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VII. Seed Quality and Seed Treatment

VII. Seed Quality and Seed Treatment

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390



JACKSON L. CARITER AND EDGAR E. HARTWIG



Grabe, personal communication ) . Soybeans germinate most rapidly at

86" F., and if in sand, the most favorable moisture level is 15 per cent

water based on dry weight of sand (Delouche, 1953). Methods of

measuring seed viability are important to the seed trade (Sprague,

1958).Price per bushel of pure live seed, calculated by dividing the price

per bushel by the purity times germination, is a simple way to determine

planting value of the seed (Everson, 1957).



B. SEEDTREATMENT

Seed treatment with a fungicide is not recommended as a general

practice when seed with high germination is planted. Stands may be

increased by seed treatment when seed having a germination of 85 per

cent or less is planted. Although seed treatment seldom results in

increased seed yields (Howard W. Johnson et al., 1954; Chamberlain and

Koehler, 1959), the improved stands resulting from seed treatment aid

in giving soybeans a competitive advantage with weeds. Studies by

Howard W. Johnson et al. (1954) show that seed may be treated at any

time between harvest and planting with equal effectiveness. The most

satisfactory time for treating seed would be as it is cleaned. The materials

Arasan, Captan, and Spergon have proved to be most satisfactory for

treatment of soybean seed. Before any lot of seed is treated, it may be

a good practice to check the germination with and without the fungicide

to determine the beneficial effect of seed treatment on each seed lot.

VIII. Nutrient Requirements



Nodulated soybeans do not respond to nitrogen fertilizer as do

non-legume crops and because of this, gained a reputation of not responding to direct fertilization, a reputation that is not justified. In order

better to understand the nutrient response of soybeans in comparison

with corn, the total energy in the protein-oil seed of soybeans has been

compared with the largely carbohydrate seed of corn (Howell, 1961).

These studies show that in terms of total energy per acre, a 45-bushel

soybean yield is equivalent to a 100-bushel yield of corn.



A. NITROGEN

REQUIREMENTS

AND NODULATION

When properly nodulated, soybean roots may derive a considerable

portion of the nitrogen needs of the plant from the nodules through the

fixation of atmospheric nitrogen. Weiss (1949) presented a detailed

review of the literature in this field, indicating the importance of nodulation to yield and composition of the crop.



THE MANAGEMENT OF SOYBEANS



391



1. Effectiveness of Nodulution as a Source of Nitrogen

A mutation type was reported by Williams and Lynch (1954) which

does not develop nodules when inoculated with the soybean nodulating

bacterium Rhizobium japonicum. This mutation, due to a single recessive

gene, has been incorporated into several nodulating and nonnodulating

near-isogenic lines of different maturities and is providing an excellent

tool for the study of nitrogen fertility problems.

Perhaps the best measures of effectiveness of nodules in supplying

the soybean plant with nitrogen are the results of studies using one of

these pairs of near-isogenic lines which differ in ability to nodulate. At

Ames, Iowa, when 20 tons of ground corncobs per acre were added to

the soil prior to planting to reduce the available nitrogen, nodulated soybeans produced 41 bushels per acre without nitrogen and 43 bushels

when 600 pounds per acre of nitrogen was added. The nonnodulated

strain produced 16 bushels per acre without nitrogen and 41 bushels with

600 pounds per acre of nitrogen. The 25-bushel yield increase for

nodulated over nonnodulated soybeans where no nitrogen was applied was

attributed to nodule activity. The 25 bushels of seed contained 96

pounds of nitrogen (C. R. Weber, personal communication). In a similar

comparison of nodulated vs. nonnodulated soybeans on Sharkey clay

at Stoneville, Mississippi, nodulated soybeans yielded at the rate of 42

bushels per acre with 41 per cent protein whereas nonnodulated soybeans

yielded at the rate of 14 bushels per acre with only 28 per cent protein.

The seed from nodulated soybeans contained 112 pounds more nitrogen

per acre than seed from nonnodulated soybeans. In the same general

area, other strains of soybeans produced seed yields as high as 60 bushels

per acre which contained 192 pounds of nitrogen per acre, or an increase

of about 160 pounds per acre over that for the nonnodulated strain.

