Mineral Nutrition Of Soybeans

MINERAL NUTRITION OF SOYBEANS A. J. Ohlrogge Agronomy Department, Purdue University, Lafayette, Indiana

I. Introduction ................................................. 11. Growth Analysis ............................................. 111. Nitrogen .................................................... A. Concentrations in the Plant ................................ B. Rate of Uptake ........................................... C. Redistribution ........................................... D. Fertilization ............................................. IV. Phosphorus .................................................. A. Concentrations in the Plant ................................ B. Rate of Uptake ........................... ............ C. Translocation ............................. ............ D. Fertilization . . . . . . . . . . ............................... V. Potassium . . . . . . . . . . . . . . . A. Concentrations in the Plant ......................... B. Rate of Uptake . . . . . . ..................... C. Translocation . . . . . . . . D. Fertilization . . . . . . . . . VI. Calcium ................ A. Concentrations in the Plant ................................ B. Rate of Uptake, Redistribution, and Fertilization . . . . . . . . . . . . . . . VII. Magnesium .......................................... A. Concentrations in the Plant ......................... B. Rate of Uptake, Redistribution, and Fertilization . . . . . . . . . . . . . . . VIII. SuIfur . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IX. Iron ...................... ............................ A. Introduction ............................................. B. Concentrations in the Plant .................... C. Rate of Uptake, Redistribution and Fertilization . . . . . . X. Manganese . . . . . . . . . . . . . . . . . ................... A. Concentrations in the Plant ......................... B. Rate of Uptake, Redistribution, and Fertilization . . . . . XI. Boron ............................................. XII. zinc .......................... ........... XIII. Copper and Other Elements . . . . . . . . . . . ........... XIV. The Future of Soybean Nutrition . . . . . . ........... References . . . . . . . . . . . . . . . . . . ........... 229

Page 230 231 232 232 233 234 234 236 236 238 239 240 241 244

245 247 250 251 252 252

257 258 258 261

230

A. J. OHLROGGE

1.

Introduction

It is widely recognized that soybean response to direct fertilization is inconsistent. The United States average yield per acre for soybeans during the last twenty years shows little change, in sharp contrast to the remarkable increase in the average acre yield of corn, a competitive crop for the farmer’s intertilled crop acreage. Recognition of this situation motivated the National Soybean Crop Improvement Council to request the authors of this and the following chapter to prepare a critical review of the recent literature on the mineral nutrition and physiology of the soybean. The mineral nutrition paper is restricted to the accumulation and redistribution of the mineral nutrients. Mechanisms of ion uptake are not discussed, since they are not unique for soybeans, and excellent recent reviews are available in the literature. Likewise mineral nutrient functions and interrelationships are discussed in detail only where they have been extensively studied in soybeans. Many hundreds of field fertilization trials are reported in the literature. Only a few of these are discussed because most experiments, on the basis of the information reported in the papers, bring little understanding to the soybean problem. Diagnosis of the mineral nutrition problem of soybeans would be facilitated by knowing the cardinal concentrations in the total plant and plant parts which define and separate deficiency, adequacy, and luxury levels of nutrition. Also uptake rates and the translocation of nutrients within the plant is prerequisite information for understanding nutrition problems. In spite of the recognition of these facts by agronomists and plant nutritionists, these values and related information are most incomplete for soybeans and many other crops. Very little soybean literature is directed toward supplying these data. It was believed, however, that sufficient analyses and data exist in the literature to suggest approximate values. The writer has endeavored to extract these, even though the original research was not intended to be used in this manner. In so doing the writer may infer a conclusion on the part of the original authors which is really that of the writer or his agronomist friends with whom he has discussed the soybean fertility problem. On this point, he asks their indulgence. Each nutrient is discussed separately under the subtitles of nutrient contents in the plant at various stages of growth, uptake rate, translocation, and fertilization. These discussions are preceded by a brief section on the significance of growth analysis and the paper is concluded with a look into the future. This is done by an appraisal of the yield trends of

MINERAL NUTRITION OF SOYBEANS

231

corn and soybeans, and by suggesting possible research areas which may prove most productive in elucidating the unresponsiveness of soybeans to direct fertilization. The paper was prepared in part while the writer was a National Science Foundation postdoctoral fellow at the University of California at Davis. It is a pleasure to acknowledge this splendid program, and to express thanks for the many constructive suggestions of my professional friends who reviewed the preliminary draft of this paper. They are: K. C. Berger, C. H. Black, A. C. Caldwell, E. Epstein, H. J. Mederski, G. D. Scarseth, S. L. Tisdale, together with many of my former graduate students. II. Growth Analysis The dry matter accumulation process of field-grown plants has been characterized through growth analysis. These studies are most numerous in the United Kingdom, but soybeans have not been one of the many species analyzed, since they are not widely grown in these countries ( Blackman and Black, 1959; Watson et al., 1958). Net assimilation rates (N.A.R.) based on leaf area, dry weight, protein and chlorophyll contents have been measured for many species; here again, very few data exist for soybeans. The importance of leaf area in determining yield has been much discussed; however, recent work points up the limitations of total leaf-area measurements (Watson et aZ., 1958). This work showed that 30 per cent of the total dry weight of barley grain was derived from photosynthate of inflorescent origin and an additional 20 per cent was the product of the flag leaf. The defoliation studies from Iowa suggest a similar relationship for soybeans; 50 per cent defoliation at a stage where very little regrowth occurs resulted consistently in only 10 to 20 per cent decreases in grain yield (Camery and Weber, 1953). Complete defoliation caused 85 per cent decrease in grain yield at a level of 28.9 bushels per acre. More recently Weber (1955) completely defoliated beans at the full-bloom stage, where regrowth stilI occurs, and obtained a grain yield of 80 per cent of the untreated beans, which averaged 37.2 bushels per acre. No data on extent of regrowth are indicated. Real understanding of dry matter accumulation will be made possible by studies on soybeans similar to those currently being made on corn at Cornell University ( Musgrave and Lemon, unpublished data). Here factors determining day-to-day and hour-to-hour growth are being identified and characterized. Preliminary results for corn promise significant reappraisals.

232

A. J. OHLROGGE

Ill. Nitrogen A. CONCENTRATIONS IN THE PLANT I. Prebloom Nitrogen concentrations are high in the seedling soybean. Six-day-old plants with the cotyledons removed for analysis contained from 8.2 to 9.8 per cent N (Murneek, 1937). The cotyledons contained up to 10.4 per cent N. In 20 days these values had declined to about 3 per cent in the stems and 5 per cent in the leaves. The short-day plants maintained significantly higher nitrogen concentrations than the long-day plants. Percentages almost as high (7.8 per cent) are reported by Webster (1928). Again, the leaves and stems had about the same nitrogen content. The concentrations had decreased to 2.7 and 1.1 per cent for the leaves and stems, respectively, by the onset of blooms. The absolute minimum concentration must approach the value of 1.5 per cent N reported by Hampton and Albrecht (1943) for 35 day-old, nonnodulated beans grown in the absence of nitrogen with the colloidalclay-sand technique of Missouri. Soybeans 25 days old, grown out of doors in nutrient culture by Lathwell and Evans (1951) contained 4.7 per cent N with 100 p.p.m. N in the nutrient solution or 2.6 per cent with 21) p.p.m. The lower concentration was fairly well maintained through flowering, when the substrate concentration was kept either at 20 p.p.m, or increased to 100 p.p.m. In contrast, the high (4.7 per cent) concentration declined to less than 3 per cent even when the 100-p.p.m. level was maintained or when it was decreased to 20 p.p.m.

2. Bloom Murneek (1937) studied in detail the nitrogen content of the flowering Biloxi soybean. No wide difference in total nitrogen between the internodes and nodes plus tips was found. The leaves of flowering plants contained about a third more nitrogen than the stems. There was, however, from the base of the plant to the top, “an ascending gradient in total, coagulable, proteose, basic ammonia, and humin forms of nitrogen” in both vegetative and reproductive soybean plants. “Excepting for the base, a descending gradient in the same direction exists for nitrate, amino and amid forms.” The lowest total nitrogen contents of leaves and stems were 2.5 and 1.5 per cent, respectively. Webster’s ( 1928) greenhouse-grown beans with leaves analyzing 5.2 per cent N represent a high value. The stems contained about 1 per cent N. In Ohio studies, the extremes for total nitrogen for flowering plants were from 1.5 to 3.1 per cent N (Lathwell and Evans, 1951).

MINERAL NUTRITION OF SOYBEANS

233

Other greenhouse studies in Iowa showed ranges from 1.2 to 3.5 per cent N. Included are inoculation and fertilization studies ( Allos and Bartholomew, 1959). Under standardized greenhouse growing conditions, Erdman and Means (1952) found correlation coefficients of 0.98, 0.89, and 0.98 for three soybean varieties when the total dry matter yield was correlated with the amount of nitrogen recovered in the plant. Thc linear relationship indicates constant nitrogen contents in these inoculant studies. Erdman’s (1929) field samples show little variation in total nitrogen. Likewise, the studies of Hammond et al. (1951) ranged only from 2.5 to 2.9 per cent total nitrogen for the tops during this period, Togari et al. (1955) divided the tops into leaves and stems. About four times more nitrogen was found in the leaves than the stems: 4.0 and 1.0 per cent.

3. Pod Filling The differences in nitrogen concentrations of the plant parts which develop in the flowering stage grow larger during pod filling. The contents of the seeds are fairly constant and change little during development, whereas the pods, stems, and leaves decline in nitrogen. As an example, the seeds in the Iowa studies contained 6.2 to 6.3 per cent N while the pods declined from 2.45 to 0.88 per cent on the Webster and 1.90 to 0.71 per cent on the Clarion soil. The composited leaves and stems declined from 2.42 to 0.44 per cent and 2.16 to 0.45 per cent for the Webster and Clarion soils, respectively (Hammond et al., 1951). The decrease in the pods of the Japanese-grown beans was from 4.0 to 1.0 per cent N (Togari et al., 1955). The high initial value may be the result of combining pod plus embryo seeds in the first samples; this is not clear in the article. The final leaf and stem concentrations were 3.5 and 1.0 per cent N, respectively.

