Effects of Seed Size on Soybean Performance

Abstract A positive relation has been reported between size of seed planted and subsequent seed yield for several crop spcies, but limited research has produced inadequate information on this relationship in soybeans [Glycine max (L.) Merr.]. The potential for increased yield justifies further studies, especially in view of the relative ease of grading soybean seed for size. Use of more uniform seed also should result in greater uniformity of seed distribution by mechanical planters. Ten field experiments in 6 years compared effects of seed size on subsequent seed yield and certain plant characteristics that might be associated with yield of soybeans. Three or four seed size variables and three to eight genotypes were included in each experiment. Seed size variables were: (i) “large” — largest seed screened from each seed lot planted, (ii) “small” — smallest from each lot, (iii) “large‐small” — equal numbers of two sizes, and (iv) “field‐run” — un‐graded seed before removing large and small. Seed size had little or no effect on initial plant stand, plant mortality, lodging, and mean size of harvested seed. Genotype and year had pronounced effects upon percentage of barren plants, but no meaningful relationship was established between percentage of barren plants and seed yield. Average seed yield of progeny from large seed planted alone exceeded the yield from small seed by 5.4% in 10 experiments, from large‐small by 4.7% in eight experiments, and from field run by 3.3% in four experiments. Average seed yield from small seed equalled the yield from large‐small in eight experiments and was 3.2% less than from field run in four experiments. When large and small seed were planted in the same row, progeny from large seed always produced more yield than those from small seed. No genotype ✕ seed size interaction effects on yield were obtained. Seed size effects on progeny performance apparently were a response to relative seed size within a population and not a response to seed size per se.