It appears that under conditions of low available soil nitrogen, nitrogen fixation from nodulation can furnish nitrogen for soybean yields of

at least 60 bushels per acre with fixed nitrogen amounting to as much

as approximately 160 pounds per acre. On soils high in available nitrogen,

the amount of nitrogen supplied by the fixation process appears to be low.

As far back as 1900, it was noticed that nodules of legumes inoculated

with certain pure cultures were more active than those produced by

bacteria already in the soil (Erdman, 1949). Some strains of bacteria

are more efficient than others in fixing nitrogen, some are more aggressive

in nodulating roots, and some are more competitive in the soil. Means

et al. ( 1961), using a chlorosis-inducing strain of Rhizobium japonicum

and mixing it in varying proportions with other strains, found that as

little as 1.1 per cent of this strain in the mixture with another strain



392



JACKSON L. CAR-



A N D EDGAR E. HARTWIG



caused 85 per cent of the nodules on certain soybean varieties. Almost

without exception, a given nodule contains only one bacterial genotype.

A chlorosis-inducing strain has been found in the Mississippi delta area

that is aggressive on the variety, LEE, and causes typical chlorosis symptoms on plants around 6 weeks old (Clark, 1957). The symptoms are

transient-that is, they are present for a short period and then new

leaves growing out appear normal. Field observations indicate that the

bacterial strain is relatively efficient in nitrogen fixation, though for a

week or two symptoms may be alarming to a soybean grower.

2. Methods of Znoculation

The generally accepted method for applying inoculum to the seed

is to apply the bacteria adsorbed in a humus-peat carrier to slightly

moistened seed or to make up a slurry of the inoculum in water and

apply this. The quantity of seed inoculated should be limited to that

which can be planted before the seed coats have completely dried.

Results from several studies showed that 83 per cent of the inoculant

was retained upon moistened seed whereas only 8 per cent of the inoculant was retained upon dry seed (Clark, 1956). Recent studies with

precoating of soybean seed have shown no advantage over traditional

methods of inoculation.



3. Survival of Bacteria in the Soil

Studies in Illinois showed good survival of bacteria in soils that

had not grown a crop of soybeans in thirteen years (Lynch and Sears,

1952). Similar results were obtained in North Carolina after twelve

years of continuous cotton. Noninoculated plots were well nodulated

and produced yields similar to yields of inoculated plots (E. E. Hartwig,

unpublished).



4. Effect of Seed Treatment on Inoculation

Under some conditions, seed treatment with the organic fungicides

Arasan, Captan, or Spergon will result in improved stands of soybeans.

Since rhizobia are already present in most soils in older soybean-growing

areas, it is difficult to assess the effect of seed treatment upon survival

of rhizobia. In 1950, planting were made on newly cleared land at the

West Florida Experiment Station using ROANOKE seed which had been

untreated or treated with Arasan or with Spergon. Both Arasan and

Spergon reduced the effectiveness of inoculation. Seed yields from nontreated, inoculated seed were 22 bushels per acre as compared with 7

bushels for noninoculated seed and 13 bushels each for seed treated with

Arasan or Spergon and inoculated (E. E. Hartwig, unpublished).



THE MANAGEMENT OF SOYBEANS



393



5. Effect of Nitrogen Applications

Applications of nitrogen tend to retard nodulation of seedinoculated soybeans planted in rhizobia-free soil. Applications of

100 pounds of nitrogen at planting time in the Imperial Valley of California, where rhizobia were not present in the soil, resulted in poorly

nodulated soybeans which produced yields of 6 to 16 bushels per acre

with 27 to 34 per cent protein on a dry matter basis. Omitting nitrogen

application at planting time permitted good nodulation and resulted

in yields of 35 to 40 bushels per acre with normal protein content of

the seed (G. H. Abel, Jr., personal communication).

An extensive field trial in Arkansas in which nitrogen was applied

in a factorial experiment with phosphorus and potassium showed no

significant response from nitrogen applied at different stages of plant

development (Hardy, 1959). These results are typical of the many trials

showing no appreciable benefit from nitrogen fertilizer on well-nodulated

soybeans.