B. RATEOF UPTAKE At emergence, 30 per cent of the protein had disappeared from the cotyledons. Nine days later, 75 per cent had been removed, and the final amount in the cotyledons was 7 per cent of the original ( McAlister and Krober, 1951). Yoshira and Kawanshee ( 1956) likewise found that most of the nitrogen had moved to the seedlings in the first 3 weeks after planting. The relative contribution of the soil and the cotyledons to the early nitrogen nutrition has not been studied. Murneek‘s ( 1937) photoperiod studies indicate that nitrogen uptake from the soil may begin very early. This of course does not indicate the necessity of an outside source. Also, McAlister and Krober (1951) showed that removal of cotyledons 4 days

234

A. J. OHLROGGE

after emergence had no effect on plant development. Takeshima (1952) obtained quite similar results. Nitrogen uptake per day (soil plus symbiotic) occurred at a constantly increasing rate reaching a peak of 4.4 pounds per acre per day 3 months after planting on the Webster soil (Hammond et al., 1951). The rate of change with time was practically constant. Uptake rapidly declined after reaching the peak. All other studies both in the field and in the greenhouse show the importance of nitrogen during the flowering and pod-filling period (Togari et al., 1955; Yoshihara and Kawanshee, 1956; Lathwell and Evans, 1951). No studies have been reported that are sufficiently refined to detect daily rate changes or changes associated with plant development. Although maximum rates occur in the podfilling stage, continued vegetative growth based on projection of rate curves would probably have similar high rates. Such projections of course exclude the initial and final growth periods. C. REDISTRIBUTION Most of the nitrogen moves from the cotyledons in the seedling phase. Likewise most of the nitrogen moves from the vegetative plant parts into the seed. This is vividly demonstrated in the field data from Iowa (Hammond et al., 1951) : "During the period from the 87th day to maturity at 136 days, the total nitrogen content of the plant increased 48 pounds per acre, but the nitrogen content of the seeds and pods increased 121 pounds and that of the remainder of the plant decreased 73 pounds." The redistribution of nitrogen is also indicated by its decline after the organs have reached maturity. With this criterion, Togari et al., (1955) report the percentage of the various nutrients translocated from each plant organ. Translocation of nitrogen does not appear to be able to meet the entire later demands of the crop, because sufficient nitrogen cannot be accumulated in the vegetative parts. Lathwell and Evans (1951) grew inoculated soybeans outside in nutrient culture and supplied 120 p.p.m. N to mid-bloom; however, these needed more than 20 p.p.m. N during the remainder of the growth period to maximize grain yields. Similar conclusions were reached by Hawkes (1957) with the same technique in a preliminary study, The conclusion is supported by the extensive Iowa studies on the adequacy of the symbiotic nitrogen supply.

D. FERTILIZATION The symbiotically fixed nitrogen helps to meet the daily nitrogen requirements. Initially the seedling is exclusively dependent on the soil and seed leaves. Symbiotic nitrogen supplies must await the invasion of

MINERAL NUTRITION OF SOYBEANS

235

the roots by rhizobia and development of nodules. Yoshihara and Kawanshee (1956) from sand and soil culture studies concluded that an outside source of combined nitrogen was needed only for the first 5 weeks. Thereafter, additional combined nitrogen did not increase forage yield. These results are at variance with the bulk of nitrogen fertilization studies. In the intensive investigations in Iowa, using N16 in the more recent work, increased yields were obtained by additional combined nitrogen. Allos and Bartholomew (1959), concluded that with the many species studied, “only about one-half to three-fourths of the total nitrogen” for maximum yields could be supplied by the fixation process. The importance of nitrogen in attaining maximum yield is emphasized by Lathwell and Evans ( 1951). Their yield of soybeans was closely correlated with the amount of nitrogen accumulated throughout the life cycle. Grain yield was determined by the number of pods retained by the plant, and this in turn was determined by the level of nitrogen available during the bloom period. This is also borne out by the high correlation coefficients reported for total nitrogen and dry weight by Erdman and Means (1952). The widely accepted inadequacy of the symbiotic mechanism for maximum yields suggests the possibility of fruitful research in nitrogen fertilization of soybeans. From the many studies conducted in this area, it has been clearly shown that as the combined nitrogen supply increases, the contribution of the symbiotic bacteria decreases. A remarkably fine linear correlation between the nitrogen fixation expressed as percentage of the total absorbed and the ratio of the nitrogen applied over the nitrogen absorbed, is reported for many species by Allos and Bartholomew (1959). This decrease in efficiency of the bacteria as the combined nitrogen is increased would suggest that relatively low rates of fertilizer nitrogen might be quite ineffective. This has generally proved true (Lyons and Earley, 1952). Very few fertilization rates high enough to compensate for both nutrient absorption and symbiotic inefficiencies have been tried. Those that have-Indiana ( Wilkinson, unpublished) , Ohio (Mederski et al., 1958), Illinois (Lyons and Earley, 1952)-have not resulted in spectacular grain yields. Usually an increase of 2 to 4 bushels is obtained for the lower nitrogen rates with decreases resulting from the high rates. No completely satisfactory physiological explanation for these results is found in the literature. They surely indicate that nitrogen is not a first limiting factor in soybean production; however, the decisive experiment has not yet been conducted.

236

A. J. OHLROGGE

IV. Phosphorus

A. CONCENTRATIONS IN THE PLANT I. Prebloorn The period of emergence to blooming represents many physiological changes in the plant. Therefore the mean figures lack precise meaning in relation to plant processes. Greenhouse studies employing nutrient solutions supply the best data on phosphorus concentration extremes in the tissue. The extensive studies in Ohio by Mederski (1950) on soybeans grown outdoors with a nutrient culture sand technique are revealing. The highest phosphorus level of 135 p.p.m. resulted in a depression of growth. One month after planting, the leaves, stems, and total tops contained 0.69, 0.58, and 0.65 per cent phosphorus, respectively. Ten days later and six days before the onset of blooms the upper leaves, lower leaves, stems, and total tops contained 0.74, 1.06, 0.76, and 1.05 per cent phosphorus, respectively. Thus, wide differences in content in plant parts occur and, as pointed out by Mederski, the lower leaves act as storage organs when excessive amounts of phosphorus are absorbed by the roots. Under these conditions the concentration of the upper leaves of 0.74 per cent must represent the upper limit for near normal growth. Highest contents found in the field are about one-half those in the nutrient solution studies. Wilkinson ( unpublished data, 1958) found 0.50 per cent phosphorus in the tops 42 days after planting. The beans were fertilized with a 40-160-0pounds per acre band application on a soil of medium phosphorus fertility. The most common concentrations for fertile soils are between 0.25 and 0.30 per cent (Hammond et al., 1951; Borst and Thatcher, 1931; Welch et al., 1949; Bureau et al., 1953; Togari et al., 1955). The minimal concentration in prebloom plants grown in nutrient solutions at 5 p.p.m. phosphorus (Mederski, 1950), was 0.30, 0.15, and 0.25 per cent for the leaves, stems and total tops, respectively. These values are in excess of phosphorus deficient field grown beans where concentrations of less than 0.20 per cent are often found (Bureau et al., 1953). The absolute minimum might easily be determined by analyzing plants the only source of phosphorus of which is their cotyledons. Such data have not been found. It is estimated that this value would be between 0.14 and 0.18 per cent phosphorus for the total tops. Thus, in the prebloom stage there is about an eightfold range in phosphorus concentration.

MINERAL NUTRITION OF SOYBEANS

237

Examination of numerous data suggests an optimum range for the total tops of between 0.25 and 0.45 per cent phosphorus for the prebloom stage. Higher concentrations would represent accumulations resulting from other factors limiting growth, and lower concentrations would represent inadequate phosphorus supplies or interference in phosphorus absorption. 2. Bloom The maximum concentrations of phosphorus are found in plants grown in nutrient solution. Here also, wide differences between plant parts are found. The highest concentration, 1.64 per cent, was found in the lower leaves of beans grown in solutions containing 125 p.p.m. phosphorus (Mederski, 1950). The upper leaves analyzed 0.74, the stems 0.67, and the total tops 1.14 per cent. Values in Japan are similar to values in the United States for field-grown beans: 0.31, 0.09, and 0.24 per cent for leaves, stems, and total tops, respectively (Togari et al., 1955). The Indiana 40-160-0 treatments previously mentioned produced tops analyzing 0.33 per cent phosphorus. Austin (1930) reports a Michigan analysis high of 0.43 per cent for 73-day-old field-grown plants. The minimum concentrations are indicated by solution experiments in which all the sources of phosphate were removed for various periods during growth. Seventeen days after removal of phosphorus from plants previously supplied with 5 p.p.m. phosphorus in the substrate, the concentrations in the plants in the Ohio experiment still exceeded the concentrations usually found in the field (Mederski, 1950). Soybean hay for animal nutrition studies in North Carolina probably come close to the physiological minimum. During the 1946 to 1948 period, pIants from the unphosphated field plots ranged from 0.06 to 0.08 per cent phosphorus in the stems and 0.16 to 0.18 per cent in the leaves (Matrone et al., 1954). Beeson et al. (1948) grew beans outdoors in 2-gallon crocks and reported a range in phosphorus concentration in the leaflets of blooming plants of 0.1 to 0.3 per cent phosphorus. The tops averaged 0.14 per cent. Thus the data indicated about a seven- to ninefold range in phosphorus content during the bloom-podding stage. The content most often reported at this stage for beans grown on fertile soil is about 0.25 per cent phosphorus. Consideration of all the reported values indicates that concentrations between 0.25 and 0.35 represent optimal nutrition, with values found above and below representing luxury consumption and deficiencies, respectively.

