No abstract

Soybean [Glycine max (L.) Merr.] is used extensively to meet the protein needs of animals and humans. Although a good source of protein, soybean's nutritional value is limited by low concentrations of sulfur‐containing amino acids (i.e., methionine and cysteine). Thus, it is often necessary to supplement diets with synthetic amino acids, a practice that can be expensive and adds complexity to the diet formulation process. The objective of this study was to determine if amino acid concentrations in recent high protein germplasm releases differ from those in normal protein cultivars. The high protein (HP) lines BARC‐6, BARC‐7, BARC‐8, and BARC‐9 and a normal protein check, either Essex or Manokin were grown in eight different environments from 1989 to 1991. Seed was analyzed for amino acid concentrations, protein, oil, crude fiber, ash, carbohydrate, and moisture. Protein concentration of HP lines ranged from 495 to 530 g kg−1. The HP lines were lower in oil, crude fiber, and carbohydrate compared to the checks. Concentrations of 14 of the 17 amino acids differed among entries. Concentration of cysteine of BARC‐8, 13.7 g kg−1, was higher than any other entry. Methionine concentration of BARC‐7 (10.8 g kg−1) and lysine concentration of BARC‐9 (55.0 g kg−1) were significantly lower than the checks. Feeding trials are necessary to determine the practical significance of these amino acid differences.

No abstract

Synopsis Three methods of statistical analysis were similar in detecting lines exhibiting unexpected performance in the F1 generation, but gave different estimates on which were based the interpretations of parental‐F1 relationships.

Nitrogen metabolism differences, including N2 fixation, between high‐and normal‐seed‐protein soybean [Glycine max (L.) Merr.] lines of equivalent plant maturity and seed yielding ability have not been determined in field tests. A replicated field experiment was conducted in 1985 and 1986 to determine such differences on a Mattapex silt loam (fine, silty, mixed, mesic Aqualfic Hapludult) with low soil N. The study used the nodulating‐nonnodulating N difference method to estimate N2 fixation of two soybean lines with contrasting seed protein levels. Eight sequential harvests were conducted from R5 (beginning seed) to combine harvest for the dry weights and N contents of vegetative and reproductive portions of the plants. There was no significant difference between the 2‐yr mean seed yields of the high‐ and normal‐protein lines, but the high‐protein line was 2 d later in maturity. The high‐protein line accumulated more N, fixed more N2, and remobilized more N to the seed than did the normal‐protein line (231 vs. 194, 114 vs. 77, and 87 vs. 76 kg ha−1, respectively). The greater N accumulation by the high‐protein line resulted from N2 fixation being sustained until the late R6 (full seed) stage. Nodule occupancy by strains of Bradyrhizobium japonicum was similar for the high‐ and normal‐seed‐protein lines. Thus, the ability to sustain N2 fixation until later stages of reproduction is a host plant attribute that may contribute to the greater N metabolism of a high‐seed‐protein soybean.