Partitioning Soybean Seed Yield Components1

Abstract

Little is known about the nodal distribution of seed yield components in short‐seasoned soybeans [Glycine max (L.) Merr.]. This study was initiated to determine the effect of row width and plant density on the seed yield and yield components at each node of ‘Evans,’ a group O soybean cultivar. Field trials were planted in late May 1979 and 1980. The 25, 50 and (in 1980 only) 75 cm row widths were factorially arranged with plant densities of 25, 80 and 135 seeds/m2 in a fine sandy loam (Typic Udifluvents). Seed yield increased by 31% and 12 to 16% when row width was decreased from 75 and 50 cm, respectively, to 25 cm. Seed yield increased 13 to 27% when plant density was increased from the low to the medium density. Medium and high densities had similar seed yields. Final seed yields averaged 4,110 kg/ha in 1979 and 4,950 kg/ha in 1980. The number of pods per plant and per node was the yield component most affected by increasing row width or plant density. Pod number per plant increased as row width was narrowed and decreased with increasing plant density. The number of seeds per pod and seed size showed minor changes in response to changes in row width, plant density, and node position on the plant. Nodes 5 to 9 had the greatest percentage of seed yield (36 to 67%) compared to nodes 1 to 4, 10 to 14, and 15 to 20, in all treatments except forplants in the low density, 25 cm row spacing plot where branches contributed most of the yield at the lowest main axis nodes. Branches in low densities produced 30 to 40% of the seed yield in both years, while in the medium and high densities branches contributed 5 to 16% of seed yield.