3. Pod Filling At the end of August the plants of the high phosphorus cultures of Mederski (1950) contained 0.90 per cent phosphorus in the lower leaves,

238

A. J. OHLFIOGGE

0.76 per cent phosphorus in the upper leaves, and 0.53 and 0.34 per cent phosphorus in the stems and pods, respectively. The total computed concentration in the tops was 0.54 per cent. Even higher values result when other nutrients limit growth. In a greenhouse experiment by Webb et aZ. (1954), where Mg was extremely limiting, the mature plant parts contained phosphorus as follows: leaflets 1.03 per cent, petioles 0.75 per cent, stems 0.96 per cent, roots 1.32 per cent, pods 1.00 per cent, seeds 0.84 per cent, and whole plant 0.98 per cent phosphorus. With phosphorus supplied early and then removed from the cultures, Mederski (1950) found that the phosphorus concentrations decreased to 0.07 per cent in the upper leaves; 0.06 per cent in the lower leaves; 0.03 per cent in the stems; 0.07 per cent in the pods; and 0.05 per cent in the tops. These probably represent the minima, because samples harvested 10 days later had not materially changed in composition. Concentrations in the field-grown plants exclusive of the seeds are reported to be as low as 0.14 per cent (Hammond et al., 1951) and 0.11 per cent (Matrone et al., 1954). These data would indicate critical concentrations for the top exclusive of the seeds as 0.05,0.25 to 0.35,0.60 per cent as minimum, optimal range, and maximal concentrations, respectively. B. RATEOF UPTAKE The cotyledons are the initial source of phosphorus for the embryo plant. At emergence, which was 10 days after field planting, about 40 per cent of the phosphorus had been translocated. At 15 and 38 days after planting 75 and 92 per cent, respectively, was transferred to the seedlings (McAlister and Krober, 1951), Von Ohlen ( 1931) reported that only about one-half of the phosphorus was transferred from the cotyledons; however his plants were grown in the dark, thus organic reserves may have been the limiting factor in phosphorus transfer. No studies are reported showing the influence of soil phosphorus level or band fertilization on phosphorus transfer from cotyledons. This might be a simple, rapid method for measuring plant-available soil phosphorus levels. The time at which first uptake of soil phosphorus occurs has not been determined. However, it would seem logical to assume that it occurs soon after the emergence of the root. Three to five days after emergence the seedling is largely dependent on soil phosphorus, as indicated by low transfer rates from the cotyledons. In greenhouse studies, however, the writer has observed that low levels of mineral nutrition were correlated with early yellowing, whereas high fertility levels delayed yellowing of the cotyledons. The change in rate of phosphorus uptake appears quite different for

MINERAL NUTRITION OF SOYBEANS

239

beans grown in nutrient culture from that found for beans grown in the field. Mederski’s (1950) data suggest an increasing rate of uptake for the first 40 to 50 days and then a fairly constant rate until leaf yellowing. This pattern was true for beans grown at both the 5-p.p.m. and 45-p.p.m. levels of phosphorus. Iowa (Hammond et al., 1951), Ohio (Bureau et al., 1953), Indiana ( Wilkinson, unpublished data, 1958), and North Carolina (Welch et al., 1949) data suggest a constantly increasing rate of uptake after the initial seedling lag, reaching a maximum of 0.40 pounds of phosphorus per acre per day during the filling of the pods at the high phosphate levels. With the low phosphate treatments, the rate curve is much more erratic, with no clear pattern distinguishable. The field data from Japan (Togari et al., 1955) more closely approximate the Ohio nutrient culture results. From the setting of pods, the total phosphate uptake remained constant until maturity. The phosphorus concentration of the vegetation indicated that the beans were grown at a medium level of phosphorus availability. Hammond et al. (1951) pointed out that the ever-increasing rate of phosphorus uptake was a result of the higher demand of the seeds. At maturity 82 to 85 per cent of the phosphorus in the plant was in the seed. All these rate curves represent a great deal of averaging, for the smallest time interval was usually 7 days. As is true for dry matter production, there must likewise be wide daily fluctuation in phosphorus uptake dependent on environmental conditions, plant status, and phosphorus availability. C. TRANSLOCATION The mobility of phosphorus in the plant was recognized early. Borst and Thatcher (1931) showed the decline in phosphorus concentration in leaves, stems, and pods of beans after the parts reached full development; however, only for the pod phosphorus did they point out its movement into the seed. The same movement for the leaf and stem phosphorus may have been inferred. Twenty years later, Mederski (1950), Hammond et al. (1951), and Togari et al. (1955) pointed out that from 40 to 80 per cent of the phosphorus in the seed may have been translocated from the pods, leaves, and stems, assuming that all the phosphorus disappearing from these organs moved into the seed. Hammond et al. (1951) showed that the largest relative transfers of phosphorus occur at low soil phosphorus levels. The phenomenon of phosphorus mobility has been convincingly confirmed by tracer methods (Biddulph and Woodbridge, 1952). Mederski (1950) showed that the removal of phosphorus from the nutrient solution at full bloom did not reduce the yield of beans. Excess, or luxury, consumption of phosphorus prior to bloom, and translocation

240

A. J. OHLROGGE

of the accumulated phosphorus were sufficient to sustain optimum yields. In greenhouse studies, Webb ‘et al. (1954) related the transfer of phosphorus to the seeds to the magnesium nutrition of the plant.

D. FERTILIZATION The advent of P32 made possible the precise determination of the contribution of fertilizers to the day-by-day requirements of the plant. Yet after ten years the understanding of the fertilizer’s contribution is still meager. Failure to increase grain yields consistently through phosphorus fertilization has probably discouraged detailed studies, when it should have had the very opposite effect. Early in the use of tracers it was demonstrated by Krantz et al. ( 1949) and Welch et al. (1949) that in the early stages of growth from 70 to almost 100 per cent of the plant phosphorus may be derived from the fertilizer. Both band and broadcast applications could supply this when appropriate rates of application, soil phosphorus levels, and placements were used. Although fertilizers were utilized, they replaced much soil phosphorus, resulting in only slight over-all increases in phosphorus uptake and yield. Although this was not stressed by Welch et al. (1949) or Krantz et al. ( 1949), their data showed clearly the availability of band-applied phosphorus toward the end of the growing season. The bulk of the fertilizer phosphorus was taken up 2 to 3 months after application. This is in direct contrast to corn, which absorbs its fertilizer phosphorus early in the growing season. Even more striking are the 1950 data from Ohio (Bureau et aZ., 1953). Here fertilizer uptake rates reached a maximum of 0.2 pounds per acre per day for the period 75 to 114 days after planting. On the low phosphorus level, soil with band-applied superphosphate at a 0-50-0 rate, 75 per cent of the phosphorus absorbed during this period was fertilizer derived. The resulting recovery of 47 per cent of the band-applied phosphorus is remarkable. Also, 83 per cent of the recovered phosphate was absorbed in the 39 days between “late full bloom” and “just before leaf fall.” The experiment was on a Wooster silt loam and was superimposed on several plots of a longtime experiment. The pattern of uptake was consistent for all four phosphorus sources and three levels of soil phosphorus in this factorial experiment. With the less available fused tricalcium phosphate, the recoveries were at a minimum of 10 per cent, which is still very high. The combination of highly available fertilizers on soils with low phosphate levels resulted in highly significant increases in total phosphate uptake in the pre-pod-filling stages, but by the last sampling, although the same trends existed, they were not statistically significant. Under these conditions of high phosphate uptake, the phos-

MINERAL NUTRITION OF SOYBEANS

241

phorus application resulted in small but consistent decreases in grain yield at a yield level of about 30 bushels per acre; this is a striking example of the paradox encountered in studies of soybean mineral nutrition. Many factors have been considered in an attempt to explain the high recovery of fertilizer phosphorus, of which two seem worthy of discussion. The periodic samples were obtained by overplanting and then thinning. The uptake per acre figures are the product of the per plant content of phosphorus and the number of plants per acre. A constant population value was used which would upgrade the final harvest value and downgrade the early values. A more significant factor may be the result of root proliferation in the fertilizer band resulting from the decay of the root systems of the previously harvested plants. Duncan and Ohlrogge (1958) and Ohlrogge (1958) have stressed the stimulatory effect on root growth of nitrogen and phosphorus in the fertilizer band. The decaying roots not only would supply a small amount of released phosphorus, but the nipogen and organic matter might cause a spate of new root growth, providing an abundance of absorption surfaces. The result would be a flush of uptake of fertilizer phosphorus during the peak demand period. Data of 1957 and 1958 from Indiana (Wilkinson, unpublished data, 1958), also based on thinning samples but with the results expressed on a per plant basis, showed a consistent decline in the percentage of fertilizer-derived phosphorus taken up during each period. Initially 50 to 80 per cent of the plant phosphorus per period was fertilizer derived. The final period showed that 5 to 12 per cent was fertilizer derived. The recoveries based on the product of the final stand and fertilizer phosphorus per plant ranged from 9 to 21 per cent. Again there were no significant grain yield increases although significant early response in dry weight and total phosphorus content of plants was obtained. What do these data on phosphorus indicate? Certainly a large part of the plant phosphorus can be derived from the fertilizer. Also the total uptake of phosphorus may be and frequently is increased somewhat. There is, however, no assurance of an increase in yield. Thus, phosphorus does not appear to provide the exclusive key to unlocking the soybean fertilization mystery. V. Potassium A. CONCENTRATIONS IN THE PLANT 1. Preblom The extremes in potassium concentration reported in the literature are 0.30 to 5.7 per cent. The lower value was obtained by Allen (1943)

242

A. J. OHLROCGE

for beans grown in a potassium-deficient nutrient solution and the higher value was reported by Hutchings (1936) in a study of the effect of phosphate level on the nodulation and growth of soybeans. The Missouri dialyzed clay-sand mixture was the growth medium. Many other values between these limits are reported. The lowest concentration for field grown beans was reported from Michigan-0.5 per cent K for 35-day-old beans (Austin, 1930). Japanese analyses of bean stems and leaves showed 4.2 per cent K and 2.6 per cent K, respectively (Togari et al., 1955). Borst and Thatcher (1931) found 3.6 per cent in the stems and 2.3 per cent in the leaves of MANCHU soybeans, The PEKIN variety analyzed 1.5 and 1.4 per cent K in the stems and leaves in the late prebloom stage. Iowa studies report 1.2 to 1.6 per cent K for total tops in the prebloom stage (Hammond et al., 1951). They indicate that no known shortages of mineral nutrients existed, although the basis for the statement is not known. Allen (1943) found dry matter yields leveled off at potassium concentrations in the tops of vmGmu and MORSE varieties at 2.7 and 3.5 per cent, using nutrient solutions of 78 and 312 p.p.m. K. The data for the prebloom stage would suggest a minimum value of 0.3 per cent, an optimal range of 1.0 to 4.0 per cent, and an upper limit of 5.7 per cent K. No data were found on the potassium concentration associated with the appearance of deficiency symptoms. 2. Bloom

Total potassium concentrations for field-grown beans show the following ranges: Iowa (Hammond et d.,1951), 0.8 to 1.0 per cent; Ohio (Borst and Thatcher, 1931), 0.9 to 1.2 per cent; Michigan (Austin, 1930), 0.5 to 0.8 per cent; Indiana (Wilkinson, unpublished, 1959), 1.2 to 4.5 per cent; Japan (Togari et al., 1955, and personal communication), 2.2 to 3.6 per cent. A wider range in contents is found in the plant parts. Evans et al. (1950), using spectrographic analysis, report a minimum of 0.18 per cent K in the lower leaves of plants grown in solutions with toxic levels of magnesium. The highest concentration was 1.75 per cent for upper leaves of plants grown in manganese-free nutrient solution. The solution cation concentrations were: potassium, 90 p.p.m., calcium, 180 p.p.m., and magnesium, 55 p.p.m. The potassium concentration in the leaves of plants grown in complete solutions increased from 0.60 per cent for the lower leaves to 0.84 per cent for the upper leaves. These values are about the same as the six-year average of 0.4 per cent for roots, 1.6 per cent for pods, 0.9 per cent for the total tops very late in this period, obtained by Borst and Thatcher (1931) for field-grown soybeans. The

MINERAL NUTRITION OF SOYBEANS

243

stems and leaves of these plants analyzed 1.5 and 0.8 per cent K, respectively. The Japanese experiments showed the stems decreasing from 3.2 to 1.8 pr cent K, whereas the leaves remained close to 2.2 per cent during this period. Based on the dry weight of the plant parts, the total plant would analyze about 2.0 per cent K. These data suggest that at high levels of potassium the stems, lower leaves, and upper leaves accumulate potassium in that order. Minimal and maximal concentrations and optimal range, in the tops of 0.3, 4.5, and 0.7 to 2.0 per cent K, respectively, are suggested by these data.

