE FIRST YEAR The habit of growth of various strains differs markedly. The strain on the left, which is typical of most sweet clover, grew erect to a height of 30 inches, while the one on the right exhibited a spreading type of growth. Grundy County sweet clover is the most important definite variety belonging to the biennial white-flowered species. It was developed in Grundy county, Illinois, about 1917. Because of its uniformity of growth and maturity, it is well adapted for seed production. It rarely attains a height above 4 feet, and matures all its seeds at about the same time so that shattering is not a serious factor. Seed yields of 10 bushels or more an acre are not uncommon. It matures ten days to two weeks earlier than the common commercial variety, and for that reason is not well adapted for late summer and fall pasture. Because of its finer stems and favorable leaf production, Grundy County makes better hay than the larger, coarser varieties. It furnishes an abundance of material for green manure, and is easier to turn under when full grown than are the larger varieties. It is an early, medium-sized strain. Arctic sweet clover was developed by the University of Saskatche- wan from seed which was probably of Siberian origin. It is most 193J\ SWEET CLOVER IN ILLINOIS 217 promising in the Northwest, where earliness and winter hardiness are desirable characters. This variety gives good yields of seed. Since it is very early and very low growing, it is doubtful if it will become important in this section. FIG. 6. BRANCH OF SWEET CLOVER SHOWING BUDS, FLOWERS, AND MATURE SEEDS The habit of continuous seed production over a relatively long period com- plicates the harvesting of seed. Early harvesting results in a mixture of green and mature seed, while late harvesting is accompanied by much shattering. Parker's Hubam- Biennial Hybrid is large in size and medium to late in maturity. It is very leafy and appears to be a promising variety. Crystal Dwarf is early, of medium height, and fine-stemmed. Chatlands Late Dwarf is very large but medium-late. Late White is large, coarse, and medium-late. Van Wirt County is similar to Grundy County in time of maturity but is very large. Taylor's Acid-Soil Resistant, 218 BULLETIN No. 394 Stone's Early, Taggart's Uniform Ripening, and a number of other varieties have not been grown extensively enough to determine their characteristics. In addition to these more than twenty commercial lots and regional strains have been tested, and while they vary in habit of growth, there seems to be no regional seed adaptation problems with sweet clover as in the case of certain other legumes. Annual White-Flowered Sweet Clover Hubam (Melilotus alba annua) is the only important variety in the group of annual white-flowered sweet clovers. 14 * The strains within this group vary widely. S. M. Tracy reported finding annual sweet-clover plants as early as 1898. 10 * The Illinois Agricultural Experiment Station recorded com- FIG. 7. SEEDS OF SWEET CLOVER (LEFT) AND ALFALFA (RIGHT) Tho there is a close resemblance between sweet-clover seeds and alfalfa seeds, they can be distinguished by their shape. Alfalfa seeds tend to be bean- shaped, while sweet-clover seeds are oval. Magnified 5 times. parative yields of the annual and biennial forms in 1914 and took photographs of them. In 1917 five bushels of seed were harvested and in 1918 ten acres were sown to this new legume. Hubam sweet clover was introduced as a field crop by H. D. Hughes of the Iowa Agricul- tural Experiment Station in 1916. Hubam sweet clover grows to a height of 2 to 5 feet. The plant has numerous strong stems with few leaves; the roots are small without crown buds. It blooms from the middle of July to the middle of Sep- tember. Seeds, which cannot be distinguished from those of the bi- ennial species, are matured the first year. Seed production, however, cannot be relied upon in the northern regions. 1933~\ SWEET CLOVER IN ILLINOIS 219 During the year in which it is sown, Hubam clover produces more top growth than the biennial white sweet clover but the root growth of the biennials is very much greater than that of Hubam. 18 * Considering total yield of dry matter and total protein, biennial white sweet clover FIG. 8. SWEET CLOVER STRAINS VARY CONSIDERABLY IN TIME OF MATURITY Strain A showed no buds on July first; Strain D was just coming into bloom; Strain B was in full bloom; while Strain C had almost completed blooming and had formed seeds. under most conditions is to be preferred to Hubam for green manure and forage. Where sweet clover is to be fall-plowed, Hubam has some advantages. As a bee pasture Hubam clover has gained much favor. It is also a good seed-producer. Biennial Yellow-Flowered Sweet Clovers There are two more or less important species of biennial yellow- flowered sweet clover Melilotus officinalis and Melilotus suaveolens. The two are similar in many respects, tho M. suaveolens is probably more productive, more winter-hardy, somewhat taller, finer stemmed and leafier, and later in maturity than M. officinalis. The latter is more widely grown and is the species usually thought of in this group. Very little experimental work has been done with M. suaveolens. The biennial yellow sweet clover M. officinalis usually grows in a more prostrate position the first year than the biennial white sweet clover. It grows erect the second year. It usually grows to a height of 3 to 5 feet and matures ten days to two weeks earlier than the white species. A larger proportion of the plant is roots, but because of the greater fineness of the stems and leaves, it does not produce so much 220 BULLETIN No. 394 [July, forage or green manure as the white biennial. Because of its uniform- ity it is a good seed-producer. The seeds are about the size of those of the white-flowered species, but they are often mottled with purple. Observations at the Illinois Station indicate that M. officinalis is more drouth-resistant and acid-tolerant than the white species. As a hay FIG. 9. SWEET-CLOVER BREEDING PLOTS SHOWING FIRST YEAR'S GROWTH Since commercial strains of sweet clover are made up of many types, it is comparatively easy to select strains that vary in size, time of maturity, and disease resistance. (Photographed November 4, 1931, Urbana). plant the yellow species have some desirable characteristics, but they are not recommended for pasture because of their early maturity. Albotrea is probably the best-known variety of the species M. offi- cinalis. It has been grown in Canada and the northern states for some time and is increasing in popularity. The character of growth and the yields are similar to those of most commercial strains. For the present at least it is not to be given preference to the white species under Illinois conditions. Annual Yellow-Flowered Sweet Clovers Of the several species of annual yellow-flowered sweet clover, Melilotus indica is the most important. It is a very small, very early sweet clover which has no value in Illinois. It is known as sour or bitter clover. The seeds are small, rough, and dark green, and can easily be distinguished from those of other species of sweet clover. Varieties for Illinois Sweet-clover varieties and strains are being developed and adapted to almost every condition and use (Fig. 9). There is a demand for a 19331 SWEET CLOVER IN ILLINOIS 221 late-maturing, medium-sized plant that can be used to better advantage for pasture. It is important that such a strain be uniform and a good seed-producer. Several such selections are being studied at the present time at various agricultural experiment stations including Illinois (Fig. 10). As a general rule the biennial white-flowered species are to be recommended under Illinois conditions. The yellow-flowered species FIG. 10. SELECTED STRAINS OF WHITE SWEET CLOVER Strains of white sweet clover selected from individual plants exhibit striking uniformity, thus making it possible to develop strains well suited to a particular set of conditions. that have been tested have no outstanding characteristics to warrant a change at the present time from the general practice of growing white sweet clover in Illinois. It is important to maintain the purity of varieties ; this can be done most effectively by growing a few of the best strains. CLIMATIC AND SOIL REQUIREMENTS OF SWEET CLOVER Sweet clover thrives under a wide range of climatic and soil con- ditions. It is adapted to a wider range of climate than is alfalfa or any of the true clovers. It is more drouth-resistant than red clover or alfalfa, yet it is well adapted to the more humid regions. This new crop is equally adapted to high or low temperatures. Under proper cultural conditions sweet clover is seldom winterkilled in Illinois. When inoculated, sweet clover will grow in practically any nonacid soil in Illinois (Fig. 11). Altho it frequently grows well on badly eroded hill lands that are so unproductive that general farming is un- 222 BULLETIN No. 394 [July, profitable, it is at its best on soils suited to the growing of corn, wheat, clover, and alfalfa. Good drainage, the absence of acidity, an adequate amount of available phosphate and potash, and a plentiful supply of active organic matter contribute to an excellent growth of sweet clover on Illinois soils. Drainage Is Beneficial But Not Essential Altho the growth of sweet clover is improved by good drainage, this crop may be grown successfully on soils which are too poorly FIG. 11. SWEET CLOVER GROWING ON BANK OF A DREDGE DITCH Sweet clover will grow on nearly any soil in Illinois that contains an abun- dance of lime. Even on soils low in organic matter sweet clover makes an excellent growth. It is a good plant to use to prevent or check erosion. drained for satisfactory results with alfalfa and red clover. Even on the flat, light-colored soils of Illinois which are underlain with a more or less impervious subsoil, sweet clover grows remarkably well where sufficient limestone is supplied (Fig. 12). While there is no experi- mental evidence to support the claim, some farmers believe that the natural drainage on these soils is improved by the repeated growing of sweet clover. It is a matter of record that the plots on the Illinois soil experiment fields growing this crop may usually be plowed earlier in the spring than adjoining plots on which sweet clover is not grown. An improvement in the physical condition of the surface soil and the transpiration of water by the growing crop undoubtedly contribute to this "earliness" of the sweet-clover land. 1933~\ SWEET CLOVER IN ILLINOIS 223 Sweet Clover Demands a Sweet Soil Sweet clover seldom grows satisfactorily on sour soils (Fig. 14). Because sweet clover has a high calcium content and makes a rapid and extensive growth, it requires a large amount of lime in a compara- tively short time. Under Illinois conditions the lime requirement of this crop is greater than that of any other crop grown. Unless the soil has an adequate supply of lime in available form, the crop suffers from lack of calcium. Even on soils that will produce a mediocre stand of alfalfa, sweet clover frequently fails completely. Sweet-clover plants FIG. 12. SWEET-CLOVER ROOT DEVELOPMENT ON LIMED LAND THAT ORIGINALLY WAS VERY ACID AND HAD AN IMPERVIOUS SUBSOIL Sweet clover does not generally penetrate the subsoil on limed land that has a very acid impervious subsoil. The roots are usually branched and gnarled. may grow for a short period on such a soil, but unless a less acid con- dition exists near the surface of the soil than exists at the surface, the plants soon sicken and die. Sweet-clover nodule bacteria also are injured by acidity. Under acid conditions they are either killed or their vitality so lowered that they are unable to perform their usual functions of supplying the sweet-clover plant with available nitrogen compounds. Another reason for the failure of sweet clover on distinctly sour soils is that under Illinois conditions a low amount of available phos- phorus is usually associated with acidity. While the evidence is some- what meager on this point, there are indications that liming an acid soil not only creates a more favorable soil reaction but also may affect the amount of available phosphorus present. 