B. LIMINGAND PH LEVELS

1. p H and Plant Development

There seems to be general agreement that a pH of 6.0 to 6.5 is desirable for soybean production (P. R. Smith, 1956). In North Carolina,

under conditions where the pH of the soil was 4.2, nitrogen-fixing bacteria

could not function actively and a yield response was obtained from added

nitrogen. With additions of lime, soybean yields were related rather

closely to the degree of calcium saturation regardless of the sourcecalcitic or dolomitic. On two soils, CaS04 had a detrimental effect due

to the toxic effect of the sulfate ion and the salt injury (Welch and

Nelson, 1950). In another series of soil treatments in North Carolina, a

2.8-bushel increase resulted from lime alone, and a 7.2-bushel increase

from lime plus phosphate and potash (Collins et al., 1947). The pH of

these soils before liming ranged from 5.1 to 6.0.

A Richton silt loam in Arkansas with an initial pH of 4.9 produced

significantly higher seed yields after applications of 4 and 8 tons of

dolomitic limestone (Parks et al., 1959).

Soils in some areas have shown a tendency to be short of magnesium,

a minor element that is essential to green chlorophyll formation in leaves.

Magnesium and calcium must be in proper balance for best growth.

Surface applications of lime have been shown to move slowly

downward in the soil under humid conditions; thus, there is relatively

little advantage to deep placement by mechanical means. For a given soil



394



JACKSON L. CAR'ITER AND EDGAR E. HARTWIG



and climate, the rate and h a 1 depth of effect are functions of the amount

applied and the time elapsed (Brown et aZ., 1956).

2. Calcium and Magnesium Requirements

A soil in Illinois, with a pH of 4.1 and an exchangeable magnesium

level of 60 to 75 pounds per acre, gave increased yields of both corn

and soybeans from applications of 75 to 150 pounds of magnesium per

acre or 2 tons of dolomitic limestone (Key and Kurtz, 1960). The authors

considered a level of 150 pounds per acre of exchangeable soil magnesium to be adequate for field crops on soils of moderate to low exchange capacity.

A North Carolina soil low in magnesium showed a 4-bushel yield

response from 60 pounds of magnesium (Nelson et al., 1945).

A survey of farmer's fields in south Alabama showed that most fields

which appeared to be low in vigor had a p H of 4.9 or lower and/or

the available calcium below 200 pounds per acre. Soils with pH as low

as 4.4 and calcium as low as 120 pounds per acre were observed. Many

of these soils were also low in magnesium. A soil with a pH of 4.8

limed to give a pH of 6.2 gave a yield response of from 14 to 31 bushels

per acre when adequate potassium was supplied (Rouse, 1961).

C. PHOSPHORUS

Approximately 16 pounds of phosphorus are present in 40 bushels

of soybean seed. North Carolina results indicated that a yield response

was obtained from applied phosphorus when their soil test showed less

than 40 pounds available phosphorus in the soil (C. D. Welch, personal

communication). Nelson ( 1946), on a coastal plain soil in North Carolina,

obtained 6.4 bushels p e r acre of soybeans on a soil low in available

phosphorus, but 33.8 bushels with added phosphorus. Response curves

have been drawn by Bray (1961) which show that with 10 pounds of

available phosphorus per acre soybean yields will be 75 per cent of the

maximum expected, whereas with 30 pounds of available phoshoms

soybean yields will be at 98 per cent of maximum. This response to

phosphorus assumes other elements to be in adequate supply. The

response curve for soybeans is almost identical with that for corn

(Fig. 8).

LINCOLN

soybeans were grown on a Wooster silt loam in Ohio at soil

phosphorus levels of 53, 30, and 11 pounds per acre. The percentage of

total phosphorus derived from fertilizer was inversely related to the

level of soil phosphorus. When radioactive superphosphate was applied,

the plants near maturity had obtained about 25 per cent of their phos-



THE MANAGEMENT OF SOYBEANS



395



phorus from the fertilizer on the high phosphorus soil and nearly 60 per

cent on the low phosphorus soil. The high and medium levels of soil

phosphorus gave increases in total dry matter of 38 per cent and 9 per

cent over the low level, but all seed yields were at a 32-bushel level

(Bureau et al., 1953). These results suggest that some other factors were

limiting seed production, since North Carolina experiments on a low

phosphorus soil showed grain : straw ratios to be relatively constant when

additional phosphorus was added.