3. Pod Filling Only data on field-grown samples collected before leaf fall are reported for this stage of development. Six-year average figures from Wooster, Ohio, show leaves declining from 1.0 to 0.4 per cent K during this stage. Similar declines were found in the stems, 0.8 to 0.3 per cent; and the pods, 1.6 to 0.9 per cent; whereas the seeds remained close to 1.6 per cent K. Results from plots at Columbus, Ohio, showed the same trends (Borst and Thatcher, 1931 ), The decreases in potassium concentrations are not as great in the Iowa data (Hammond et al., 1951). The leaf plus stems samples on both soils declined from 0.7 to 0.5 per cent K. In contrast, the Japanese soybean stems and leaves declined from 2.3 to 0.6 per cent and from 2.3 to 1.6 per cent, respectively (Togari et al., 1955). The seeds had an initial concentration of 2.9 per cent K and declined to 1.6 per cent K at maturity. Indiana survey leaf samples from the third, fourth, and fifth nodes of plants from sixty-seven fields varying widely in maturity from pod set to near maturity ranged in potassium concentrations from 0.2 to 4.0 per cent K. The content of potassium associated with the onset of foliar deficiency symptoms is reported only by Nelson et al. (1945). In a potassium and magnesium experiment, five levels of potassium were applied. Extreme deficiency symptoms occurred early in the untreated plants. At the highest potassium rates, no symptoms were observed. Leaflet and petiole samples were collected from the third and fourth nodes from the top at the early pod-filling stage; analyses showed 0.48 and 0.7 per cent, respectively, for the no-potassium plots; and 2.1 and 1.6 per cent, respectively, for the plots receiving 120 pounds K 2 0 per acre. It is unfortunate that similar data have not been collected on the many other fertilizer experiments reported in the literature. Because of these extremes in the potassium concentrations of the various plant parts, an average figure for the total plant during the 4- to 6-week period would have little meaning. It is clear that the stems may

244

A. J. OHLROGGE

range from less than 0.3 per cent K to more than 3.0 per cent K for a mature plant. The leaves may range from 0.4 per cent to 3.0 per cent and the pods from 0.8 to 3.0 per cent. B. RATEOF UPTAKE The peak rate of potassium uptake--1.7 pounds per acre per dayoccurred in the 87- to 94-day interval which coincided with the nitrogen peak in the Iowa data on the Webster soil (Hammond et aZ., 1951). Potassium showed more week-to-week variations in uptake rate than calcium, magnesium, nitrogen, or phosphorus. The data of Togari et al. (1955) expressed on a per plant basis and as interpreted from the accumulation curves showed a much more constant trend. Since the Iowa plants were much lower in potassium, the greater variation in weekly uptake may be the resuIt of the lower level of available potassium in the soil. Hammond et al. (1951) point out, however, that potassium was not a known limiting factor in growth. Six-year averages reported by Borst and Thatcher (1931) show a constantly decreasing rate of potassium uptake during the pod-filling period. The average dry matter production of 4500 pounds per acre indicates only average yields. What is the shape of the ideal rate curve? It cannot be determined from present potassium uptake data. The irregularity in the Iowa data and insufficient samples taken in the Japanese work preclude any sound conclusion. The precise need curve could only be determined by finding the critical periods and levels in potassium withdrawal studies.

C. TRANSLOCATION Potassium is readily translocated in the plant. Fifteen days after planting, 50 per cent of the potassium had been moved out of the cotyledons of field-grown beans ( McAlister and Krober, 1951). After 38 days only 20 per cent of the original potassium was in the cotyledons. All the potassium was translocated within 25 days when the beans were grown in the dark and in a nutrient-free medium (Von Ohlen, 1931). The extent of translocation is probably dependent on the potassium available to the roots of the seedlings. The occurrence of potassium deficiency symptoms on the lower leaves indicates redistribution during the bloom and podding stage. Foliar potash deficiency symptoms have been reported to occur first on the younger leaves (Nelson et al., 1945), suggesting immobility; however, a more likely explanation is that the rate of translocation to the newly developed leaves may not have been sufficiently rapid to meet the requirements of the new leaves. The extensive literature on trans-

MINERAL NUTRITION OF SOYBEANS

245

location to the seed re-emphasizes the mobility of potassium. The possibilities of s d c i e n t accumulation in early stages to carry the plant through periods of complete withdrawal has not been explored. However, the calculated translocatable potassium based on a 4 to 5 per cent content in the vegetative portion is enough to meet the total potassium requirement of the seed of an average crop,

D. FERTILIZATION Some of the most striking responses to fertilization of soybeans have been with potassium salts. Consistently large grain yield increases have been measured on almost all the potash-deficient soils of the Southeast when good production methods are used (Nelson, 1946). In the Midwest, responses have not been as consistent. Most are obtained on the sandier soils and high organic matter prairie soils. Soybeans grown on the poorly drained, light-colored silt loams have not responded consistently to potassium application even when potash deficiency symptoms are prevalent ( Ohlrogge, unpublished). Although increases in potassium concentration within the plant to both broadcast and band applications are obtained, they do not always increase yields. These and other data would indicate that fertilizer potassium utilization is not in itself a problem. VI. Calcium A. CONCENTRATIONS IN THE PLANT

1. Prebloom A tenfold range (0.26 to 2.8 per cent) is found in the calcium concentration of the total soybean plant in the prebloom stage. The distribution of calcium concentration between the extremes is not so uniform as for the phosphorus and potassium. Numerous calcium values are reported by Missouri workers using the clay-sand growth medium (Hampton and Albrecht, 1944; Graham and Turley, 1947; Harston and Albrecht, 1942; Brown and Albrecht, 1947; Allen, 1943). These were usually at fairly low calcium levels, and the concentrations fell between 0.26 and 0.76 per cent. Moser (1943) in a nutrient culture factorial study with three pH levels and four calcium levels reported calcium contents of 0.26 to 0.90 per cent in 30-day-old plants. Numerous Michigan studies report calcium concentration ranges as follows: 2.1 to 2.8 per cent for many samples of 35-day-old field and greenhouse soybeans (Austin, 1930); 0.85 to 1.93 per cent for soil-grown beans in a boron study (Muhr, 1940); 0.29 to 0.74 per cent for soybeans grown in sterile nutrient culture; and 0.71 to 1.20 per cent for beans grown in a fumigated soil (Siege1 et al., 1952).

246

A. J. OHLROGGE

Few studies report the calcium content of field-grown beans in the prebloom stage. Likewise, there is little discussion of foliar symptoms, nutritional levels, or critical concentrations. The apparent abundance of calcium under field conditions may have removed the incentive for studies of calcium nutrition. Hashimoto and Okamoto (1954) have fractionated the calcium in the plant parts in a magnesium study into water-soluble, acetic acidsoluble, hydrochloric acid-soluble, and insoluble calcium. The soil was very acid and only lightly limed, yet high concentrations of calcium were found. The leaves varied from 2.3 to 2.6 per cent and the stems 1.6 to 1.9 per cent calcium. Togari (personal communication, 1959) recorded 1.6 to 2.1 per cent calcium in field-grown plants. Periodic samplings between the 22nd and 55th days after planting show a constant decline in percentage of calcium from 1.9 to 1.4 on both the Clarion and Webster soils (Hammond et al., 1951). 2. Bloom Spectrographic analyses of intermediate leaves from nutrient culturegrown beans showed a range from near zero to 6.5 per cent. The low value is for plants from the solution lacking calcium and the higher value is for the potassium-free solution plants. A wide range in the calcium concentration was found between the upper and lower leaves of the manganese-deficient plants. The lower leaves analyzed 5.1 per cent, whereas the upper leaves analyzed 1.0 per cent calcium (Evans et al., 1950). Soybeans harvested from solution cultures with wide ranges of calcium, potassium, and magnesium in the solution, had a much smaller range in total calcium: 1 to 300 p.p.m. in substrate-produced plants, with 0.5 to 1.5 per cent calcium in the leaf and 0.3 to 1.4 per cent in the stem (Hashimoto, 195513). Total calcium in soil-grown plants, considered as a group, was lower than the nutrient culture soybeans. Soybeans sampled in each of three years in an animal nutrition study in North Carolina (Matrone et al., 1954) ranged in calcium concentration from 0.69 to 0.88 per cent. These plants were in the late bloom or early pod-fillhg stage. Numerous samples from a fertilizer experiment in Indiana ( Wilkinson, unpublished, 1958) ranged from 0.49 to 1.04 per cent, and Austin’s (1930) 73-day-old plants ranged from 1.7 to 2.0 per cent. Unusually low values of 0.10 to 0.13 per cent for soil-grown beans are reported by Vanderford (1940). The range for the leaf and stem in Hashimoto and Okamoto’s (1954) magnesium experiment was 2.2 to 3.3 per cent for leaves and 1.5 to 1.9 per cent in the stems.

MINERAL NUTRITION OF SOYBEANS

247

Consideration of all the above values indicates a fifteenfold range (0.4 to 6.5 per cent). A suggested optimal range is 1.0 to 3.0 per cent.