224 BULLETIN No. 394 {.July, To sow sweet-clover seed on soils of high acidity is to throw away both seed and money. This fact is well illustrated by the data obtained from various soil experiment fields in the state. In Table 1 are shown yields of hay from eight fields located on dark-colored soils, the cut- FIG. 13. DEEP ROOT SYSTEM OF SWEET CLOVER The root system of sweet clover consists mainly of a tap root that ordinarily penetrates the soil to a depth of 3 or even 5 feet where the subsoil is not acid and is well drained. tings being made in the fall of the year in which the sweet clover was seeded. The use of limestone resulted in an average increase of .96 ton (1,920 pounds) of hay an acre for the 22 crops grown on these eight fields. This increase (343 percent) becomes even more signifi- cant when it is noted that on two of these fields, Hartsburg and Minonk, there was no important increase that could be attributed to the limestone applications. Obviously the growing of sweet clover should not be attempted on 1933} SWEET CLOVER IN ILLINOIS 225 FIG. 14. SWEET CLOVER REQUIRES A SWEET SOIL The plot on the left was unlimed and would grow no sweet clover. The addition of limestone was responsible for the excellent stand of sw r eet clover on the right. soils that are distinctly sour, such as those represented by the Aledo, Carthage, Clayton, LaMoille, and Lebanon fields, unless lime is applied. On the other hand, there appears to be little advantage in liming soils that are already supplied with constituents that the limestone carries ; the Hartsburg and Minonk fields represent such soils. Beside varying greatly from one locality to another in their need for limestone, soils frequently vary also from place to place within the TABLE 1. INFLUENCE OF SOIL TREATMENT ON YIELDS OF SWEET-CLOVER HAY ON DARK-COLORED ILLINOIS SOILS: FALL CUTTING Field Number of crops Yields per acre with R RL RLP RLPK Aledo 3 2 4 2 1 6 2 2 22 tons .18 .21 .63 .12 1.19 .59 .28 tons 1.60 1.01 1.11 .71 1.69 1.53 1.16 .73 1.24 tons 1.66 1.32 1.38 .82 1.77 1.55 1.33 .74 1.36 tons 1.90 1.61 1.50 .82 2.03 1.63 1.50 1.09 1.53 Carthage Clayton. Hartsburg LaMoille Minonk Springvalley NOTE. The soil treatment in this and following tables is designated by the following symbols: = None R = Residues (residues from crops, and legumes used as green manure) M = Manure MP = Manure and rock phosphate RP = Residues and rock phosphate ML = Manure and limestone RL = Residues and limestone MLP = Manure, limestone, and rock phosphate RLP = Residues, limestone, and rock phosphate RLPK = Residues, limestone, rock phosphate, and potassium (usually in the form of kainit) 226 BULLETIN No. 394 Uuly, same field. The amount of limestone to be applied to a field where sweet clover is to be seeded should therefore be determined by a syste- matic test of the area. For further information on this phase of the liming problem, see Circular 346 of this Station, "Test Your Soil for Acidity." 5 * Limestone Need Greater on Light-Colored Soils Altho there are many exceptions to the rule, in general the light- colored soils of the state, particularly those of southern Illinois, have a greater need for limestone than have the dark-colored soils. Not only is a larger percentage of the light-colored soils sour, but a greater quantity of limestone an acre must be applied before these soils will grow clover successfully. Hay Yields Increased by Use of Limestone. The increased yields obtained from the use of limestone on the Odin and Sparta experiment TABLE 2. INFLUENCE OF SOIL TREATMENT ON YIELDS OF SWEET-CLOVER HAY ON LIGHT-COLORED ILLINOIS SOILS: FALL CUTTING Soil treatment Odin field- average yield per acre from three crops Sparta field yield per acre from one crop . , tons tons M ML .96 MLP .99 MLPK .94 R RL .72 RLP .72 RLPK 1.12 fields are representative of the results obtained on many of the light- colored soils in the southern part of the state (Table 2). Sweet clover is a complete failure on these fields where no limestone has been ap- plied. On the limed plots a fair to good yield of hay is obtained, the amount depending greatly upon the summer and autumn rainfall. Even after adequate liming, these light-colored soils may produce only a mediocre stand of sweet clover the first time. Subsequent seed- ings, however, are usually more satisfactory. The amount of acidity in the soil, the rate at which the lime is applied, and the fineness of the limestone will all affect the success of the first crop, as will also the method of distributing the limestone and the time elapsing between the 1933] SWEET CLOVER IN ILLINOIS 227 TABLE 3. INFLUENCE OF SOIL TREATMENT ON YIELDS OF SWEET-CLOVER HAY CUT IN THE SPRING, ILLINOIS EXPERIMENT FIELDS Soil treatment Dark-colored soil 8 average yield per acre from 2 crops Light-colored soil 1 " average yield per acre from 3 crops Sand soil average yield per acre from 4 crops tons .28 tons tons M .27 ML 1.67 1.30 1.20 MLP. 1.79 1.65 1.26 R. . .41 RL 1.80 .71 1.81 RLP 1.73 1.05 1.66 RLPK 1.83 1.57 2.29 "Carlinville. b Elizabethtown and Enfield. Oquawka. application and the seeding of the crop. Limestone is comparatively insoluble in water, and before it can correct the acidity of the soil it must dissolve. Altho sweet-clover hay is less desirable when cut in the spring of the second year than when cut during the first year's growth (see page 249), the use of limestone increases the yield of hay in both cases (Tables 1, 2, and 3). This increase is apparent on both light- and dark- colored soils, tho more limestone is needed on the light-colored soils. Seed Production Affected Less Than Hay Yields by Soil Acidity. Yields of sweet-clover seed and hay are sometimes affected similarly by liming, and sometimes very differently, as shown in Tables 3 and 4 by the seed yields for the seven fields of light-colored soils and for the two fields of acid sand soils. On the light-colored soils even the limed plots produced a comparatively low seed yield, while the unlimed plots TABLE 4. INFLUENCE OF SOIL TREATMENT ON YIELDS OF SWEET-CLOVER SEED, ILLINOIS EXPERIMENT FIELDS Soil treatment Dark-colored soil" average yield per acre from 3 crops Dark-colored soil b average yield per acre from 1 crop Light-colored soil average yield per acre from 33 crops Sand soil 11 average yield per acre from 14 crops . . bu. 3.82 bu. 5.17 bu. .04 bu. .03 M 4.28 .04 .11 ML 3.24 1.78 1.65 MLP 3.10 1.73 1.67 R.. . 4.50 .07 .10 RL 6.42 1.62 1.87 RLP 4.67 1.44 1.95 RLPK 3.83 2.11 2.08 Mt. Morris. b Carlinville. "Elizabethtown, Enfield, Ewing, Oblong, Odin, Sparta, and Toledo. d Oquawka and Palestine. 228 BULLETIN No. 394 [July, yielded no seed because no sweet-clover plants survived. On the two fields of dark-colored soils where the acidity is too great for a maxi- mum yield of sweet-clover hay but not sour enough to inhibit plant growth completely, a low seed yield was obtained without liming. The low yield of seed on the unlimed plots of the dark-colored soils is due primarily to the poor stand of plants caused by the acid condi- tion of the soil, altho the plants are also less thrifty than those on the limed plots. Curiously enough the yield of sweet-clover seed is less markedly affected by the number of plants than is the hay yield. This is explained by the fact that if the number of plants per acre is large, the size of each plant is comparatively small and the amount of seed per plant is likewise small ; whereas if the number of plants per acre is small, the size of the individual plants is large and the amount of seed per plant is proportionately large. Thus on the Carlinville field the yield of hay was increased sixfold by liming (Table 3), whereas the average seed yields were no higher on the limed than on the un- limed plots (Table 4). It is not to be inferred that liming may not increase the yields of sweet-clover seed, but rather that the effect of limestone application on hay yields is more pronounced than the effect on seed. Sweet Clover Responds to Phosphates As with alfalfa, the growth of sweet clover is improved by the use of phosphates where the available soil supply of phosphorus is low. Thus sweet clover may be grouped with those crops that are considered responsive to phosphate fertilization. On many soils in Illinois, however, the lack of phosphorus does not appear to be a factor controlling the yields of sweet clover. This fact is shown by the data in Tables 1, 2, 3, and 4 on pages 225, 226, and 227. In Table 1 the average increase shown in hay yields on eight experiment fields is only .12 ton for phosphate. On two of the fields, Carthage and Clayton, substantial gains were obtained from the use of rock phosphate ; on the other six fields small or no increases resulted from the use of this material. The need for phosphate, as for limestone, varies not only from field to field but from area to area within a given field. It is therefore important to test the various parts of a field for available phosphates before applying any phosphate. A method for making such tests is now available and is described in Bulletin 337 of this Station, "A Field Test for Available Phosphorus in Soils." 1 * Altho the data presented in Table 4 are too meager for conclusive proof, it appears that the need for phosphate fertilization is no greater 1933~\ SWEET CLOVER IN ILLINOIS 229 where sweet clover is grown for seed than where the crop is used for hay. Potash Is Important on Many Soils Sweet clover is responsive to potash fertilization as well as to phos- phate fertilization. This is evidenced by the differences in yields attrib- utable to these elements in Tables 1 to 4, as well as by the large per- centage of the fields showing gains for potash treatment. In Table 1, giving the results on dark-colored soils, hay yields are shown to have been increased an average of .17 ton an acre where potash was applied in addition to residues, limestone, and phosphorus, and on half the fields the gain w r as .25 ton or more. The gain for phosphorus in addi- tion to residues and limestone was .12 ton an acre. On the light- colored soils in particular, the benefits from the use of potash salts is marked (Tables 2, 3, and 4). This need for potassium is not the result of a low total supply in these soils, but is due in part at least to the low availability of this element. While it is possible to grow fair or good sweet clover on most soils in Illinois without the use of potash salts, the best results are likely to be obtained where potassium-containing fertilizers are used. Manure Aids in Securing Stand The importance of manure in securing a stand of sweet clover is not to be overlooked. Frequently only half a stand or less is obtained the first time sweet clover is seeded on recently limed soil, especially where a rather large initial application of limestone was required to sweeten the soil. In such instances a marked improvement in stand usually results from a light dressing of farm manure. At least two conditions contribute to this beneficial effect. In the first place, for several months after limestone has been applied only the soil immedi- ately surrounding the limestone particles has its acidity neutralized, and consequently many of the nodule bacteria, which, as already pointed out, are adversely affected by acid soil conditions, die before the sweet-clover plants have established themselves. The manure pro- vides an immediately available food supply for the plant and for the bacteria that are not killed, and so the sweet-clover plants are enabled to survive until such time as the nodule bacteria are able to furnish the crop with nitrogen from the air. In the second place, the potassium contained in the manure aids in the development of the plant, as men- tioned previously. Thus the difference between a poor and a good stand of sweet clover at the first seeding may be determined by the use of manure. 