FIG.8. Relation of available phosphorus to percentage of maximum yield of soybeans and other crops. (From Bray, 1961.)



The availability of all the essential elements obtained by plants from

the soil is affected in some way or another by the reaction of the soil.

Phosphorus in particular becomes less available as the pH value drops

below 6.5. This result may be due to the interaction of phosphate with

hydrated iron oxides to form a basic iron phosphate (Truog, 1938;

Klemme, 1949; Pearson, 1958).

In a sand nutrient culture, the removal of magnesium did not retard

phosphorus absorption, but did have a significant effect on the movement and final location of phosphorus in the plant, resulting in a higher

percentage of phosphorus in the vegetative parts and a lower percentage



396



JACKSON L. C A R T E R AND EDGAR E. HARTWIG



in the seeds. Thus, according to Webb et al. (1954), magnesium may

function as a carrier of phosphorus in the plant.

The ratio of phosphorus to potassium may be as important in some

cases as the phosphorus level. Miller et al. (1961a, b), on a Dickinson

fine sandy loam in Iowa with a pH of 6.6 and testing low in available

phosphorus and very low in available potassium, showed that over 80

per cent of the variation in soybean yield which they obtained was accounted for by the variation in phosphorus and potassium content of

some plant parts. The greatest yield increase was obtained from heavy

applications of both phosphorus and potassium, but the greatest yield

depression resulted from heavy additions of phosphorus and no addition

of potassium. The variety they were using in the study (HAROSOY) is

sensitive to high levels of phosphorus in relation to other elements in

the nutrient solution.

Howell (1954) found an increase in relative growth of soybeans as

phosphorus level was increased from 2 parts per million (ppm) to 10

in the nutrient solutions, but a marked difference in varietal response to

a wider range in phosphorus level. At levels as high as 112ppm, the

variety CHIEF responded favorably in growth but LINCOLN showed definite

symptoms of phosphorus toxicity. Howell and Bernard (1961) have

classified commercial varieties with respect to phosphorus response.

Weiss (1943) modified iron chlorosis by changing phosphorus level

in the nutrient solution, but the iron inefficient character does not appear

to be closely related to the phosphorus toxicity reported by Howell.



D. PoTAssNht

Forty bushels of soybean seed will contain approximately 50 pounds

of potassium. North Carolina data suggest that response to applications

of potassium is likely when the available soil potassium is less than 75

pounds per acre ( C. D. Welch, personal communication). Response

curves drawn by Bray (1961) suggest that when the soil test shows 50

pounds of potassium per acre the soybean yield will be approximately

50 per cent of the maximum whereas with a soil test of 200 pounds, the

soybean yield will be at 97 per cent of maximum (Fig. 9). As with

phosphorus, the expected response curve for soybeans closely approximates that for corn.

On a Kalmia sandy loam in Alabama high in phosphorus but low in

potassium, the five-year average yield increase from 50 pounds of

potassium was 50 per cent (Rouse, 1961). Studies in North Carolina on

a soil very low in potassium showed a fourfold yield increase from

potassium. The addition of potassium caused greater retention of pods,

increased the degree of pod filling, and improved seed quality. The



THE MANAGEMENT OF SOYBEANS



397



application of 120 pounds per acre of potassium on this poor soil also

increased oil content about 2 per cent and reduced protein content

5 per cent (Nelson et al., 1945).

Indiana soybeans grown in rotation with corn and wheat gave equal

response to row or broadcast applications of potassium. The response was

proportional to the potassium applied and was closely correlated with

rainfall during the growing season (Barber, 1959).



