Short‐Season Soybean Yield Compensation in Response to Population and Water Regime

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Abstract
Short‐season soybean [Glycine max (L) Merr.] production systems, such as double cropping and late sowing, require high populations to optimize yield, but effects of high populations on seed number and seed mass are unknown. We evaluated plant population effects on yield compensation, stability of harvest index, assimilate partitioning for seed number, and seed‐filling characteristics for 2 yr near Keiser, AR. The study had two cultivars, two levels of irrigation, and three row spacings that each had five levels of population ranging from 6 to 134 plants m−2 Increasing population reduced yield per plant but increased yield per unit area. Harvest index was relatively constant across populations for a given year and irrigation regime, and yield was closely associated with biomass at maturity. At high populations, plants maintained individual seed mass by reducing the proportion of shell mass per pod. Final individual seed mass, seed growth rate (SGR), and the length 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 meter was directly proportional to the ratio of crop growth rate (CGR) to SGR. For short‐season production, high populations ensured early canopy coverage and maximized light interception, CGR, and crop biomass, resulting in increased seed number and yield potential.