3. Pod Filling Nutritional survey samples collected by Wilkinson (unpublished, 1958) from farmers’ fields ranged in calcium content from 0.9 to 4.4 per cent. The samples were made up of the petiole and leaflets from the third, fourth and fifth nodes and represent maturity stages from early pod setting to near mature plants. Seventh and eighth nodal leaflets and petioles from fertilizer experiments analyzed 0.7 to 1.4 per cent calcium. Total plant samples (110 days after planting) ranged from 1.2 to 2.1 per cent calcium (Austin, 1930), which approximates the 0.90 to 1.53 per cent range reported by Morrison (1956) for soybean hay of various qualities. Japanese values for leaves range from 2.0 to 2.4 per cent; stems 0.7 to 1.6 per cent (Hashimoto, 1953), and total plant 1.1 to 1.4 per cent ( Togari, personal communication, 1959). Here, again, as is true for many other nutrients, the widest range in calcium content is found in the younger plants. It is surprising that critical values have not been discussed in the literature. The data reported give indications of the maximal, minimal, and optimal ranges; however, caution must be used in emphasizing unconfirmed unusually low or high values. B. RATE OF UPTAKE, REDISTRIBUTION, AND FERTILIZATION The initial transfer of calcium from the cotyledons is small. McAlister and Krober (1951) found no movement from, but rather transfer into, the cotyledons beginning shortly after emergence. Forty days after emergence the cotyledons had increased 300 per cent in total calcium. The only discussion of calcium uptake rates found is that by Hammond et al. (1951). The rate gradually increased, reaching a peak of 2.7 pounds per acre per day for the 73- to 80-day interval on the Webster soil. Gross uptake rates might be calculated from the Japanese study or approximated from dry matter accumulation data and composition values; however, such estimation would add little to understanding the day-to-day calcium nutritional requirements of soybeans. The immobility of calcium in the plant is well recognized. This immobility lends increasing importance to gaining a complete understanding of the day-to-day requirements of the plant. The abundance and relatively low cost of calcium has apparently discouraged research in calcium nutrition, but this does not preclude the possibility of a vital role for it as a factor limiting yields of soybeans. Soybeans at low yield levels are unusually tolerant of soil acidity but

248

A. J. OHLROGGE

do respond markedly to lime applications. A constant supply of calcium is required by the plant because of the immobility within the soybean. There are many other positive effects of liming, in addition to making calcium available to the plant. Since liming is a wide-spread practice in the acid soil areas of the soybean belt, little work has been done to evaluate calcium as a nutrient in field soils.

VII.

Magnesium

A. CONCENTRATIONS IN THE PLANT 1. Prebloom A fifteenfold range in magnesium concentration has been found in the prebloom stage-0.092 to 1.49 per cent. The lower value was found in 38-day-old beans grown in a magnesium-free nutrient culture (Webb et al., 1954) and the higher value from a study of the influence of potassium levels in nutrient culture (Allen, 1943). Other values from nutrient solution and soil studies in the greenhouse are fairly uniformly distributed within these limits. Studies by Austin (1930) gave values from 0.27 to 0.66 per cent magnesium in the total tops. Prebloom samples for two soils were practically constant at 0.8 per cent magnesium in an Iowa study (Hammond et al., 1951). On an acid, magnesium-deficient Japanese soil the application of 500 pounds per acre of MgS04 7Hz0 increased the magnesium content equally in the leaves, stems, and whole plant from 0.1 to 0.5 per cent total magnesium ( Hashimoto, 1953). Small differences in the magnesium concentration between the plant parts were found by Webb et al. (1954) for both deficient and normal plants. The roots 0.89 per cent and the petioles 0.50 per cent were the extremes for the normal plant. Deficient plants ranged from 0.089 per cent for the tops to 0.12 per cent for the roots. The magnesium-starved plants began to show defi'ciency symptoms 10 days after emergence, These values are in good agreement with those of Hashimoto (1953), who suggests that the onset of foliar symptoms is associated with a total magnesium content of 0.1 per cent in field-grown soybeans.

-

2. Bloom Austin (1930) reported 73-day-old plants which analyzed 1.0 per cent; these are the highest reported in the literature for total plant tops. This is twice the value found in the lower leaves of beans grown in nutrient culture with toxic levels of magnesium (Evans et al., 1950). The magnesium-free culture produced plants with near zero magnesium (spectrographic analysis). The normal and magnesium-free cultures of

MINERAL NUTRITION OF SOYBEANS

249

Webb et al. (1954) grew plants containing 0.50 per cent Mg and 0.85 per cent Mg,respectively. Extremely deficient plants showed very little difference in magnesium concentration in the plant parts: 0.060 per cent in the petioles, 0.063 per cent in the stems, and 0.091 per cent in the leaflets. The difference in the normal plants was of proportional magnitude: 0.46 to 0.63 per cent. Greater differences might have been found by separating the leaves into upper and lower leaves. In the Iowa study, tops, excluding young pods, contained about 0.8 per cent Mg. The pods contained 0.6 per cent Mg (Hammond et al., 1951). Webb et al. (1954) suggest that the onset of deficiency symptoms in the leaves of flowering plants is associated with a magnesium concentration of 0.24 per cent in a composite leaf sample. The concentration in the deficient leaves only would be somewhat lower. The leaves of the normal plant contained 0.367 per cent Mg. Eleven of fifteen soils responded to magnesium application in a greenhouse test in Missouri (Graham et al., 1956). The range in magnesium concentration for the total tops was from 0.19 to 0.48 per cent, the larger yield increases being obtained when the concentration of the magnesiumfree cultures was less than 0.25 per cent. Over forty total plant samples in fertilization experiments in Indiana ( Wilkinson, unpublished, 1958) ranged from 0.36 to 0.74 per cent Mg. 3. Pod Filling

Austin’s (1930) 110-day field-grown beans ranged from 0.53 to 0.79 per cent Mg. Petioles and leaflets from the third, fourth, and fifth nodes from an Indiana survey of 67 samples from farmer’s fields ranged from 0.21 to 1.00 per cent Mg. Petiole and leaflet samples from the seventh to ninth nodes in a fertilizer experiment in Indiana ranged from 0.33 to 0.55 per cent. Both groups were analyzed spectrographically ( Wilkinson, unpublished, 1958). During the pod-filling period, the Iowa tops without pods remained at 0.8 per cent Mg until the last 20-day period when they dropped to 0.4 and 0.6 per cent, respectively on the Webster and Clarion soils. Much lower concentrations are reported by Nelson et al. (1945) for leaflets and petioles from the third and fourth nodes from the top in an experiment in which magnesium increased yields. Without magnesium the leaflets and petioles contained 0.13 and 0.18 per cent Mg, respectively. With 36 pounds of magnesium applied as the sulfate, these parts contained 0.18 and 0.24 per cent Mg, respectively. Typical deficiency symptoms were common in the untreated magnesium plots. These values are in good agreement with the extensive Japanese study (Hashimoto, 1953). The stems and leaves had equal concentrations of total magne-

250

A. J. OHLROCGE

sium; the minimum was 0.05 and the maximum was 0.35 per cent. Although the combined stem and leaf samples had equal contents of magnesium, there was a wide difference between the upper and lower leaves in both the treated and untreated plots. The untreated plants on July 2 had 0.05, 0.10, and 0.22 per cent Mg in the lower, middle, and upper leaves. Chlorosis was recorded for the lower leaves. The magnesiumtreated plot had 0.25, 0.32, and 0.36 per cent Mg in the lower, middle, and upper leaves. By August 2 the difference between the lower and upper leaves had almost disappeared at all magnesium levels. A nutrient solution cation level study, also by Hashimoto (1955a), showed equal contents in the stems and leaves and equal ranges of 0.2 to 0.6 per cent Mg. The distribution and range in magnesium concentration that can be found in near-mature plants is best indicated by the greenhouse nutrient culture experiments of Webb et al. (1954). Magnesium was withdrawn from the solution for various periods of time. The plant parts were analyzed separately. The magnesium percentages were as follows: leaflets, 0.05 to 0.68; petioles, 0.03 to 0.56; stems, 0.20 to 0.45; roots, 0.06 to 0.53; pods, 0.05 to 0.88; seed, 0.14 to 0.36; whole plant, 0.06 to 0.53. The greatest ranges are found in the pods, roots, and leaflet and petioles. These are equal to those found in the prebloom stage.

B. RATE

OF

UPTAKE,REDISTRIBUTION, AND FERTILIZATION

The initial magnesium requirements are met from the cotyledons. From germination to emergence only one-fourth of the magnesium moved out of the cotyledons. From the 28- to 37-day period after emergence the cotyledons gained in magnesium ( McAlister and Krober, 1951). Nutrient culture beans grown by Webb et al. (1954), reached a peak uptake rate of almost 5 mg. of magnesium per plant per day for a 5-day period of full bloom with lower pods developing. The rate curve approximated the dry matter curve without having nearly as pronounced a peak, The field rate data from Iowa show a gradual increase reaching a maximum in the 73- to 80-day period of 1.4 pounds of magnesium uptake per acre per day, which closely parallels the calcium curve (Hammond et al., 1951). The lower concentration of magnesium in the seeds as compared to the vegetative plant parts accounts for the rapid decline in uptake rate during pod filling. This does not occur for phosphorus and potassium, the concentrations of which are high in the seed relative to the remainder of the plant. The data on magnesium outgo from cotyledons indicate a moderately low level of mobility in the seedling plant ( McAlister and Krober, 1951).