FIG.9. Relation of available potassium to percentage

beans and other crops. (From Bray, 1981.)



of maximum



yield of soy-



The abilities of peanuts, soybeans, corn, and cotton to absorb

potassium in small volumes of Ruston fine sandy loam were compared

in the greenhouse by Reid and York (1955). Peanuts, soybeans, and

corn absorbed essentially equal amounts of potassium, but cotton

tended to absorb slightly more under low potassium conditions. Potassium

deficiency symptoms appeared first and were most severe on corn

followed by cotton, soybeans, and peanuts. All four crops responded in

dry matter production to the application of potassium. In a second

cropping, the dry matter production in unfertilized soil for peanuts,

soybeans, cotton, and corn was 69, 85, 45, and 20 per cent, respectively,

of the plants fertilized with potassium.



398



JACKSON L. CARTIER AND EDGAR E. HARTWIG



Soybean seed is very sensitive to soluble-salt injury during germination, so potash should not be drilled directly with the seed. Placement

studies show best results are obtained from band placement 2 inches to

the side and 2 inches below the seed.

When studying cation uptake, the soil temperature is important.

Wallace (1957) found that the potassium content of soybeans increased

with temperature to 90"F., but the potassium in barley increased from

54" F. to 72" F. and decreased from 72" to 90".



E. TRACE

ELEMENTS

In addition to calcium, magnesium, potassium, phosphorus, and

nitrogen, several other elements are essential for satisfactory development of the soybean plant. The elements iron, manganese, cobalt, sulfur,

boron, zinc, copper, and molybdenum are usually present in adequate

quantities, but soils occur in which one or more of these materials might

limit crop production.

The visible sign of iron deficiency in the soybean is a yellowing or

chlorosis of the leaves. Iron is required for chlorophyll synthesis and

respiration. In most soils the iron supply is adequate and conditions are

generally favorable for its absorption by soybean plants. Iron deficiency

symptoms are generally observed only on soils with a high pH and a

high calcium carbonate content. Weiss (1943) observed a differential

response of soybean varieties growing on a calcareous soil in Iowa.

Iron deficiency can be corrected by spray applications of ferrous sulfate.

Manganese, like iron, aids in the formation of chlorophyll. Manganesedeficient soybeans have a light green to yellow mottling between leaf

veins, Manganese deficiency symptoms are most likely to occur when soybeans are grown on soils limed to near the neutral level. According to

Ohlrogge (1950),low levels of available manganese in soils are associated

with a soil pH of above 6.3 on soils that have developed under a high

water table. This condition encourages the reduction of the manganese

to the soluble form which is consequently leached from the soil.

Manganese sulfate has been found to be more effective than manganese

oxide for correcting manganese deficiency in soybeans (Mederski et al.,

1960). Low soil temperature combined with high soil moisture was

conducive to the development of severe foliar symptoms of manganese

deficiency.

The relatively short time required for leaves to accumulate high

concentrations of manganese probably accounts for the effectiveness of

manganese sprays applied under a variety of field conditions. Manganese

can be applied dry at a rate of 25 pounds or more of manganese sulfate

per acre at planting time or as 10 pounds of manganese sulfate in 15



THE MANAGEMENT OF SOYBEANS



399



gallons of water per acre as soon as deficiency symptoms appear.

Repeated yearly applications of manganese are needed on fields where

this trace nutrient is known to be deficient. Manganese applied to the

soil changes to an unavailable form during the growing season (Mederski

and Jones, 1961).

Plant species and varieties differ in their capacity to take micronutrients from the soil. Studies at North Carolina showed that OGDEN

soybeans took up only 114 ppm of manganese from a field where LEE

soybeans in an adjacent row took up 197ppm.

Molybdenum, unlike manganese, boron, iron, copper, and zinc,

becomes increasingly available as the soil pH is raised (Reid et al., 1960).

Molybdenum is needed by the plant and in the symbiotic fixation of

nitrogen or in the reduction of nitrate (Anderson and Spencer, 1950;

Evans, 1956). Soils in need of molybdenum are quite rare in the United

States. Parker and Harris (1962), working in Georgia on a soil with a

pH of 5.6, obtained yield responses from applications of 0.2 pound

molybdenum per acre equivalent to applications of 2 tons of limestone.

