Yield and Composition of Soybean Seed as Affected by N and S Fertilization¹

Abstract

Soybeans (Glycine max (L.) Merr.) obtain nitrogen from soil and from symbiotic fixation when nodulated with effective strains of rhizobia. These two sources of N may need to be supplemented with fertilizer N for maximum seed yields. The objectives of the present study were to determine the effects of N and sulfur fertilization on soybean seed yield and other seed properties (protein, oil, amino acid, fatty acid, and S composition). Chippewa 64 and a nodulating‐nonnodulating (nodnonnod) pair of isolines of Chippewa background were examined at three field locations over 2 years for yield response to different forms of fertilizer N (224 kg/ha) and to fertilizer S (224 kg/ha). Three readily available fertilizers (ammonium nitrate, urea, and urea + sulfur) and two slow release fertilizer (S‐coated urea and ureaformaldehyde) were mixed in the top 20 cm of soil before planting. The soils were Nicollet silty clay loam (Aquic Hapludoll), McIntosh silt loam (Aeric Calciaquoll) and Webster clay loam (Typic Haplaquoll). Response to N fertilizer was greater with the nonnod isoline than with the other two lines. Nitrogen fertilization increased seed yield, weight per seed, seed protein percentage, and kg protein/ha. Plant height and lodging were either increased or unaffected, depending upon locations and/or year. Seed oil percentage decreased following N fertilization. However, total oil production usually increased due to larger yields. All sources of fertilizer decreased N2 fixation, plant nodule weight, nodule number, and weight per nodule. Amino acids increased uniformly with protein increases but fatty acid composition was unchanged. Sulfur fertilizer increased seed yield in one case and decreased seed yield in two cases depending on location and year. Total S percentage of the seed and S‐containing amino acids of the seed were not increased with S additions. Increases in seed yield and/or seed protein percentage in the nodulating lines suggest N2 fixation failed to supply amounts of N essential for maximum seed yield and/or protein percentage. With the recent concern for energy, N2 fixation must be increased to provide the N needed for maximum seed yields of soybeans rather than relying on fertilizer N.

Nitrogen Sources and Rates Affect Soybean Seed Composition in Mississippi

“…Previous studies have shown that protein and oil concentrations were negatively correlated resulting in the opposite trend for soybean seed protein and oil concentration in response to N applications in our study on clay soil [16]. In agreement with our results, multiple studies have also reported inconsistent responses of soybean seed protein and oil content to N applications [10,15,16,[39][40][41][42]. In Arkansas, 112 kg N ha −1 when applied at the R2 growth stage in soybeans caused no changes in seed protein and oil concentration compared to unfertilized soybeans on silt loam soil [40].…”

“…No changes in fatty acids content due to N applications was observed by Ham et al (1975) and Bennett and Krishnan (2005) [35,39]. Ham et al (1975) found that fatty acids including palmitic acid, stearic acid, oleic acid, linoleic acid and linolenic acid did not change with pre-plant N application at 224 kg ha −1 in Minnesota [39].…”

Influence of tillage system and starting N fertilization on seed yield and quality of soybean Glycine max (L.) Merrill

“…also Baker and Sawyer (2005) stated that n application before sowing or at early growth stages could suppress the process of n fixation. Similarly, Ham et al (1975) claimed that no matter what kind of nitrogen fertilizer is used, fertilization decreased n fixation by plants, a number of the nodules and their weight per plant. as a matter of fact, soybean is totally dependent on soil n from the stage of emergence to the stage of two true leaves and this time is the so-called hunger period.…”

Distribution and Mobilization of Sulfur during Soybean Reproduction

“…Three other studies on North American soils (Ham et aL, 1975;Brown et aL, 1981; and Sweeney and Grande, 1993), found soil sulfur fertilization to have no, or a variable, effect on soybean seed yield.…”