230 BULLETIN No. 394 [July, It is not to be assumed, however, that the application of manure can replace other kinds of soil treatment, particularly limestone. Sweet clover, as may be seen from Tables 2, 3, and 4, is a failure on sour soils where no limestone has been applied, even tho manure is used. Manure is a good supplement for limestone but it is not a substitute ; it aids in obtaining a good stand after the soil has been limed. Inoculation Necessary for Success With Sweet Clover Alfalfa was a failure in Illinois until the importance of inoculation was discovered. Likewise sweet clover, which is somewhat similar to alfalfa in its growth habits and which is infected by the same nodule organism, cannot be grown successfully unless the soil is properly in- oculated. Natural inoculation occurs in some soils, particularly in those where alfalfa or wild sweet clover has grown. On most land, however, where neither of these crops has grown previously, lack of inoculation results in failure of the crop. The chief advantage in inoculating the crop is the heavier growth that results. Regardless of whether the sweet clover is grown for soil- improvement purposes, for hay, or for pasture, it is important to secure as much plant growth as possible, particularly during the first season. Because of the large amount of nitrogen required by the crop, maxi- mum growth is impossible on most soils in the absence of the nodule bacteria. Results obtained at this Station 12 * indicate that as much as 250 pounds of nitrogen may be contained in the roots and tops of an acre of sweet clover. Only unusual soils would be able to supply such an amount of available nitrogen during the growing season of the crop ; consequently air nitrogen must be available if high yields are to be ob- tained. Assuming that two-thirds of the total nitrogen in the plant is derived from the air, 100 to 150 pounds of nitrogen an acre may be added to the soil during a single year if the nodule bacteria are func- tioning on the roots of the sweet-clover plant. Unless the soil is prop- erly inoculated, however, no addition of nitrogen occurs. The protein content of sweet clover, as of other legumes, is in- creased by inoculation. Since protein is one of the most expensive of feed constituents, inoculation is of importance to the livestock man who desires to use the crop for hay or pasture. For soil-improvement pur- poses, likewise, it is important that sweet clover have a high nitrogen content so that it will decay more readily and thus release available plant nutrients for succeeding crops. Methods of Inoculation. The method first employed for the inoc- ulation of legumes, particularly for alfalfa, consisted of a direct trans- 1933} SWEET CLOVER ix ILLINOIS 231 fer of soil from a field or area where the crop previously had shown good nodule development. In this process several hundred pounds of soil was spread on each acre of land. Altho this method gave satis- factory results, it was expensive and in addition was likely to introduce weed seeds and disseminate plant diseases. Consequently it was gen- erally abandoned a few years ago for methods more economical of time and labor. A modification of the direct soil-transfer method of inoculation, which has been used extensively in Illinois, is the so-called "muddy water" method. A measured quantity of well-inoculated soil is added to an equal amount of water. The soil is stirred for approximately five minutes to break up the lumps of soil and permit the bacteria to be washed into the muddy water. The soil is allowed to settle for another five minutes, and the trash is removed from the surface of the liquid. One pint of this muddy water is sprinkled over each bushel of seed. The seeds are stirred until all are moistened; then they are allowed to dry in the shade and are sown at once. (Drying may be hastened by sprinkling some of the dry soil on the wet seed and stirring again.) It is important that the soil be obtained from a field in which alfalfa or sweet clover has shown abundant nodule development; the mere fact that one of these crops grew in a field is not assurance that the soil will give satisfactory inoculation. Preferably the soil should be taken from around the roots of well-inoculated plants. Commercial inoculants are now being distributed by a number of concerns and, like most products, they differ greatly in their efficiency. The best commercial inoculants, however, are very satisfactory from the standpoint of successful inoculation and are comparatively easy to use, especially if the directions given for their use are followed. The cost of commercial inoculants for sweet clover is slight, varying from 5 to 20 cents an acre. SWEET CLOVER AS A SOIL BUILDER The first recorded use of sweet clover for soil improvement, accord- ing to Pieters, 9 * was on abandoned tobacco fields of Kentucky. He states that "these limestone soils were cropped out and many of the farms were abandoned ; washing of the slopes became serious and the land was practically useless. As the farmer moved out, the wild sweet clover moved in, covered and protected the surface, opened the subsoil, and in dying left new stores of humus and nitrogen in the impoverished surface soil. One generation of sweet clover followed another, until someone discovered that the once barren soil was rich again." Wher- 232 BULLETIN No. 394 ever sweet clover has been used in the corn belt, its worth for soil- improvement purposes is generally recognized. Increased Crop Yields Follow Sweet Clover In this discussion the term soil improvement applies to those prac- tices that result in a greater capacity of the soil to produce crops under any given condition. That sweet clover is a soil-improving crop is well illustrated by the data shown in Tables 5, 6, and 7. Where sweet clover has been grown, not only has the first succeeding crop been larger but subsequent crops have also been affected favorably. TABLE 5. EFFECT OF SWEET CLOVER AND MANURE ON CORN YIELDS ON DARK-COLORED ILLINOIS SOILS, 1928-1931 Plots Field 1,5, 10 None Plot 2 M Plot 6 R Plot 3 ML Plot 7 RL Plot 4 MLP Plot 8 RLP Plot 9 RLPK Yields per acre on soils requiring liming Aledo bu. 49 bu. 67 bu. 58 bu. 67 bu. 67 bu. 68 bu. 69 bu. 71 Carlinville 27 35 27 38 33 39 33 36 Carthage 37 53 51 63 61 63 62 65 Clayton 39 62 48 71 59 72 58 67 44 65 48 72 60 71 59 68 Kewanee 55 71 65 78 74 78 75 77 46 60 56 61 62 62 62 64 36 48 46 54 65 53 65 69 Mt. Morris 43 58 51 73 64 71 67 67 Springvalley 36 52 48 57 49 60 45 57 Average 41 57 50 63 59 64 60 64 Yields per acre on soils growing sweet clover without liming Hartsburg 43 54 68 65 71 64 71 64 Minonk 45 57 57 64 61 61 61 58 Average 44 56 63 65 66 63 66 61 TABLE 6. INFLUENCE OF GREEN MANURES ON CROP YIELDS, OHIO EXPERIMENT* (Yields per acre, average of 4 crops) Cc rn Oc its Yield Increase Yield Increase None bu. 31.3 bu. bu. 40.9 bu. Red clover 39.1 7.8 42.7 1.6 Mammoth clover 38.8 7.5 44.8 3.9 49.4 18.1 49.9 9.0 Data from Forty-Fifth Annual Report Ohio Agricultural Experiment Station, Bulletin 402, Table 3, page 18. See also Ohio Bulletin 405. 16 * 1933] SWEET CLOVER IN ILLINOIS 233 o M u z as O U a 3 2nd crop m^">~*-Oi .g -o 10 * o >oi 00 1 1st crop a o wjinotsm ^ r^i^-*>OvOO a, a 2nd crop a oi'J'O- * ^ >O irt ^ -O 10 10 1 i 1st crop a t~'*OQ--'J < ^ sOOsO>0 j 3 2nd crop a fO o ^ o\ o* if) .S omn^ioioio treatment o 1st crop a oc r-ovO-H .S ^t^fOiOOO erent soil J S 2nd crop a ooot^'*^ o> ^ eioio under diff 'o 1st crop a t^. in ^ _~ \O\OU5~O-O >O 2 "5 a 1 a ^* o &> t'* oo f*5 1 ts < 1 1st crop a tsS(SOt~>/ ^ "Oul^i^lOlO a u jj Tj. 0, -H ^. ^1 O> I 3 ts "o s 1st crop a "iovo>ts>o O CSI/5IOIO I 2nd crop a -H o * i- * ^ UlTf WJ Tf ^. T(< g S 1st crop a >^. ~ c c "-. ^ ^"t CS Tt Tj> Tj< o 3 .s : B : : & :5 :==^2 ll!!l< 234 BULLETIN No. 394 [July, Sweet clover grows well on the Minonk and Hartsburg fields with- out the application of limestone (Table '5 ). By comparing Plot 6 (residues) with Plots 1, 5, and 10 (untreated) it is evident that sweet clover caused a 19-bushel increase in the yield of the succeeding corn crop. Even tho these soils are high in total nitrogen, the sweet-clover crop is responsible for an average increase in corn yields of 20 bushels an acre on all plots. On none of the twelve experiment fields shown in Table 5, except- ing Hartsburg and Minonk, will sweet clover grow on the residue plots in the absence of limestone. Consequently it is impossible to evaluate the benefit secured on these fields from sweet clover alone. By com- paring Plots 6 and 7, however, it is seen that the combined effect of limestone and sweet clover has resulted in an increase of 9 bushels an acre in the yield of corn as an average of all the fields. The greatest gain shown for the limestone and sweet-clover combination is 19 bushels on the Lebanon field ; the smallest increase is 1 bushel on the Springvalley field. Sweet Clover Compares Favorably With Farm Manure. The value of farm manure for improving the yields of crops is generally recognized. Where livestock fit into the farming plan, the pasturing of sweet clover or its use as hay under conditions mentioned on pages 245 and *248 constitutes one of the most satisfactory methods for its utilization. Where little or no stable manure is available, sweet clover may be used very effectively as a green manure, and when used in this way may prove practically as valuable as a moderate amount of stable manure. A comparison of the corn yields obtained on certain plots shown in Table 5 indicates that one is not dependent upon stable manure for soil improvement when sweet clover can be grown. On Plot 7, the residues-limestone plot, and on Plot 8, the residues-lime- stone-phosphorus plot, the yields averaged only 4 bushels of corn an acre less than those on Plots 3 and 4, where manure was used instead of residues. The yields reported in Table 5 include only those from the last rotation on fields where sweet clover had been systematically grown for several rotations. The immediate effect of sweet clover, which is in many cases striking, is illustrated by the yields obtained in a co- operative experiment in Bureau county in 1930. 7 * The soil upon which the trial was made did not require the addition of limestone in order to grow sweet clover. It was, however, low 'in organic matter. A strip of sweet clover was seeded across a 40-acre oat field in the spring of 1929 and the growth plowed down late in the fall of the same year. 1933~\ SWEET CLOVER IN ILLINOIS 235 The part of the field which grew sweet clover produced 52.2 bushels of corn an acre, while the remainder of the field yielded only 24.6 bushels an acre. This increase of 27.6 bushels of corn was obtained at a cost of about a dollar an acre for the sweet-clover seed and a slight addi- tional cost for plowing under the sweet clover. Sweet Clover Superior to Other Green-Manure Crops. Sweet clover, when used as a green-manure crop not only compares favorably with farm or stable manure in its effect upon crop yields, but it is one of the most valuable of the legumes for soil-improvement purposes. In an experiment conducted by the Ohio Agricultural Experiment Station, 15 * a two-year rotation of corn and oats was employed, the clovers being seeded in the oats and plowed under the following spring for the corn (Table 6). When used for green-manuring purposes only, sweet clover proved to be more than twice as effective in this rotation as either of the other two clovers, tho red clover had the advantage of being a better hay crop. The effect of the sweet clover in the Ohio experiments was not con- fined to the first succeeding crop, but its beneficial influence was exhib- ited on subsequent crops. Similar results were obtained with corn at the Illinois Station (Table 7). Where two corn crops were grown in the rotation, one following the other, the second corn crop was also favorably affected by the sweet clover altho it was not so large as the first. Benefits From Sweet Clover Due to Combination of Factors No one factor is responsible for the beneficial effect of sweet clover upon crop yields. This