The application of molybdenum further increased protein content of

the seed on a limed soil. Untreated plots yielded at the rate of 30

bushels per acre, but with the addition of molybdenum or limestone,

yields of 50 bushels were produced. Caution should be observed by

applying molybdenum only to soils that are deficient in this element, as

plants may accumulate levels that are toxic to animals (Stout and

Johnson, 1957).

Cobalt is accumulated from the soil by plants, which in turn become

the primary source of cobalt for animals. While cobalt is essential for

animals and for synthesis of vitamin B12, plant needs are met by as little

as 1part per billion in nutrient solutions. One part per million produced

toxic symptoms and resulted in growth reduction (Toth and Romney,

1954). In many field trials in the Midwest, as little as 2.5 g. of cobalt

applied on a bushel of soybean seed at planting time caused observable

toxic symptoms on the unifoliate leaves (A. J. Ohlrogge, personal communication). If cobalt is applied to soil to enrich the resulting crop for

animal feeding, extreme care should be exercised not to apply toxic

smounts.

Sulfur, essential to plant life, is a part of methionine and other amino

acids in protein and also occurs in the vitamins thiamine and biotin.

According to Baxter (1952), aside from functioning as a building material,

sulfur is important in formation of chlorophyll and holds essential

elements such as iron and manganese in solution. The average sulfur

content of soybeans is about 0.16 per cent. Sulfur requirements of soybeans have been found to be lower than for cotton (Kamprath et al.,



400



JACKSON L. CAR-



AKD EDGAR E. HARTWIG



1957). It usually enters the plant from the soil as the sulfate ion, and

on most soils, especially those fertilized with superphosphate, the sulfur

supply is adequate for the needs of the plant.

Boron is essential to normal cell division and growth and the general

metabolism of plants (Russell, 1957). In a few instances, yield increases

have been obtained from boron application (S. R. Wilkinson, personal

communication), but usually a soil that grows good alfalfa has adequate

‘loron for soybeans. Boron deficiency occurs at higher boron levels in

the presence of high calcium levels (Reeve and Shive, 1944). Boron

deficiency in soybeans is easily corrected by light applications of borax,

but treatments should be made with caution as high levels of the element

are toxic to the plant (Mederski and Jones, 1961). Boron toxicity decreases with increasing concentration of calcium ( Berger, 1949).

Zinc is essential for soybeans, though needed in very small amounts

(Seatz and Jurinak, 1957). Zinc deficiency produces a light brownishyellow color to the leaves. The symptoms are more severe in cold, wet

weather, disappearing in warmer sunny weather. Where symptoms are

severe, yield may be severely reduced (Weldon and Chesnin, 1959).

Apparently, zinc is readily redistributed in the plant as the most severe

symptoms occur on the older leaves (Viets et al., 1954). Heavy liming of

a soil may lower the availability of zinc; also, heavy phosphorus fertilization may reduce zinc absorption (Bingham and Martin, 1956). Treatments of 50 pounds Es-Min-El or 5 pounds of zinc sulfate corrected

zinc deficiency in soil from the Black Belt of Mississippi. In this

case, a vegetative response of soybeans (LEE) to zinc fertilization was

obtained, although severe chlorosis of the unfertilized plants did not

occur (Nelson, 1956).

Copper deficiency may cause severe stunting of growth, but moderate

deficiency may merely reduce yields. The rate of photosynthesis is low

in copper-deficient plants, and there is evidence that the element is

involved in oxidation-reduction reactions and as an enzyme activator

(Reuther, 1957). Response of soybeans to copper has been observed on

peat and muck soils in the Everglades (Allison et al., 1927) and in

Indiana ( S. R. Wilkinson, personal communication).

Aluminum, commonly present in the soil in large amounts, may be

essential to plants, though this is difficult to demonstrate, and it is not

likely that it will ever be deficient (Bear, 1957). Aluminum is toxic to

soybeans only in strongly acid soils, and proper liming to pH 6.0 will

ordinarily correct any toxicity (Kamprath, 1958).

Chloride content of the tops in a soybean variety (LEE), on plots

receiving variable amounts of KCl, was found to be low and essentially

constant, whereas, the chloride content of corn tissue varied with the



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