Short-season soybean yield compensation in response to population and water regime

Short-season soybean [Glycine max (L) Merr.] production systems, such as do uble cropping and late sowing, require high populations to optimize yield, but effects of high populations on seed number and seed mass are unknown. W e evaluated plant population effects on yield compensation, stability of ha rvest index, assimilate partitioning for seed number, and seed-filling char acteristics for 2 yr near Keiser, AR. The study had two cultivars, two leve ls of irrigation, and three row spacings that each had five levels of popul ation ranging from 6 to 134 plants m(-2). Increasing population reduced yie ld per plant but increased yield per unit area. Harvest index was relativel y constant across populations for a given year and irrigation regime, and y ield was closely associated dth biomass at maturity. At high populations, p lants maintained individual seed mass by reducing the proportion of shell m ass per pod. Final individual seed mass, seed growth rate (SGR), and the le ngth of effective filling period did not change with increasing population for irrigated or nonirrigated treatments. Reductions in yield caused by low population density were due to low seed number. Seed number per square met er,vas directly proportional to the ratio of crop growth rate (CGR) to SGR. For short-season production, high populations ensured early canopy coverag e and maximized light interception, CGR, and crop biomass, resulting in inc reased seed number and yield potential.