effect is the result of a number of interacting factors improved soil tilth, nitrogen fixation, addition of active or- ganic matter to the soil, an increase in the microorganic life in the soil, and a gain in available plant nutrients. No system of sweet-clover management can be evaluated by taking into consideration only one of these factors. Sweet Clover Improves Soil Tilth. Every farmer knows that soil "works" better at some times than at others. Some years a good firm seed bed is comparatively easy to secure, at other times only a cloddy field can be obtained. In the first case the soil is said to have a good physical condition or to be in good tilth ; in the other case, to be in poor tilth. Unfortunately there is no method of stating quantitatively the degree of tilth in a soil. It is simply a matter of experience that the growing of sweet clover makes it easier to secure a good seed bed. While it is impossible to say what proportion of the increased crop 236 BULLETIN No. 394 [July, yields following sweet clover is the result of better tilth, this factor certainly is deserving of some of the credit. The improved tilth of soil in which sweet clover has been grown is indicated by the fact that it may be worked earlier than soil in which sweet clover has not been grown. This is of particular importance 200 AUG. SEPT. OCT. NOV. DEC. MAR. APR. MAY JUNE JULY FIG. 15. TOTAL NITROGEN DISTRIBUTION IN TOPS AND ROOTS OF SWEET CLOVER AT DIFFERENT DATES DURING THE YEAR Altho the distribution of nitrogen between roots and tops varies greatly with the season, the total nitrogen of the sweet-clover plant increases little after growth ceases in the fall of the first year. when a late spring so delays seeding that an unfavorable cropping season results. The opportunity to get crops started early in the sea- son is also important from the standpoint of crop feeding, for with early planting, crops encounter more favorable moisture, air, and tem- perature relationships conditions responsible for the availability of plant nutrients. 1933~\ SWEET CLOVER IN ILLINOIS 237 Sweet Clover Supplies Soil Nitrogen. Inoculated sweet-clover plants, as discussed on page 230, obtain a large portion of their nitrogen from the air thru the activity of the nodule bacteria on the roots of the plants. The amount of nitrogen which will be added to the soil when the crop is returned to the land will depend upon the composition of the crop, amount of growth, and proportion of nitrogen secured from the air. In experiments made at Illinois by Snider and Hein 12 * (Fig. 15) it was found that about 250 pounds of nitrogen an acre was present during December and June, and approximately 200 pounds during the months of March, April, and May. A conservative estimate would indicate an addition of 120 pounds of nitrogen an acre by fixation. If this nitrogen were evaluated at the price prevailing in fertilizers, it would be worth from $12 to $18. Such an evaluation may be mislead- ing, however, since no intelligent grain or livestock farmer would apply so large a quantity of nitrogen at one time on account of the danger of losses from leaching and from denitrification. The amount of nitrogen contained in the roots of the sweet-clover plants gradually increases during the fall and decreases during the growth of the following spring. There is a corresponding decrease in the top nitrogen in the fall and an increase in the spring. Altho there is a slight gain in the nitrogen content per acre during the spring and early summer, sweet clover contains nearly as much nitrogen in the fall of the first year as it contains at any other time during its life. There- fore, so far as nitrogen additions to the soil are concerned, little is gained by delaying the plowing of sweet clover after the fall of the first year. Increases the Supply of Available Soil Nitrogen. Altho most soils in the state contain a total nitrogen supply sufficient to raise large crops for many years, much of this nitrogen is in a form which is not im- mediately useful for plant growth. Consequently a lack of available nitrogen is the chief factor limiting the growth of crops in Illinois. One of the most striking characteristics of sweet clover is the rapid- ity with which it decays. As a result of the decomposition of the active organic matter which sweet clover supplies, an increase in avail- able plant food elements results. This increase in available nitrogen is illustrated by a comparison of Plots 305 and 306 on the Hartsburg soil experiment field (Table 8). The two plots differ mainly in that Plot 305 was not seeded to sweet clover, whereas on Plot 306 sweet clover was used as a green-manure crop. Since this soil grows a good crop of sweet clover without the application of limestone, the marked in- 238 BULLETIN No. 394 crease in the accumulation of nitrate-nitrogen in Plot 306 can be attrib- uted to the sweet clover alone. Obviously where sweet clover is grown on land of this character the available nitrogen supply will be in excess of the crop requirements until much larger yields are secured by re- moving other limiting factors. Similar increases in nitrate accumulation were obtained by using both limestone and sweet clover on the light-colored soil of the Toledo TABLE 8. EFFECT OF SWEET-CLOVER GREEN-MANURE CROP ON NITRATE ACCU- MULATION ON THE HARTSBURG SOIL EXPERIMENT FIELD Plot Nitrate accumulation per acre on May 3 May 17 June 8 June 22 July 1 July 15 July 29 August 24 Sep- tember 30 306 /6s. 24.6 16.7 7.9 Ibs. 71.0 59.4 11.6 Ibs. 34.7 28.7 6.0 Ibs. 56.9 47.7 9.2 Ibs. 58.3 35.4 12.9 Ibs. 91.5 75.0 16.5 Ibs. 76.9 54.9 22.0 Ibs. 51.1 28.5 22.6 /6s. 42.2 23.1 19.1 305 Difference. . TABLE 9. EFFECT OF LIMESTONE AND SWEET CLOVER ON NITRATE ACCUMULATION ON TOLEDO FIELD Plot Date of plowing Nitrate accumulation per acre on May 14 June 7 June 23 June 30 July 14 July 27 August 25 Sep- tember 29 307 May 16 May 16 /6s. 55.4 34.5 20.9 /6s. 44.5 15.8 28.7 /6s. 25.4 20.5 4.9 /6s. 53.7 34.9 18.8 /6s. 114.2 63.8 50.4 /6s. 77.8 39.4 38.4 Ibs. 34.5 22.0 12.5 /6s. 35.8 26.6 9.2 305 Difference. . field (Table 9). This soil is sour and requires about 4 tons of lime- stone an acre to produce a stand of sweet clover. On May 14, before the sweet clover was plowed under, Plot 307 growing the sweet clover had a 60-percent larger supply of nitrates than Plot 305, which had no sweet clover. These results indicate not only that sweet clover decom- poses readily, causing an increase in nitrates in the soil, but they also suggest that previous sweet-clover crops have a favorable effect upon the power of the soil itself to form nitrate-nitrogen. In addition to supplying a source of organic matter which readily undergoes decay and thereby releases available nitrogen, sweet clover increases the activity of the soil microorganisms which are responsible for the conversion of organic nitrogen compounds already in the soil 1933} SWEET CLOVER IN ILLINOIS 239 into nitrate-nitrogen. Under both greenhouse and field conditions the mere growing of the sweet clover without turning it under appears to have an effect similar to that obtained by adding sweet-clover plants to land which has not grown the crop (Table 10). In an experiment such as that reported in Table 10 it is impossible to remove completely all the roots from the soil. Under greenhouse TABLE 10. RELATIVE YIELDS OF CORN AS AFFECTED BY DIFFERENT METHODS OF USING SWEET CLOVER Where observed No sweet clover Turned under where grown Tops and roots removed Added from other land Field. . ... 100 140 125 105 Greenhouse 100 205 165 180 conditions, it was estimated that 95 to 98 percent of the root growth was removed ; a much smaller proportion was removed in the field ex- periments where the roots were pulled by hand after the soil had been loosened with a spade. However, even tho proportionately a much larger amount of sweet clover was plowed under on the plot which did not grow the clover than was plowed under where the clover crop was removed, the results were about the same, the yields being somewhat less under field conditions and slightly more in the greenhouse. In both the greenhouse and the field the highest yields were obtained where the sweet clover was plowed under where it grew. The benefits thus se- cured by the use of sweet clover appear to be due in part at least to an improvement in the activity of soil microorganisms. Phosphate Makes Sweet Clover a Better Soil Builder Even tho sweet clover is usually effective in increasing the produc- tive capacity of soils, the addition of mineral fertilizing constituents usually has further pronounced benefits. Phosphates and potash salts when used in addition to sweet clover and other residues usually have a more beneficial effect than when employed in a system of livestock farming where manure is supplied. Table 11 shows that the value of crop increases resulting from the use of rock phosphate in addition to limestone and crop residues including sweet clover (grain system) was greater than the value of the increases in the system where rock phos- phate was used with limestone and manure (livestock system). Whether the lower returns for the phosphate in the manure system are due only to the fact that manure serves as a source of phosphorus or are due to some other condition or conditions is not clear. 240 BULLETIN No. 394 [July, TABLE 11. ANNUAL ACRE-RETURNS FOR ROCK PHOSPHATE IN Two SYSTEMS OF FARMING, ILLINOIS EXPERIMENT FIELDS, 1927-1930 8 Field System of farming Difference Livestock Grain Elizabethtown $5.41 4.83 2.66 2.62 2.42 1.29 .97 $7.29 8.51 3.86 2.57 4.27 2.98 1.01 $1.88 3.68 1.20 .05 1.85 1.69 .04 Joliet Kewanee Carthage West Salem Oblong Oquawka 111. Agr. Exp. Sta. Bui. 370, p. 225. 1931. Potash Frequently Improves Corn Yields After Sweet Clover The importance of potassium as a supplementary treatment where sweet clover is grown repeatedly on the land is becoming more appar- ent each year. In Table 12 are recorded certain increases in yields of corn on six Illinois experiment fields resulting from the use of potash salts in addition to crop residues (including sweet clover), limestone, TABLE 12. EFFECT OF POTASH ON ACRE -YIELDS OF CORN DURING FIRST AND LAST ROTATIONS ON Six ILLINOIS EXPERIMENT FIELDS Increases for potash First rotation Last rotation Ewing bu. 3 4 bu. 27.8 Toledo 4.1 16.6 Sparta 2.7 9.6 West Salem .9 9 1 Clayton 2.2 7.7 Carthage 1.5 5.7 and rock phosphate. On all these fields a four-year rotation consisting of wheat (sweet-clover catch crop), corn, oats, and clover is used. This cycle has been completed at least four times on each field. A marked increase in the effectiveness of potassium-containing fer- tilizers occurs as the number of rotations increases. It was believed earlier that most Illinois soils had a sufficient supply of potassium for maximum yields and that the growing of sweet clover would be of assistance in increasing the availability of this element, but it now appears that the need for potassium increases with the repeated grow- ing of sweet clover. 