MINERAL NUTRITION OF SOYBEANS

251

Only one-fourth of the magnesium was translocated from the seed leaves in contrast to the almost complete removal of potassium and phosphorus, and no transfer of calcium. This may be contrasted with the results from the magnesium-withdrawal nutrient-culture study of Webb et al. (1954). The 21-day-old plants weighed 1.0 g. and analyzed 0.69 per cent Mg. At this time all magnesium was withheld from the nutrient solution, At maturity the plants weighed 18.4 g. and contained 0.062 per cent Mg. Almost half the magnesium in the mature plant was in the seeds and pods and represented translocated magnesium. Also, the magnesium concentrations in the vegetative portions were about 5 to 10 per cent of those in plants grown on 50 p.p.m. Mg for the entire growth period. The occurrence of foliar deficiency symptoms on the lower leaves and the differences in contents between the upper and lower leaves indicates high mobility for magnesium. Likewise, the decline in magnesium content with age for almost all magnesium levels in the Japanese work adds further support to magnesium mobility (Hashimoto, 1953). Soybeans grown on a magnesium- and potassium-deficient area of Coxville fine sandy loam in North Carolina responded significantly to applications of soluble magnesium (Nelson et al., 1945). The exchange complex of the soil was 4.5 per cent Mg saturated (0.15me./100 g.), and rates up to 36 pounds Mg were applied, resulting in a highly significant 6.8-bushel increase in grain yield. The magnesium effect on number of pods produced and retained was not consistent. Magnesium had no statistically significant effect on the size or distribution of pods or the degree of filling. The magnesium application of Hashimoto (1953) doubled the soybean dry weight per plant. Soybeans from eleven of fifteen soils responded to magnesium under intensive greenhouse cropping in Missouri (Graham et al., 1956). Fifty plants were grown to the full-bloom stage on 7000 g. of soil. The response correlated best with the magnesium extracted from the soil by 0.05 N HCl. The authors conclude, however, “In general, the soils with less than 10 per cent magnesium saturation of the total exchange capacity of the soil showed yield responses when magnesium was added.” These positive results would indicate there is no problem in obtaining magnesium responses on deficient soils. The most efficient and effective methods of applying magnesium would vary with the geographic region. VIII. Sulfur

Soybean plants characteristically exhibit only a small range in sulfur content. Eaton’s ( 1935) 2-month-old plants grown in nutrient culture with and without sulfur ranged only from 0.34 to 0.40 per cent and 0.12

252

A. J. OHLROGGE

to 0.27 per cent for the leaves and stems, respectively. Deficiency symptoms were described for the sulfur-deficient plants. Both the field and the greenhouse-grown bean samples (Austin, 1930) at various stages of growth varied from 0.22 to 0.32 per cent S . A somewhat wider range, from 0.12 to 0.52 per cent, is reported in the compilations of Beeson (1941) and Spector (1956). Sulfur uptake rate curves should parallel dry matter rate curves since composition appears fairly constant. A peak rate per day of about 1.5 pounds of sulfur per acre during the early and late podding stage might be predicted. Appearance of deficiency symptoms in the young leaves would indicate little mobility of sulfur ( Eaton, 1935). The small range of sulfur contents likewise gives evidence of little sulfur translocation in the plant. No sulfur translocation studies are reported. For almost fifty years sulfur fertilization has been practiced in the United States. The first area so treated was on the basaltic soils of the Northwest. Additional small sulfur-deficient areas in the North Central States have been identified. The relatively low sulfur requirement of crops in relation to the rain-out sulfur and that contained in fertilizers has discouraged much work with this element. The sulfur content of fertilizers is falling rapidly and the possibility of less rain-out and ever increasing plant demands as yields go up and more of the total plant is used, suggests that renewed attention to sulfur may be justified. Certainly there is a dearth of basic information on the sulfur nutrition of soybeans. IX. Iron A. INTRODUCTION There are only a few plant species in which the dependence of nutrient uptake and utilization have been studied in relation to the diverse genotypes within the species, The absorption and translocation of iron in soybean plants has been investigated to some extent from this point of view. Weiss (1943) first observed in 1938 the differential response of soybean strains growing on a calcareous soil, His genetic studies showed that efficiency in iron utilization is determined by a single recessive gene. The leaf and stem expressed sap of plants conditioned by this gene had relatively higher pH and lower soluble iron content. Also the total iron was higher and potassium lower in the total dry matter of these nutrient culture-grown plants. The controlling factor in iron utilization was further localized in the genotype of the root stock (Brown et al., 1958). Grafts of inefficient P.I. 54619-5-1 tops to efficient HAWKEYE rootstocks and vice versa demonstrated the significance of the rootstock in controlling iron uptake and mobility in the plant.

MINERAL NUTRITION OF SOYBEANS

253

In a further study using a split root system technique with part of the roots in calcareous soil and the remainder in a nutrient culture of controlled composition, Brown et al. (1959) found that the inactivation of iron in the P.I. 54619-5-1 roots is principally due to the combined effects of calcium and phosphorus. Precipitation of iron in the plant by phosphorus has long been recognized (Olson, 1938; Biddulph and Woodbridge, 1952) as an iron inactivation mechanism. The significance of plant acidity in keeping iron active has been stressed by correlating chlorosis with pH of expressed cell sap and organic acid levels (Weiss, 1943; McGeorge, 1949). More recently the role of the organic acids and other natural plant chelates in metal translocation has been emphasized (Zimmerman, 1956; Brown et al., 1959). The interplay of the metals in plant nutrition is exemplified by studies on the significance of the Fe:Mn ratio. Somers and Shive (1942) concluded that manganese toxicity and iron deficiency are the same. Normal plants are obtained only when the Fe:Mn ratio in the cuture solution is between 1.5 and 2.5. The ratios of soluble iron and manganese in the plant closely follow those of the solution. Much wider ratios were shown to produce normal plants by Ouellette (1951) if the manganese concentration was kept between 0.1 to 2.5 p.p.m. He also pointed out that manganese toxicity and iron deficiency symptoms are different. Warington (1954) also showed that manganese, vanadium, and molybdenum toxicity symptoms could be alleviated by increasing the iron supply in the nutrient culture. The Fe:Mn ratio has been suggested as controlling the redox potential of the plant (Hopkins et al., 1944). The functions of these metals in the metabolic pathways is becoming more completely understood. This will enable a clearer separation of the metal nutritional problems into uptake, translocation, and utilization phases which will help bring understanding to the gross nutritional relationships reported in the literature. B. CONCENTRATIONS IN THE PLANT Iron chlorotic leaves may contain more total iron than green leaves. For this reason several investigators have fractionated the iron in search of a component, the absence of which is well correlated with the development of chlorosis. Iron extracted with 1 N HC1 from dried leaves was highly correlated with chlorosis intensity in the leaves of several tree fruits (Oserkowsky, 1933). McGeorge (1949) used this method in a survey of field crops, including soybeans, and found a good relationship. He expressed the “active” iron as the percentage of the total iron. The iron concentration in the expressed sap of tissue was well correlated with iron deficiency by Weiss (1943). However, Somers and Shive

254

A.

J. OHLROGGE

(1942) used the same method of extraction but emphasized the Mn:Fe ratio as the most indicative of the levels of iron nutrition. Recognizing the limitations of total iron analyses the contents reported for plant parts still are of interest. The inactivation of iron in the roots is reflected in concentrations ranging from 50 (Brown et al., 1959) to 36,250 p.p.m. (Somers and Shive, 1942) for nutrient culture-grown beans, whereas the tops ranged in concentration from 32 (Brown et al., 1959) to 1100 p.p.m. (Weiss, 1943) for both greenhouse- and fieldgrown beans. Some field-grown hay samples are reported to contain in excess of 20,000 p.p.m. of iron; however, these probably represent contamination with soil. Several unusually low values of approximately 3 p.p.m. Fe in chlorotic leaves are reported by Wallace and Ashcroft (1956). Stems analyzed by these workers show concentrations about 40 per cent of that found in the leaves whereas Weiss’s (1943) values for stems are 20 per cent of that found in the leaves. Most of the numerous iron analyses represent plants in the prebloom stage with a few from the podding and pod-filling stage of growth.

C. RATEOF UPTAKE,REDISTRIBUTION, AND FERTILIZATION Insdicient data make it impossible to report on uptake rates; however, continued uptake throughout the life cycle seems essential. This absence of translocation in the plant probably necessitates a continuous supply of available iron (Brown et al., 1959). Iron chlorosis was recognized over a hundred years ago ( McMurtrey, 1938). Its positive identification was confirmed through its correction by iron fertilization. Today foliar application of iron is a common means of correcting the deficiency and is much more effective than soil application. Less-soluble iron sources (glasses) and iron chelates have proved effective in soil application; their reliability, however, varies with different soil types. Nevertheless, iron deficiencies are rather easily corrected, and it is questionable that iron is a limiting factor in the Midwest, where iron deficiency is uncommon. The inactivation of iron in the plant by calcium and phosphorus inducing quasi-iron deficiency, which could limit yield, is a distinct possibility. X. Manganese

A. CONCENTRATIONS IN T H E PLANT A hundredfold range (0.1 to 10.0 p.p.m.) in the manganese concentration of the nutrient solution resulted in a fiftyfold range in the manganese concentration in the plant (40 to 2200 p.p.m. ) (Morris and Pierre, 1949). Other legumes in this study showed a similar relation

MINERAL NUTRITION OF SOYBEANS

255

between plant and substrate content. This relation extended over the deficient and toxic range for soybeans which were harvested after 33 days’ growth. Ouellette (1951) also points out that the rate of manganese absorption is proportionate to its concentration in the nutrient solution. This dependence seems also to be reflected in soil-grown beans, Data on the various plant parts at different stages of growth are scant. Mature soybeans from two plots from each of four of the Illinois experimental fields were analyzed by Snider (1943). The ranges in manganese concentrations in parts per million were: roots, 12 to 220; stems, 7 to 69; leaves, 98 to 825; hulls, 13 to 161; and beans, 14 to 85. Manganese-54 used in nutrient culture-grown beans harvested after 3 weeks of growth showed that the manganese accumulated in the mature leaves, The upper stem was twice as active as the lower stem, and both were much lower than the mature leaves. The level of manganese in the solution is not reported, but the distribution would indicate an ample supply (Romney and Toth, 1954). Composite samples of all the leaves of field-grown chlorotic and nonchlorotic plants analyzed weekly by Meyer (1953) in Indiana indicated a gradual increase in manganese concentration in both groups. This probably was associated with increased supply rather than increased need. The ranges for the chlorotic and nonchlorotic plants were 14 to 27 and 24 to 49 p.p.m., respectively. Steckel (1946), also in Indiana, found 12 to 219 p.p.m. in the tops of plants in the pod-forming stage in a manganese fertilization experiment. The foliar symptoms and yields indicated a threshold value between deficient and healthy beans of 15 p.p.m. Mederski and Wilson (1955) found a similar value on analyzing chlorotic and nonchlorotic leaves of field-grown beans 83 days old. The total tops ranged from 9 to 22 pap.m. In a later study, twenty-five survey leaf samples were categorized on the basis of manganese content and chlorosis into severe chlorotic, with less than 20 p.p.m.; moderate chlorotic, with 20 to 40 p.p.m.; and nonchlorotic, over 40 p.p.m. in the topmost mature leaf of plants in the early bloom stage. Sixty-seven survey samples collected in 1958 in Indiana ( Wilkinson, unpublished, 1958) ranged in manganese content from 4 to 256 p.p.m. Leaflet and petioles from the third, fourth, and fifth nodes from plants in early podding to almost mature plants were included in the sample. This range is similar to those found in soybean tops (bloom stage) harvested from twenty New Jersey soils in outdoor cylinders (Romney and Toth, 1954). In a factorial test of four soil pH levels and manganese added with and without other minor elements, the range was 90 to 2050 p.p.m. The high concentration was obtained on the soil with a pH of 4.6, with copper added.