1933] SWEET CLOVER IN ILLINOIS 241 This increased need for potassium is associated with the high nitrate-nitrogen content of the soil which results from the frequent use of sweet clover. Thus in soils with a limited supply of available potas- sium, an increase in the available nitrogen supply may result in an unfavorable ratio of available potassium to available nitrogen. The addition of potassium creates a favorable balance between these two elements. The harmful effect of too much available nitrogen is ob- served only on soils having an inadequate supply of usable potassium and on soils where sweet clover has been grown repeatedly. HANDLING THE SWEET-CLOVER CROP There is no one best way to utilize sweet clover. The choice of the proper method of handling it depends on the kind of farming practiced whether a livestock or grain system on the rotation used, the kind of soil, the amount and kind of power available, and the purpose for which the crop is grown. A plan that is satisfactory on one farm may be entirely unsuited to another. A large proportion of Illinois farmers use sweet clover for both pasture and soil improvement, and probably for many farmers there is no better way of utilizing this crop. When so used, it is usually not plowed under until late in the fall of the second year or in the follow- ing spring. Plow Sweet Clover Green Unless Needed for Pasture The advisability of allowing sweet clover to occupy the land during a second season when the sweet clover is not needed for pasture has been frequently questioned. Tho experimental evidence on this point is incomplete, what evidence there is and observations of farm practice suggest that over a period of years better results are likely to be ob- tained by plowing the sweet clover under while it is green than by per- mitting it to continue on the land a second year, particularly if the land can be used to advantage for growing corn. One disadvantage in permitting sweet clover to mature is the diffi- culty of plowing under the dead material (Fig. 16). Since sweet clover decays readily, the roots are rotted within a few weeks and it is then difficult to plow under the dry tops. In fact some farmers have pre- ferred to lose much of the value of the sweet clover by burning it rather than to attempt to plow it under. It should, of course, be plowed under early in the season while it is still green. A much better stand of sweet clover is frequently obtained from a "volunteer" seeding than from the regular seeding of a few pounds an 242 BULLETIN No. 394 [//y, acre. On comparatively cheap land available in large areas the advan- tage of a better stand from volunteer seeding may offset the loss of a cropping season that results when sweet clover is allowed to produce seed. FIG. 16. A GOOD JOB OF PLOWING UNDER SWEET CLOVER IN THE FALL OF THE SECOND YEAR An improvised sheet metal attachment in front of the mold board to flatten the sweet clover is a great aid in turning under old sweet clover. Early Spring Plowing Desirable for Green-Manure Crop It was formerly believed that where sweet clover was to be used as a green-manure crop, it should be allowed to grow as late in the spring as possible in order to provide a large amount of organic material to plow under. It has been found, however, that little advantage may be expected from postponing the plowing of sweet clover after it has at- tained a height of 4 to 6 inches. When plowed before it is this high, there is sometimes difficulty in killing it. There are two reasons why late spring plowing has no advantages from the fertility standpoint. In the first place the spring growth of sweet clover is largely a matter of translocation of material from the roots of the plants to the tops, and consequently very little organic matter is added by delaying the spring plowing (see pages 236 and 237). Furthermore since the green material undergoes rapid decay, only a comparatively small portion of it actually remains in the soil a few weeks after plowing. So far as the supply of available nitrogen is con- cerned, there is no advantage in late spring plowing since the amount 1933] SWEET CLOVER IN ILLINOIS 243 supplied at the earlier date is itself in excess of the needs of the crop which follows. In experiments with both dark- and light-colored soils little advan- tage, if any, was obtained by delaying the plowing of sweet clover until it was 15 to 18 inches high over plowing it when it was 4 to 6 inches high. In 1925, a year of low spring rainfall, a decidedly unfavorable effect resulted from late plowing (Table 13). On the Sidell field the TABLE 13. EFFECT OF TIME OF PLOWING UNDER SWEET CLOVER ON YIELD OF CORN, ILLINOIS EXPERIMENT FIELDS Field Kind of soil Number of plots Number of years Corn yield per acre following Early plowing Late plowing Odin Light-colored Dark-colored Dark-colored 6 3 5 14 5 1 4 2 7 1 bu. 33 71 49 59 65 bu. 33 73 50 61 51 Clayton Sidell Sidell Dark-colored yield of corn was 65 bushels on land plowed early in the spring and 51 bushels on late-plowed land. Late sweet clover depleted the soil water supply, resulting in a poor seed bed and an uneven stand of corn. Since timeliness is an important consideration in the growing of all crops, the desirability of plowing sweet clover at least ten days in ad- vance of the date for planting corn cannot be stressed too strongly. Difficulties Encountered With Fall Plowing A few farmers have been impressed unfavorably with sweet clover as a green-manure crop on account of the spring growth encountered where the biennial type is plowed under in the fall of the same year it is seeded. This unfavorable effect is more pronounced in some years than in others. Other farmers have experienced little difficulty with this method of handling. In any event, two considerations the thoro cutting of the sweet-clover roots and a well-turned furrow slice are important in keeping down this spring growth. A few farmers have found that plowing the land less than 5 inches deep is helpful. Fre- quent and thoro disking during the spring following fall plowing also helps to control the growth. Where the land can be kept clean, fall plowing of the first year's growth appears to be satisfactory from the standpoint of corn yields. 244 BULLETIN No. 394 [.July, On the Alhambra experiment field the four-year average yield of corn was 42 bushels an acre on fall-plowed land and 37 bushels where spring plowing was practiced. Effects of Harvesting a Fall Hay Crop As suggested previously, sweet clover frequently produces a satis- factory hay crop when cut in the fall of the first year. However, the earliness of the next year's spring growth, as well as its amount, is affected materially by hay removal. The extent of the influence of hay removal on the following spring's growth is determined by the time of cutting the crop. Willard 15 * found that cutting sweet clover in September reduced the spring growth more than half, whereas a November cutting affected the yield but little, if at all. This difference is due to the fact that the sweet-clover plant stores its food supply for the following year's growth in the roots in TABLE 14. EFFECT ON THE FOLLOWING CORN CROP OF HARVESTING A FALL SWEET-CLOVER HAY CROP, ILLINOIS EXPERIMENT FIELDS Place Number of plots Number of years Yield of corn per acre where Hay was removed No hay was removed Urbana 6 8 3 3 bu. 53 57 58 bu. 55 58 65 Carthage First-year corn the fall. The top is the manufacturing plant and the roots the store- house. When the manufacturing unit is removed by the cutting of the hay, storage ceases and the supply of food for the next year's growth is curtailed. By November the manufacturing process is at a low ebb. The removal of hay at that time, therefore, does not materially affect the storage process and consequently there is no retarding influence upon the spring growth. Willard states that "it is often possible to pasture sweet clover which was not cut in the fall two weeks sooner than that which was cut for hay." 15 * That the value of sweet clover for soil-improvement purposes can- not be judged entirely by the amount of growth or by the nitrogen which it contains, or by consideration of any one factor, is shown again by the negligible effect of hay removal on the yield of first-year corn following sweet clover at Urbana and at Carthage (Table 14). 1933] SWEET CLOVER IN ILLINOIS 245 The second corn crop following hay removal at Carthage showed a marked decrease in yield (Table 14). The value of the sweet-clover hay for feeding purposes, however, is probably great enough to more than compensate for reduced corn yields, particularly if only one corn crop is grown after the sweet clover. Use and Comparative Value of Sweet Clover As a Pasture Crop Altho no definite statistics are available on the percentage of sweet clover that is used for pasture, estimates of Illinois farm advisers indi- cate that on the average 50 to 60 percent of the sweet-clover acreage of the state is pastured to some extent and 10 to 15 percent is saved definitely for grazing the second year. In some regions, because of the nature of the agricultural enterprise, as much as 75 percent of the sweet-clover acreage is used for grazing and 50 percent is grown defi- nitely for this purpose, tho eventually all sweet clover is plowed under for soil improvement. Sweet clover is capable of furnishing more grazing than almost any other common corn-belt pasture plant. On poor soils it has no rival, but on rich soils alfalfa also produces an abundance of forage. Sweet clover has a carrying capacity of one to two animal units an acre in the fall of the first year's growth and one to three animal units an acre during the grazing period of the second year's growth. As an average, the grazing period is about 40 days in the fall of the first year and about 110 days in the second year. The production of milk and meat from animals grazed on sweet clover compares favorably with production from animals grazed on other pasture plants. The large amount of forage available in a sweet- clover pasture during the low production period of most permanent pastures contributes to the value of sweet clover as a pasture plant. Sweet clover is one of the best sources of cheap feed. The success of sweet-clover pastures depends on proper manage- ment. Some farmers find it satisfactory to sow a late-maturing strain of sweet clover in all small grain and then pasture this lightly after the small grain is removed, beginning about the middle of August and con- tinuing until freezing weather. Heavy pasturing of the first year's growth results in considerable winterkilling. Because of the high pro- duction of the second year's growth only enough to meet the needs of the herd should be reserved. The remainder should be plowed up and a cultivated crop planted. Sweet clover should be pastured close the second year to give the best results (Fig. 17). Pasturing of the second year's growth may begin after the plants are 6 to 8 inches high and 246 BULLETIN No. 394 {July, may continue until about the middle of August. Where animals are not able to consume all the forage, the pasture should be mown high in order to stimulate the growth of new shoots. Mowing sweet clover after it begins to bloom is of little value, and unless it is mown high a large percentage of the plants may be killed. 