256

A. J. OHLROGGE

These numerous analyses would indicate that concentrations of 20 p.p.m. or less in the leaf or total plants might be a threshold value for deficiency. The minimal value appears to be less than 5 p.p.m. and the maximal values under conditions of toxicity in excess of lo00 pap.m. An adequate level probably lies between 30 and 200 p.p.m.

B. RATEOF UPTAKE, REDISTRIBUTION, AND FERTILIZATION Analyses of leaves taken weekly by Meyer (1953)indicate that rapid changes occur in manganese accumulation in the leaves both of the normal and deficient plant. This is undoubtedly a reflection of the complex factors influencing manganese availability and uptake from the soil. The appearance of manganese deficiency in the youngest tissue suggests little movement from the older tissue. The precedence of the younger tissue over older is indicated by the continued chlorosis of older leaves with the appearance of nonchlorotic green leaves as manganese is made more available. The translocation of inorganic manganese to new tissue is demonstrated by painting a leaf with tagged MnS04 and tracing the upward movement of manganese from the point of application to regions of active growth (Romney and Toth, 1954). Fertilization of beans grown on manganese-deficient soils has been practiced for over fifty years. Both foliar application and band application of manganese mixed with fertilizer are effective, but broadcast applications appear to have little value. XI. Boron

Young bean plants grown in nutrient cuItures containing 20 p.p.m. B can accumulate enormous amounts of boron (2669 p.p.m.). At 5 p.p.m. the plants contained 627 p.p.m., whereas the greatest weight was obtained with a substrate concentration of 0.25 p.p.m. B and 41 p.p.m. B in the plant. Usual boron concentrations are less than 100 p.p.m. with only small differences between or within the plant parts in various stages of growth (Hodgkiss et al., 1942). Leaf tissues containing 14 p.p.m. B showed severe boron deficiency symptoms when grown under long days; however, less vigorous shortday plants with the same boron concentration showed no deficiency symptoms, indicating a lower requirement with shorter day length (MacVicar and Struckmeyer, 1946). The plants grown on plus boron cultures contained from 59 to 64 p.p.ni. for the 34-,48-, and 68-day growth periods, respectively. Evans et al. (1950) found a high of 150 p.p.m. boron in the middle leaflets of beans grown in solutions with boron at toxic levels. Harvest was at full bloom. The “normal” concentrations were 20 p.p.m. in the lower and 24 p.p.m. in the upper leaves.

MINERAL NUTRITION OF SOYBEANS

257

Soybeans grown in Kentucky (Hodgkiss et al., 1942) and sampled on July 5, July 19, and August 4 from plots receiving 0, 5, 10, and 15 pounds B per acre applied in the row contained 14 to 31 p.p.m. B in the stems, 52 to 100 p.p.m. in the leaves, and 28 to 59 p.p.m. in the growing tip, respectively. No deficiency symptoms or yield increases were obtained. Seventeen survey samples of total tops in Indiana ranged from 24 to 51 p.p.m. B, most plants being in full bloom (Volk, 1951). The boron contents found in a later survey of sixty-eight samples of the third, fourth, and fifth leaflets and petioles ranged from 25 to 118 p.p.m. Total plant samples from a minor element experiment on Plainfield sand in Indiana ranged from 14 to 92 p.p.m. B. Later leaf and petiole samples from the seventh and eighth nodes of this same experiment analyzed 16 to 37 p.p.m. B. There were significant growth and yield increases to boron applied in the row on this soil ( Wilkinson, unpublished, 1958). The limited data indicate a close relationship between the boron contents of the substrate and the plant. The extremes in the plant range from less than 10 to over 2000 p.p.m. with concentrations between 20 and 100 p.p.m., indicating apparently normal nutrition. Although no sharp lines exist between deficiency and adequacy, 16 to 20 p.p.m. represent the transition zone. Boron deficiency in soybeans, although uncommon, is easily corrected by broadcast applications of borax.

XII. Zinc The data indicate a near tenfold range in zinc concentrations in soybean plants when age and plant part are disregarded. The Indiana survey samples ranged from 10 to 90 p.p.m.; the 1958 whole-plant samples, from 11 to 25; and the latter leaflet petiole samples, from 11 to 24 p.p.m. ( Wilkinson, unpublished, 1958). Viets et al. ( 1954) analyzed two samples of the youngest mature leaflet and petiole of plants growing on zincdeficient and nondeficient soils and found 16.3,16.4, and 19.1, 24.3 p.p.m., respectively. The threshold value probably lies between these limits; in the greenhouse 34-day-old plants growing on zinc-deficient soil analyzed 27.2 p.p.m. Zinc additions increased the concentration to 45.0 p.p.m. A zinc-deficient Blackbelt soil produced soybean tops containing 15 p.p.m. of zinc whereas the normal soil soybeans analyzed 30 p.p.m. (Nelson, 1956). Kentucky analyses of thirty-two samples of hay as reported by Beeson (1941) ranged from 27 to 80 p.p.m. In a greenhouse study of zinc chelation in soils, soybeans harvested at 2,3,4, 6, and 8 weeks had a maximum zinc content of 250 p.p.m, and a minimum of 50 p.p.m. All soils were high in zinc (Miller and Ohlrogge, 1958).

258

A. J. OHLROGGE

The appearance of the most severe deficiency symptoms on the oldest leaves (Viets et al., 1954) suggests redistribution of zinc in the plant. Folier spray and band application in the soil have proved effective in correcting the deficiency. XIII. Copper and Other Elements

The responsiveness of crops on peat and muck soils of the Everglades and other areas to copper additions has been recognized for over thirty years. Likewise the correction of citrus die-back with copper is an established practice of long standing. Five varieties of soybeans were included in the Florida test of 1925 (Allison et al., 1927). Tremendous responses with differences between varieties were obtained. No copper analyses of the crop were reported. Few additional studies of copper fertilization were subsequently reported, partly because commercial soybean production is largely confined to mineral soils. The analyses of thirty-two soybean hay samples by McHargue (1925) gave a range in copper contents from 4 to 12 p.p.m. The Indiana survey ( Wilkinson, unpublished, 1958) leaf samples ranged from 6 to 26 p.p.m. and VOWS (1951) 17 total-plant samples analyzed 7 to 24 p.p.m. The samples of total plants in early bloom collected in a minor element study analyzed 19 to 33 p.p.m. Later leaf samples ranged from 4 to 9 p.p.m. Statistically significant ( 1 per cent) responses in growth and grain yield were obtained to CuS04 applied in the mixed fertilizer band at planting ( Wilkinson, unpublished, 1958). The role of molybdenum in nitrogen nutrition is discussed in the following chapter on soybean physiology. Chlorine, an essential nutrient, has not been studied in relation to soybean nutrition. The role of the heavy metals has been investigated, principally by Warington ( 1954). The relationships she has pointed out are not believed to be significant in soybean nutrition in the field. XIV.

The Future of Soybean Nutrition

The ineffectiveness of direct soybean fertilization in consistently increasing soybean grain yields was one problem that helped to bring this review into existence. The body of the review attempted to establish, or suggest, some cardinal nutrient concentrations in plants which define levels of nutrition, and thereby to aid the agronomist to determine and understand the limiting factors in his fertilization experiments. A second motivating factor was the small apparent increase in the United States during the past twenty years in the average yield per acre of soybeans as compared to corn, which competes for the farmer's inter-

MINERAL NUTRITION OF SOYBEANS

259

tilled crop acreage. A linear regression analysis for the 1939 to 1959 period indicates corn yields per acre increased 1.00 bushel per year whereas soybean yields increased only 0.25 bushels per acre per year. The r values were 0.88 and 0.68 for corn and soybeans, respectively, At the beginning of the period, soybean yields were 62 per cent of the corn average; and at the end of the period, they were 47 per cent of the per acre yield of corn. These percentages were calculated from the regression lines. The great increase in corn yields cannot be ascribed alone to increased use of production know-how on the farm. There has also been a marked shift in the corn acreage, but the total acreage has remained fairly constant. The decrease in the corn acres in the low-yielding Southern and Southeastern States has been replaced in part with high-yielding irrigated acres in the West. The opposite is true for soybeans. The fivefold increase in total soybean acreage in the United States was in part made up of the new, low-yielding acreage in the Southeast. The results of varietal improvement through breeding, started much later than corn, are most evident in the remarkable recent increase in the average yields in this area. The new, high-yielding, adapted diseaseresistant varieties have helped make possible recent State average yields in several Southern States about equal to those in the older soybeangrowing states. In these States, such as Indiana and Illinois, soybean State average yields have been consistently about 40 per cent of the corn yields. This percentage was also found for the five countries in each state with the highest and lowest average per acre yield. No significant deviations from this 40 per cent figure were found, indicating that soybeans have increased percentagewise in yield as much as corn. The direct cause for the soybean increase cannot be precisely determined since a host of factors contribute to the final yield of a crop. However many of the factors responsible for the corn increases must also have had a beneficial effect on soybeans. These comparisons between two competitive crops indicate that on a national, State, and county basis soybeans have made gains equal to those of corn when allowance is made for the shift in acreage for these crops. In spite of the fine record and bright future for soybeans, there remains the problem of why soybeans do not positively respond to direct fertilization. The discussions on each of the mineral nutrients indicate that absorption by the crop is not a serious problem. Then why cannot the agronomist easily prescribe treatments that will immediately double or triple a 20-bushel per acre soybean yield, when he is able to do this

260

A. J. OHLROGGE

for a 50-bushel per acre corn yield? Researches along the following lines hold greatest promise for bringing understanding to the problem: 1. Soybeans are a new crop to the United States. Cultural techniques used by the farmer, and too often by the agronomist in field research, are those that fit his convenience rather than those that are best for the crop. Corn equipment is used almost exclusively and rows are too wide apart for maximal yields. Sometimes the soil pH in a fertilizer experiment is not ideal for soybeans. These are conditions that may explain some of the nonresponsiveness in fertilizer experiments. It should be worthwhile to re-examine nonresponsive situations with experiments where all controllable growth factors are maintained at an optimum. 2. Spectrographic or X-ray fluorescence analytical methods, multiple regression, and electronic computers are powerful tools that have not been used in soybean nutrition studies, but might be applied to data from survey field samples. The samples would be made up of plant parts harvested at those critical periods that best reflect the nutrient status of the plant. It is widely recognized that in the highly organized life of the plant, there are complex nutrient interactions that influence plant growth. Improved statistical methods make possible quantitative evaluation of the contribution of each factor. As an example, in a study of the mechanism of dwarfing of apples caused by an intergraft of dwarfing stock, it was found in a multiple regression analysis that between 90 and 95 per cent of the variation in growth and yield could be accounted for by the nitrogen, potassium, calcium, phosphorus, and magnesium composition of the leaf samples (Klein, 1960). Simple correlations of single factors were insignificant. Although such studies do not differentiate causes and effects, intelligent interpretation of the results usually makes this possible. The occasional depressing effects of phosphate fertilization, not unique with soybeans, holds promise of easy solution with these analytical tools. 3. Photosynthetic activity is basic to dry matter accumulation. Detailed studies on day-to-day dry matter accumulation are costly and time consuming. It is believed, however, that critical low-cost experiments in this area can be devised, the results of which would be most rewarding. Shade-leaf removal, for example, might have startling effects on grain yields. Shading experiments during critical growth periods might likewise give revealing clues to the limiting factors in soybean production. 4. Nutrient-withdrawal experiments would seem to be able to provide the information necessary for diagnosing mineral-nutrition problems. Such experiments must not only establish critical periods, but also establish what concentrations in which plant parts best define nutritional levels. For example, calcium nutrition studies may reveal the solution to

MINERAL NUTRITION OF SOYBEANS

261

the soybean problem, as they have significantly contributed to the solution of the peanut fertilization problem. 5. Fertilizer can either be broadcast or band applied, but preference is for band application. It is important, therefore, that the physical, chemical, and biological conditions in the fertilized soil zone be defined. This will make possible the next step in developing an understanding of nutrient uptake that will enable the maintenance of optimal nutrient concentration in the plant. 6. Soybean improvement through breeding is closely related to mineral nutrition. As the physiological basis for varietal improvement is uncovered, concomitant understanding will come in mineral nutrition. REFERENCES Allen, D. I. 1943. Missouri Uniu. Agr. Expt. Sta. Research Bull. No. 361. Allison, R. V., Bryan, 0. C., and Hunter, J. H. 1927. Florida Uniu. Agr. Expt. Sta. Gainesuille Bull. 190. Allos, H. F., and Bartholomew, W. V., 1959. Soil Sci. 87, 61-66. Austin, R. H. 1930. J. Am. SOC. Agron. 22, 136-156. Beeson, K. C. 1941. U. S . Dept. Agr. Misc. Publ. No. 569. Beeson, K. C., Gray, L., and Hamner, K. C. 1948. J. Am. SOC. Agron. 40, 553-562. Biddulph, O., and Woodbridge, C. G. 1952. Plant Physiol. 27, 431-444. Blackman, G. E., and Black, J. N. 1959. Ann. Botany (London) 23, 131-145. Borst, H. L., and Thatcher, L. E. 1931. Ohio Agr. Expt. Sta. Bull. No. 494. Brown, D. A., and Albrecht, W. A. 1947. Soil Sci. SOC. Am. Proc. 12, 342-347. Brown, J. C., Holmes, R. S., and Tiffin, L. 0. 1958. Soil Sci. 86, 75-82. Brown, J. C., Ti& L. O., Holmes, R. S., Specht, A. W., and Resnicky, J. W. 1959. Soil Sci. 87, 89-94. Bureau, M. F., Mederski, H. J., and Evans, C. E. 1953. Agron. 1. 46, 150-154. Camery, M. P., and Weber, C. R. 1953. Iowa Agr. Expt. Sta. Research Bull No. 800.

Duncan, W. G., and Ohlrogge, A. J, 1958. Agron. J . SO, 605-608. Eaton, S. V. 1935. Botan. Gaz. 97, 68-100. Erdman, L. W. 1929. J. Am. SOC. Agron. 21, 361-366. Erdman, L. W., and Means, U. M. 1952. Soil Sci. 75, 231-235. Evans, C. E., Lathwell, D. J., and Mederski, H. J. 1950. Agron. J . 42, 25-32. Graham, E. R.,and Turlay, H. C. 1947. Soil Sci. SOC. Am. Proc. 12, 332-335. Graham, E. R., Powell, S., and Carter, M. 1956, Missouri Uniu. Agr. Expt. Sta. Research Bull No. 607. Hammond, L. C., Black, C. A., and Norman, A. G. 1951. Iowa Agr. Expt. Sta. Research Bull. No. 584. Hampton, F. E., and Albrecht, W. A. 1944. Missouri Uniu. Agr. Expt. Sta. Research Bull. No. 581. Harston, C. B., and Albrecht, W. A. 1942. Soil Sci. SOC. Am. Proc. 7, 247-257. Hashimoto, T. 1953. J. Sci. Soil Manure Japan 24, 51-53. Hashimoto, T. 1955a. Soil and Plant Food (Tokyo) 1, 31-32. Hashimoto, T. 195%. J. Sci. Soil Manure Japan !B, 139-142. Hashimoto, T.,and Okamoto, M. 1954. J . Sci. Soil Manure Japan 24, 281-282. Hawkes, G. R. 1957. Dissertation Abstr. 17, 2754-2756.

262

A. J. OHLROGGE

Hodgkiss, W. S., Hageman, R. H., and McHargue, J. S. 1942. Plant Physiol. 17, 852-880. Hopkins, E. F.,Pagan, V., and Silva, F. J. R. 2944. J. Agr. Uniu. Puerto Rko 28, 43-101. Hutchings, T. B. 1938. Missouri Agr. Research Bull. No. a49. Klein, R. A. 1980. Ph.D. Thesis, Purdue University, Lafayette, Indiana. Krantz, B. A., Nelson, W. L., Welch, C. D., and Hall, N. S. 1949. Soil Sci. 68, 171-177. Lathwell, D. J., and Evans, C. E. 1951. Agron. J. 43, 284-270. Lyons, J. C., and Earley, E. B. 1952. Soil Sci. SOC. Am. Proc. 16, 259-283. McAlister, D.F., and Krober, 0. A. 1951. Plant Physiol. 26, 525-538. McGeorge, W. T. 1949. Soil Sci. 68, 381-398. McHargue, J. S. 1925. J. Agr. Research 30, 193-198. McMurtrey, J. E., Jr. 1938. Botan. Reu. 4, 183-203. MacVicar, R., and Struckmeyer, B. E. 1948. Botan. Gaz. 107, 454-481. Matrone, G., Smith, F. H., Weldon, V. B., Woodhouse, W. W., Peterson, W. C., and Beeson, K. C. 1954. U.S . Dept. Agr. Tech. Bull. No. 1088. Mederski, H. J. 1950. Ph.D. Thesis, Ohio State University, Columbus, Ohio. Mederski, H. J., and Wilson, J. H. 1955. Soil Sci. SOC. Am. Proc. 19, 481-484. Mederski, H. J., Wilson, J. H., and Vok, G. W. 1958. Ohio Agr. Expt. Sta. Research Circ. No. 69. Meyer, W. J. 1953. M.S. Thesis, Purdue University, Lafayette, Indiana. Miller, M. H., and Ohlrogge, A. J. 1958. Soil Sci. SOC. Am. Proc. 22, 228-231. Morris, H. D., and Pierre, W. H. 1949. Agron. J. 41, 107-111. Morrison, F. B. 1958. “Feeds and Feeding.” Morrison Publishing Co., Ithaca, New York. Moser, F. 1943. Soil Scf. SOC. Am. Proc. 7, 339-344. Muhr, G. R. 1940. Soil Sci. SOC. Am. Proc. 6, 220-228. Mumeek, A. E. 1937. Missouri Uniu. Agr. Expt. Sta. Research Bull. No. 268. Nelson, L. E. 1958. Soil Sci. 82, 271-274. Nelson, W. L. 1948. North Carolina Research and Farming No. 4, 4-5, 9. Nelson, W. L., Burkhardt, L., and Colwell, W. E. 1945. Soil Sci. SOC. Am. Proc. 10, 224-229. Ohlrogge, A. J. 1958. Plant Food Rev. 4 ( 3 and 4 ) , 4, 5, 33-35. Olson, C. 1938. Compt. rend. trav. lab. Carkiberg Sbr. chim. 21, 301-313. Oserkowsky, J. 1933. Plant Physbl. 8, 449-468. Ouellette, G. J. 1951. Sci. Agr. 91, 277-285. Romney, E. M., and Toth, S. J. 1954. Soil Sci. 77, 107-117. Siegel, J. J., Hough, H. W., and Turk, L. M. 1952. Soil Sci. SOC. Am. Proc. 16, 185-188. Snider, H. J. 1943. Soil Sci. 66, 187-195. Somers, I. I., and Shive, J. W. 1942. Plant Physiol. 17, 582-802. Spector, W. S. (ed. ) 1958. “Handbook of Biological Data.” Saunders, Philadelphia, Pennsylvania. Steckel, J. E. 1948. Soil Sci. SOC. Am. Proc. 11, 345-348. Takeshima, H. 1952. Crop Sci. SOC.Japan Proc. 21, 119-120. Togari, Y., Kato, Y., and Ebata, M. 1955. Crop Sci. SOC. Japan Proc. 24, 103-107. Vanderford, H. B. 1940. J. Am. SOC.Agron. 32,789-793. Viets, F. G., Jr., Boawn, L. C., and Crawford, C. L. 1954. Soil Scl. 78, 305-318. Volk, R. J. 1951. M.S. Thesis, Purdue University, Lafayette, Indiana.

MINERAL NUTRITION OF SOYBEANS

263

Von Ohlen, F. W. 1931. Am. J . Botany 18, 30-49. Wallace, A., and Ashcroft, R. T. 1956. Soil Sci. 82, 233-236. Warington, K. 1954. Ann. Appl. B w l . 41, 1-22. Watson, D. J., Thome, G. N., and French, S . A. W. 1958. Ann. Botany (London) 22, 321-352. Webb, J. R., Ohlrogge, A. J., and Barber, S. A. 1954. Soil Sci. SOC. Am. Proc. 18, 458-462. Weber, C. R. 1955. Agron. J . 47, 262-266. Webster, J . E. 1928. Plant Physiol. 3, 31-43. Welch, C. D., Hall, N. S., and Nelson, W. L. 1949. Soil Sci. SOC. Am. Proc. 14, 231-235. Weiss, M. G. 1943. Genetics 28, 253-268. Yoshihara, K., and Kawanshee, S. 1956. Proc. Crop Sci. SOC. Japan. 24, 228-229. Zimmerman, L. J. 1956. Ph.D. Thesis, Purdue University, Lafayette, Indiana.