16 * Sweet clover sown alone and in mixtures can be pastured earlier the first year than when sown with a nurse crop. When sown in a blue- FIG. 17. SWEET CLOVER THAT Is Too LARGE FOR BEST PASTURE A large number of livestock must be pastured per acre if sweet clover is to be kept from growing too rank. It may be desirable at times to leave only a portion of a sweet-clover field for pasture, the size of the area depending on the number of animals to be grazed. grass sod*, sweet clover should be pastured the first year only after it has become well established, and then very lightly. Mixed grazing brings about a more uniform and succulent pasture growth than results where only one kind of animal is used. Hogs do well on sweet clover so long as the forage is succulent. Sheep raisers find it superior to other clovers and to bluegrass pasture. For dairy cattle no other corn-belt forage plant produces a better flow of milk. The use of sweet clover alone for beef cattle has been questioned, tho when supplemented with grain 8 * or when grown in mixtures, it gives good results. Oats and sweet clover in a mixture have given satisfac- tory gains for beef cattle. Horses and mules eat sweet clover readily and seem to do well on it. Problems in Pasturing Sweet Clover The prevention of bloat is one of the first problems in pasturing animals on sweet clover, as it is in pasturing them on any legume. Tho 1933] SWEET CLOVER IN ILLINOIS 247 there is less danger of cattle becoming bloated from sweet clover than from the common pasture legumes, it is well to take certain preventive measures. Among young stock bloat is most likely to occur during the early grazing period. To avoid bloat animals should be given a full feed before they are turned onto sweet clover, and they should be kept in the pasture once they have started grazing. Water, minerals, and roughage, such as hay or straw, should be available at all times. Sweet clover of the first year's growth is relished by all classes of livestock tho occasionally it is necessary to develop a liking for it in individual animals by proper pasture management. Animals once accustomed to young sweet clover often prefer it to other so-called more palatable legumes. When the second year's growth approaches maturity it becomes woody and acquires a bitter taste that animals do not like. Where the second year's growth matures before the first year's growth is large enough to pasture, the difficulty can be solved by using a late-maturing strain of sweet clover, by providing a large acreage of the first year's growth, by supplementing the sweet-clover pasture dur- ing this period with a crop like Sudan grass, or by encouraging new growth by mowing the clover before there is any sign of blooming. By a wise choice of varieties, adherence to proven cultural prac- tices, and proper pasture management, these problems in regard to pasturing, as well as other general pasture problems, can be solved satisfactorily. Place of Sweet Clover in the Rotation No definite statement can be made as to the best place for sweet clover in the rotation. The importance of corn and its ability to utilize the large quantities of plant- food elements supplied by the sweet clover make it the logical crop to follow sweet clover. In case the soil is low in available nitrogen, one or two crops of sweet clover may be followed to advantage with winter wheat or spring grains such as spring wheat, oats, or barley. Such a plan cannot be practiced continuously in any one field, however, because of the tendency of the small grains to lodge with the repeated growing of sweet clover. The lodging is a result of the formation of an excessive amount of nitrate-nitrogen. Where alfalfa is to be grown on land that is in a rundown condi- tion, sweet clover may well precede the alfalfa crop. Three consider- ations commend this practice: (1) if the sweet clover grows well, it is certain that the soil is not too sour to grow alfalfa; (2) since both of these crops are infected by the same nodule bacteria, the sweet clover will aid in establishing a good flora of nodule organisms for the 248 BULLETIN No. 394 Uly, alfalfa; and (3) the decaying sweet clover will furnish a supply of available food material to start the alfalfa in a flourishing condition. It is important in such practice to plow under the sweet clover early enough to prevent excessive loss of water by transpiration and to allow the sweet clover to decay before sowing the alfalfa. Sweet clover should be plowed under in May or early June for an August seeding of alfalfa or in October or November for a spring seeding. Clipping Sweet Clover Unlike red clover, sweet clover should not be clipped in the fall of the first year, since clipping at this time reduces the amount of organic material and nitrogen to be returned to the soil and at the same time increases the hazard of winterkilling thru heaving. Close clipping is more detrimental than clipping high. Pasturing has practically the same effect as clipping. The greatest injury is caused by clipping sweet clover from the middle of August to the middle of September. Clipping sweet clover in the spring is practiced to reduce top growth and thereby make seed harvesting easier. 17 * Spring clipping is believed to bring about a more uniform blooming of the plants and ripening of the seed. Experiments at the Illinois Station show that spring clipping to be most effective, and at the same time not kill the plants, should be made before the plants come into bloom and when the stubble contains some branches or stem buds. Sweet clover clipped on May 23 leaving the stubble 6 inches high suffered a 50-percent kill- ing; where it was 8 inches high, 33 percent was killed; and where it was 10 inches high, only 20 percent was killed. Harvesting Sweet-Clover Hay Nearly 10 percent of the acreage of sweet clover sown in Illinois is harvested for hay, and the average annual yield is 1^4 tons an acre. The quality and yield of hay varies markedly depending on the time of harvest. Excellent Hay Obtained From First Year's Growth. Excellent hay is often cut in the fall from the first year's growth. This hay is fine stemmed, leafy, and very palatable. The yields are also good. Over a period of three years the average yield of hay at the Urbana experi- ment field was 1.84 tons an acre (Table 15). Fall cutting reduced the yield of the spring hay crop (Table 16). In the Illinois experiments sweet clover was seeded in early oats and after the grain was harvested the clover was permitted to grow until late in the season, when it was harvested by mowing close to the ground. 1933] SWEET CLOVER IN ILLINOIS 249 The time of cutting sweet clover is important. Sweet clover makes a rapid root growth during the month of September by storing food reserves in the roots. If hay is harvested before the movement of ma- terials has progressed far enough to insure cold resistance, a high per- centage of heaving and winter injury is likely to result (see page 244). TABLE 15. ACRE- YIELDS OF SWEET-CLOVER HAY AT END OF FIRST YEAR'S GROWTH, URBANA EXPERIMENT FIELD Year Date cut Yield 1920 tons 1 65 1921 October 10 2 48 1922 October . . 1.38 Three-year average . ... 1.84 TABLE 16. ACRE- YIELDS OF SWEET-CLOVER HAY WHEN HARVESTED IN FALL OF FIRST YEAR AND IN SPRING OF SECOND YEAR COMPARED WITH SPRING OF SECOND YEAR ONLY, URBANA EXPERIMENT FIELD Year and number of cuttings Fall of first year Spring of second year Total 1920-21 Two cuttings . . tons 1.65 tons .35 tons 2.00 One cutting 2.86 2.86 1921-22 Two cuttings 2.48 1.42 3.90 2 50 2.50 Harvesting Second Year's Growth a Doubtful Practice. The har- vesting of sweet clover for hay during the second year of its growth has many attendant problems. First, it is difficult to harvest the hay without killing a high percentage of the plants. This fact is shown by experiments at the Illinois Station in which the first harvest of sweet clover was made when the plants were 33 inches tall and the last when they were 42 inches tall. The greatest loss came when the plants were the largest and the least when they were the smallest. Where the clover was cut leaving a 10-inch stubble, less injury resulted than when the plants were cut to 6 or 8 inches, but the hay yields were reduced materially (Table 17). Where the sweet clover was cut low, it was entirely killed. Cutting 10 inches high left twice as many buds on the stubble to start new growth as cutting 6 inches high. Likewise cutting on May 23 resulted in twice as many buds on the stubble as cutting on June 1. The thicker the stand, the higher the 250 BULLETIN No. 394 buds occur and the higher the plants should be mowed to prevent their being killed. Obviously to mow the plants high at an early stage of growth will give only a small amount of hay which may not pay for the difficulty of gathering it. If a stand of sweet clover is not to be maintained, the hay crop can be mowed close to the ground. The best time to harvest, all things con- TABLE 17. EFFECT OF HEIGHT OF CUTTING SWEET CLOVER ON YIELD OF HAY, URBANA EXPERIMENT FIELD Year Date of cutting Acre-yields when cut at 6 inches 8 inches 10 inches 1917 May 23 May 23 May 17 May 29 tons .78 1.29 .91 .36 .835 tons .57 1.01 .46 .21 .562 tons .48 1.02 .47 .21 .545 1918 1919 . . 1920 Four-year average TABLE 18. EFFECT OF DATE OF CUTTING ON ACRE -YIELDS OF SWEET CLOVER, URBANA EXPERIMENT FIELD Year and date of cutting Yield Year and date of cutting Yield 1917 May 23 tons .48 1919 May 17 tons .47 May 26 72 May 26 .66 May 29 .... .... .78 June 2 1.00 June 1 1.03 June 7 1.51 1920 May 29 .21 1918 June 8 1.09 May 23 1.02 June 15 . 1.43 May 27 1.18 May 29 1.56 1921 June 3 1.27 June 6 .35 June 7 1 43 1.00 July 9 1.38 sidered, is just before the plants come into bloom. A few days' delay in the time of cutting increases the yield materially (Table 18). In making sweet-clover hay from the second year's growth it is difficult to cure the large succulent plants completely if the weather is unfavorable for haymaking. Early cutting increases this difficulty and late cutting reduces the palatability of the hay by increasing the per- centage of coarse stems (Table 19). Danger From Incomplete Curing. Moldy sweet-clover hay results from incomplete curing. Such hay fed to stock may produce a disease known as "sweet-clover poisoning." 11 * The blood of the affected 1933] SWEET CLOVER IN ILLINOIS 251 TABLE 19. EFFECT OF DATE AND HEIGHT OF CUTTING ON PERCENTAGE OF COARSE STEMS, FINE STEMS, AND LEAVES OF SWEET-CLOVER HAY, URBANA EXPERIMENT FIELD Date and height of cutting (1917) Percentage composition of plants Coarse stems Fine stems Leaves May 23 6 inches 45.87 42.58 41.43 53.63 48.03 45.94 51.98 50.40 46.82 61.69 58.39 56.67 28.58 9.36 8.43 5.83 6.46 6.39 7.59 6.88 6.98 5.86 4.21 5.93 7.21 14.30 44.76 48.84 52.72 39.90 45.71 46.50 39.27 42.61 47.24 34.11 35.68 36.13 57.18 8 inches 10 inches May 26 10 inches May 29 6 inches 8 inches 10 inches June? 6 inches 8 inches 10 inches July 7* 1 1 inches Second cutting. animal loses the ability to clot, and without showing any external symptoms, unless the animal is injured, the disease progresses until internal hemorrhages cause death. The disease is confined almost en- tirely to cattle and especially to young stock. No way has yet been found to determine by inspection hay that will cause the disease. Suspected hay can be tested, however, by being fed to rabbits at the same time that it is fed to cattle. The rabbits will die before the cattle are seriously injured. Moldy hay can be fed to animals that are known to be resistant to the disease or it can be fed in small amounts with good hay. Harvesting the Seed The rapid increase in the acreage of sweet clover in Illinois is due to its popularity as a pasture crop and as a soil builder. Its use for Less than 2 percent of the sweet-clover acreage sown is finally har- seed production and as a hay crop are of minor importance (Table 20). vested for seed, yet the average seed production in Illinois, 48,250 bushels, is 5.2 percent of the seed produced in this country (Table 21). While the average acre-yield of sweet-clover seed in Illinois 3.45 bushels (207 pounds) is not quite so high as the yield in the states to the northwest and west of Illinois, yet the higher price per bushel 252 BULLETIN No. 394 makes the gross acre-value the highest of that of any important sweet- clover state. The harvesting of sweet-clover seed in Illinois has not been prac- ticed extensively, owing partly to the fact that the region to the north- west, including North Dakota, South Dakota, Minnesota, and Ne- braska, seems to be better adapted for seed production. With cheaper TABLE 20. SWEET-CLOVER SEED AND HAY PRODUCTION IN ILLINOIS, 1925-1932" Seed Hay Year Acreage Yield per acre Production Acreage Yield per acre Production 1925 acres 7 000 bu. 4.0 bu. 28 000 acres 40 000 tons 1.20 tons 48 000 1926 15 000 4.0 60 000 45 000 1.20 54 000 1927 20 000 3 7 74 000 50 000 1 60 80 000 1928 13 000 4.0 52 000 38 000 1.70 65 000 1929 17 000 3.5 59 500 30 000 1.75 52 000 1930 14 000 3.3 46 200 22 000 1.20 26 000 1931. . 13 000 2 6 33 800 18 000 1 60 29 000 1932 13 000 2.5 32 500 20 000 1'50 30 000 Eight-year average . . 14 000 3.45 48 250 32 875 1.47 48 000 These data were furnished by A. J. Surratt, Agricultural Statistician, U. S. Department of Agriculture cooperating with Illinois Department of Agriculture. TABLE 21. UNITED STATES PRODUCTION AND IMPORTATION OF SWEET-CLOVER SEED, 1925-1932" Year Production Importation Total 1925... Ibs. 63 534 000 Ibs. 3 544 900 Ibs. 67 078 900 1926 68 406 000 6 381 200 74 787 200 1927 73 428 000 4 304 300 77 732 300 1928 54 564 000 3 495 200 58 059 200 1929 52 062 000 1 492 700 53 554 700 1930 50 898 000 209 000 51 107 000 1931 50 262 000 50 262 000 1932 34 356 000 34 356 000 55 938 750 2 428 413 58 367 163 NOTE. No sweet-clover seed has been imported into the United States for the fiscal year end- ing June 30, 1933. Compiled from statistics of the U. S. Department of Agriculture, Bureau of Agricultural Eco- nomics. seed prices the harvesting of sweet-clover seed from cheaper land be- came more prevalent. It is now a question whether the northern regions with their short seasons can produce seed of the medium and late strains. Because of decreased land values in Illinois, the relatively high gross acre-value of sweet-clover seed in the state, the demand for seed of the later strains, and the desire to secure seed of pure strains free from certain weed seeds, seed production on some of the cheaper lands of Illinois may be advisable. 1933] SWEET CLOVER IN ILLINOIS 253 Because of the uneven ripening and shattering of seed and the large size of the plants, no thoroly satisfactory method has been worked out for harvesting sweet-clover seed. The time of harvesting will depend on the method used. In general, harvesting should start before serious shattering begins, even tho some green seeds and flowers may still be present. If methods which involve considerable handling of the seed are used, the crop must be cut when somewhat immature and the oper- ations carried on while the plants are damp with dew or rain. The crop may be cut with a grain binder or corn harvester, then shocked and threshed like small grain, tho there is great loss thru shattering by this method. Adjustment of concaves, riddles, and the speed of the fan are necessary to hull any large percentage of the seed. If a binder is used, shattering losses can be partially overcome by at- taching a box beneath the platform of the binder at the junction of the platform and the elevator and another below the outer extremity of the binder deck, thus saving 15 to 20 percent of the seed. After the seed is threshed, it may be cleaned further by the use of a clover huller, a scarifier, and a fanning mill. The above method of harvesting is wasteful and expensive, but has the advantage of using equipment which is common in grain harvest- ing. The clover huller is not well adapted to the threshing of sweet clover, principally because of the difficulty of feeding the large plants thru the machine. A sweet-clover seed harvester designed to beat off the seed in the field has been used to some extent in this state. It is a homemade machine built from an old grain binder and has a screened-in platform and a heavy reel driven directly from the bull wheel (Fig. 18). As the machine is drawn thru the field, the seeds are beaten off on the screened platform. Some green seeds, stems, and leaves, as well as insects, accompany the ripe seed. This material is removed from the platform, dried, and then threshed. This harvester has the advantages of being cheap, easy to construct, and inexpensive to operate. All the sweet-clover straw remains in the field to be plowed under for manure. Some believe that harvesting with this machine tends to increase the uniformity in a strain of sweet clover. The disadvantages of such a machine as described above are that (1) much of the seed is shattered on the ground when hit by the reel, tho probably not so much as is lost when harvested with a grain binder ; (2) the material harvested contains a high percentage of moisture be- cause of green seeds and foreign material and will heat readily if not cured properly; (3) the seed is not easily removed from the platform 254 BULLETIN No. 394 [July, because of the construction of the machine ; and (4) it is still neces- sary to hull and clean the seed after it is gathered by this method. More recently the combine-harvester has come to be used for har- vesting sweet-clover seed, and from the few observations made of this method it appears to be successful, causing only a small amount of FIG. 18. A SWEET-CLOVER HARVESTER MADE FROM AN OLD GRAIN BINDER The seeds are beaten onto a screened platform by a heavy reel driven directly from the bull wheel. shattering. Because of the high cost of combine-harvesters, however, only a few farms have them at present. The seed as it comes from the combine is fairly clean but only partially hulled. This method of harvesting like the others, requires another machine to complete the hulling process. A combine can be used effectively in harvesting seed from large plants while they are still tough from rain, but this seed must be dried carefully because of excess moisture. Much labor and care are necessary in drying all combine- harvested seed in order to avoid heating. When a combine-harvester is used, all the straw is left in the field to be plowed under. With a heavy growth of sweet clover these ma- chines are not able to take a full swath. Sweet Clover Has Merit As Bee Pasture As a honey plant the merit of sweet clover has long been recog- nized. Sweet clover was sown along roadsides and in waste places as a honey plant before it was used extensively as a cultivated crop. The production of honey from sweet clover is not only large but the quality 1933] SWEET CLOVER IN ILLINOIS 255 is high. Sweet clover normally blooms after white and alsike clover and thus meets a definite need for bee pasture. By mixing strains of sweet clover which bloom at different dates, the period over which sweet clover will furnish nectar can be extended greatly. In order to maintain pure varieties, seed from mixed strains should not be harvested and offered for sale. CULTURE OF SWEET CLOVER In some respects the culture of sweet clover is less difficult than that of the other common legumes. It is considered easier to secure and maintain a stand of sweet clover but more difficult to harvest the seed or hay. Sweet clover is usually grown in the small grains much the same as is red clover. 2 * Occasionally, however, it is sown in a cul- tivated crop such as corn and sorghums, or sown alone in late summer as is alfalfa. It is also sown on permanent pastures and in pasture and hay mixtures. Time of Seeding About 75 percent of the sweet clover grown is sown at the time of seeding the spring grain. 2 * Where the sweet clover will grow too large and interfere with the harvesting of the grain crop, the seed may be sown ten days to three weeks later than the spring grain. When sown in winter grain, sweet clover should be seeded the latter part of February or the first part of March in southern Illinois, and the latter part of March or the first part of April in northern Illinois. The importance of early seeding is shown by the results from the Virginia Agricultural Experiment Station, 19 * where the highest yield of clover was secured by seeding on February 15 altho seeding on March 1 also gave good yields. This region is located in the same latitude as the extreme southern portion of Illinois. Early seeding gives the clover an opportunity to germinate and grow as soon as the winter grain starts its spring growth. If the sweet clover is sown too late, it is often smothered out by the grain crop. With early seeding, however, there is always danger of the clover seeds germinating with the first period of warm weather and later being killed by a hard freeze. Experiments conducted at the Illinois Station with sweet clover seeded in cultivated crops such as corn show that when sweet clover was sown in the corn after the last normal cultivation, the chance of getting a stand was not very good. In more recent experiments sweet clover has been seeded earlier in the corn crop by allowing the last cultivation to come at an earlier date. 256 BULLETIN No. 394 [July, When farm practice makes it desirable, sweet clover may be seeded alone any time between early spring and late summer as one would seed alfalfa, if the land is free from weeds. Seeding six weeks to two months before killing frosts is recommended to insure sufficient growth to prevent winterkilling. Occasionally sweet clover is seeded in permanent bluegrass pasture in late winter or early spring, depending on the preparation of the seed bed necessary to put the seed in contact with the soil. 4 * When used in mixtures, sweet clover is seeded at the time the mixture is sown, which is usually in early spring or late summer so that early growth takes place during the cool season. Method of Seeding Sweet clover is usually seeded on winter grain by broadcasting. Now arid then it is seeded on winter grain with a grass seed drill, but if conclusions can be drawn from experiments with red clover, broad- casting is apparently about as good as drilling where the seed will be covered by freezing and thawing. Where sweet clover is seeded somewhat later than the spring grain in order to prevent its interference when the grain is harvested or where the spring grain is broadcasted, the sweet-clover seed is broad- casted. If the spring grain is drilled, sweet clover is usually seeded from the grass seed attachment of the grain drill at the same time. When grown in corn, sweet clover is usually broadcasted either before or after the last cultivation of the corn. If sown before, shallow cultivation is recommended in order to avoid covering the seed too deeply. When the seed is sown following the last cultivation, usually no effort is made to cover it, tho it may be covered by drawing a light harrow or some other implement between the cultivated rows. Occa- sionally sweet clover is seeded with a one-horse grain drill. Drilling with a disk drill is often recommended for seeding sweet clover in bluegrass sod in order to bring the seed in contact with the soil. When used in mixtures, sweet-clover seed may be drilled or broadcast, depending on the mixture, the time of seeding, and the prep- aration of the seed bed. Rate of Seeding The rate of seeding sweet clover may be varied considerably. Ordi- narily from 10 to 15 pounds an acre of hulled scarified seed is the maximum amount to sow. In Illinois experiments where 5, 15, and 30 pounds of seed to the acre were used, all amounts gave good stands. If unhulled seed is used when sowing sweet clover on winter grain J9JJ] SWEET CLOVER IN ILLINOIS 257 or on permanent bluegrass pastures, the rate of seeding should be in- creased to 20 or 25 pounds an acre. Unhulled sweet-clover seed, be- cause of hulls and other foreign material, weighs only about 33 pounds to the bushel. In the Virginia experiments the unhulled seed sown on winter grain yielded considerably better than the hulled scarified seed regardless of the time of seeding. 19 * Where sweet clover is to be seeded after the FIG. 19. SPOTTED STAND OF SWEET CLOVER THE RESULT OF OATS LODGING A poor stand of sweet clover is often caused by a heavy grain crop that deprives the clover seedlings of the necessary moisture and plant-food materials or that shades and smothers them. action of freezing is over, the scarified seed is usually recommended. The unscarified seed may not germinate well because the seeds are un- able to take up moisture thru their hard seed coats. Scarifying will frequently double the germination of such seeds. When sown during freezing weather, the action of frost increases the germination of the unhulled or unscarified seed. Nurse Crops The kind of nurse crop to use is not so important a question with sweet clover as it is with red clover and alfalfa. Sweet clover is a more vigorous crop and is better able to compete successfully with the grain crops. Barley is probably the best nurse crop for sweet clover, but early oats and spring wheat are also very good. Under normal conditions good stands of sweet clover can be secured in late oats. Where there is difficulty in securing a stand because of the rank growth of the nurse crop, a lighter seeding of the grain crop is recommended (Fig. 19). 258 BULLETIN No. 394 Winter wheat is a good nurse crop for sweet clover when the clover is seeded sufficiently early to compete with the grain plants. Winter rye usually makes the poorest nurse crop for clovers of any of the small grains. Where the rainfall is not sufficient for success with a nurse crop, sweet clover can be seeded like alfalfa in late summer without a nurse crop. SWEET-CLOVER DISEASES 4 Mosaic Mosaic disease is common thruout Illinois, more than half the plants in a field often showing distinct symptoms of it. The disease is easily iden- tified by a light green mottling of the leaves alternating with the normal green color. The pattern is rather small and irregular. Altho many clover plants infected with mosaic disease seem to attain normal size, a considerable number usually are more or less stunted in growth so that there is little doubt that the disease causes considerable loss. The disease is caused by a virus, an organic entity much smaller in size than bacteria. In some crops mosaic diseases are carried in the seed. In the field they are usually carried from plant to plant by certain insects. The sweet-clover mosaic has not yet received much study and prac- tically nothing is known concerning its control. Root Rot During the spring sweet-clover plants are occasionally found dying in fields that had appeared healthy the previous fall. Close examination re- veals that the crown and roots of the plants are entirely rotted. In the vicinity of the dead plants other plants occur that appear unthrifty and that show a definite decay of the roots. This root disease has been ob- served in Illinois during the last seven years and is apparently becoming more common. Some fields have been injured so severely that they have been plowed in early June and planted to another crop. This disease appears to be of a parasitic nature but the cause has not yet been definitely determined. Breeding experiments with sweet clover are showing striking differences in resistance and susceptibility of sweet- clover plants to the disease, and it seems probable that control will ulti- mately be effected thru the use of resistant strains. Other Diseases Several different kinds of leaf spots are known to occur on sweet clover, but none of them has been observed to cause any considerable loss in Illinois. Black-stem disease has frequently been observed and sometimes ap- pears to cause considerable injury. The stems are blackest on the lower This section was prepared by Benjamin Koehler, Associate Chief in Crop Pathology. 1933] SWEET CLOVER IN ILLINOIS 259 portion, and some black streaks may occur as far as three- fourths of the way up the stem. The cause and control of this disease have not been de- termined. INSECTS AFFECTING SWEET CLOVER a There are a large number of insects that may be observed at one time or another on the sweet-clover plant, but none of them is known to damage it severely in Illinois. A few of the insects that feed on the plant, tho they have not been known to cause any economic damage to the crop, are listed below. Clover Leaf Weevil (Hypera punctata Fab.) Early in the spring the leaves of sweet clover are sometimes found with small holes in them or small portions of the edges eaten. This con- dition is especially common where sweet clover is grown in a mixture with red clover. It is caused by tfu feeding of the larvae of the clover leaf weevil. This weevil does not commonly cause serious damage, as the plant rapidly outgrows the attack. No cases of destruction of the sweet-clover crop by this weevil are known. Grasshoppers (Locustidae) During the summer and fall, grasshoppers frequently feed on the leaves of the sweet-clover plant, causing them to have a ragged appearance. The attack is not serious and there are no records of real economic damage to sweet clover by grasshoppers under Illinois conditions. Grape Colaspis (Colaspis brunnea Fab.) Larvae of the grape colaspis have been found feeding on the roots of sweet clover. They feed on the surface of the main root and to some extent on the small roots, but their feeding has not been found to affect the growth of the plant. They cannot be considered a serious pest of the crop. Clover Stem Borer (Languria mozardi Latr.) During the middle of the second summer of sweet-clover growth, the larvae of the clover stem borer can ordinarily be found tunneling in the stems of the plants. Records show that 40 to 50 percent of the stems in a field may be infested. Even under these conditions it is impossible to determine this infestation by casual observation. At a distance of 4 to 5 feet, the infested stems cannot be distinguished from adjoining uninfested stems. The plant is evidently able to sustain its own growth and support the insect at the same time. 'This section was prepared by J. H. Bigger, Entomologist, Illinois State Natural History Survey. 260 BULLETIN No. 394 [July, SUMMARY Sweet clover ranks first in acreage among the legumes in Illinois, the farm area planted to this crop having increased from 48,000 acres in 1919 to 850,000 acres in 1932. For soil improvement purposes, sweet clover has no superior among the legumes. In fields where sweet clover has been grown, not only is the first succeeding crop larger but yields from subsequent crops are increased. The favorable effect of sweet clover upon the soil results from a combination of factors, in- cluding improved soil tilth, nitrogen fixation, addition of active organic matter to the soil, increase in the microorganic life of the soil, and a gain in available plant nutrients. A large proportion of Illinois farmers use sweet clover for both pasture and soil improvement and probably for many farmers there is no better way of utilizing the crop. In some parts of the state, because of the nature of the agricultural enterprise, as much as 75 percent of the sweet-clover acreage is used for grazing and 50 percent is grown definitely for this purpose, tho eventually all sweet clover is plowed under for soil improvement. Sweet clover is capable of furnishing more grazing than almost any other common corn-belt pasture plant. On poor soils it has no rival but on rich soils alfalfa also produces an abundance of forage. There is less danger of cattle becoming bloated from sweet clover than from the common pasture legumes. Good yields of excellent sweet-clover hay are often secured in the fall of the first year's growth. The harvesting of sweet clover for hay during the second year of its growth is frequently unsatisfactory. This hay is not only coarse and stemmy but has occasionally been known to poison livestock. Less than 2 percent of the sweet-clover acreage in Illinois is finally harvested for seed, altho the average acre-yield is about 3 1/2 bushels. Several methods of harvesting sweet-clover seed in Illinois have been used but no thoroly satisfactory method has yet been worked out. The culture of sweet clover is less difficult than that of the other common legumes. Most of the sweet clover grown is sown at the time of seeding spring grain. The usual dates of seeding are the latter part of February and the first part of March in southern Illinois, and the latter part of March and the first of April in northern Illinois. Early seeding is important. Unhulled seed may be sown in wheat as early as December. The practice of sowing sweet clover in corn at the last cultivation is frequently unsuccessful, seasonal conditions materially affecting the results obtained. Barley is probably the best nurse crop 1933] SWEET CLOVER IN ILLINOIS 261 for sweet clover, but early oats and spring wheat are also very good. Winter rye usually makes the poorest nurse crop of any of the small grains. Sweet clover thrives under a wide range of climatic and soil con- ditions, and when properly inoculated, it will grow in practically any nonacid soil in Illinois. Like alfalfa, sweet clover is not a successful crop if suitable nodule bacteria are absent. Unless one of these crops has been grown on the land previously, inoculation is highly important. Most Illinois soils lack bacteria that form nodules on and fix nitrogen in the sweet-clover plant. Manure is a valuable aid in securing a stand of sweet clover, particularly on recently limed land. Sweet clover seldom grows satisfactorily on sour soils and to sow it on such soil is to invite failure. Phosphorus as well as potassium can be used with profit on many soils before sweet clover seed is planted. The effective- ness of sweet clover as a green-manure crop is also frequently im- proved by the use of potassium-containing fertilizers. Unless needed for pasture it is ordinarily advisable to plow sweet clover under when green. When it is allowed to grow during the sec- ond season, a loss of land for the cropping season results, and con- siderable difficulty in plowing under the dead material is encountered. Sweet clover may be plowed in the spring of the second season's growth when it is 4 to 6 inches high. Postponing the date of plowing has little to recommend it and may have some disadvantages, tho earlier plowing may fail to kill the sweet clover. Plowing in the fall of the first year may have undesirable results owing to the difficulty encountered in killing the spring growth during seed-bed preparation. However, a few farmers have found fall plowing satisfactory. Sweet clover may be pastured lightly in the fall, but heavy pasturing of the first year's growth results in considerable winterkilling. Close pasturing during the second year gives satisfactory results. Sweet clover may be pastured after it is 8 inches high. Sweet-clover varieties and strains are being developed and adapted to almost every condition and use. Of the more than 25 known species of sweet clover grown in various parts of the world, over half have been tried out in the United States. The biennial white-flowered sweet clover, Melilotus alba, is the most important and constitutes more than 80 percent of all the sweet clover grown in the corn belt. The superior value of sweet clover for soil-improvement purposes and as a pasture crop has been proved by field experiments and demon- strated by the experiences of farmers, not only in Illinois but in sur- rounding states. 262 BULLETIN No. 394 LITERATURE CITED 1. BRAY, R. H. A field test for available phosphorus in soils. 111. Agr. Exp. Sta. Bui. 337. 1929. 2. CROSBY, M. A., and KEPHART, L. W. Sweetclover in corn belt farming. U. S. Dept. Agr. Farmers' Bui. 1653. 1931. 3. ELDERS, A. T. Some pollination and cytological studies of sweet clover. Sci. Agr. 6, 360. 1926. 4. GRABER, L. F. Improvement of permanent bluegrass pastures with sweet clover. Wis. Agr. Exp. Sta. Bui. 396. Ann. Rpt. of Director, 1926-27. p. 77. 1927. 5. LINSLEY, C. M., and BAUER, F. C. Test your soil for acidity. 111. Agr. Exp. Sta. Cir. 346. 1929. 6. LLOYD, W. A. Sweet clover (Melilotus). A field survey of its distribution, soil adaptation, habits and agricultural value. Ohio Agr. Exp. Sta. Bui. 244. 1912. 7. MILLER, L. B. Extension Messenger, 111. Agr. Ext. Serv. 13, No. 45. 1930. 8. MORTIMER, G. B., and RUPEL, I. W. Sweet clover makes poor showing with dairy heifers. Wis. Agr. Exp. Sta. Bui. 410. Ann. Rpt. of Director, 1928- 29. pp. 82, 83. 1930. 9. PIETERS, A. J. Green manuring. John Wiley & Sons, New York. p. 205. 1927. 10. and KEPHART, L. W. Annual white sweet clover and strains of the biennial form. U. S. Dept. Agr. Dept. Cir. 169. 1921. 11. RODERICK, L. M., and SCHALK, A. F. Studies on sweet clover disease. N. Dak. Agr. Exp. Sta. Bui. 250. 1931. 12. SNIDER, H. J., and HEIN, M. A. The nitrogen and dry matter content of sweet clover tops and roots at various stages of growth. Jour. Amer. Soc. Agron. 18, 273. 1926. 13. STEVENS, O. A., and LONG, H. D. Sweet clover seed studies. N. Dak. Agr. Exp. Sta. Bui. 197. 1926. 14. WILKINS, F. S. Hubam clover. Iowa Agr. Exp. Sta. Cir. 76. 1922. 15. WILLARD, C. J. An experimental study of sweet clover. Ohio Agr. Exp. Sta. Bui. 405. 1927. 16. Sweet clover The effect of cutting the first year on the value for pasture and soil improvement the next year. Ohio Agr. Exp. Sta. Bimonthly Bui. 12, 107. 1927. 17. Clipping sweet clover intended for seed. Ohio Agr. Exp. Sta. Bui. 446, 48th Ann. Rpt., p. 42. 1930. 18. and THATCHER, L. E. Experiments with Hubam clover. Ohio Agr. Exp. Sta. Monthly Bui. 7, 3. 1922. 19. WOLFE, T. K., and KIPPS, M. S. Comparative value of scarified and of un- hulled seed of biennial white sweet clover for hay production. Jour. Amer. Soc. Agron. 18, 1127. 1926. UNIVERSITY OF ILLINOIS-URBANA