Soybean growth and yield response to interplant competition relief in various plant density environments

Soybeans have the ability to regulate growth and yield component production in response to changes in plant population and competition. Previous research has addressed these issues from various aspects, however, there is a lack of information regarding how interplant competition affects plant size variability, or how different sized plants respond to different plant density environments, or how plants respond to competition relief at various developmental stages. Research was conducted in Urbana, Illinois to examine yield component and growth variability by plant density, interplant competition, and cohort size. Two soybean cultivars (AG3803 and AG3205) were established at initial plant densities of 15, 30, 45 and 60 plants m-2. Large and small cohorts were selected visually at four growth stages (V3, V6, R2, and R4) to be relieved of competition (-) (i.e. thinned) to 5.3 plants m-2, while similar sized (large or small) cohorts remained in the level of competition of the initial seeding density all season. Plant height, growth stage, and number of nodes were recorded at each respective thinning time for, both, cohorts relieved of competition, and cohorts that remained in competition. At maturity, yield component (pod count, seed count, seed mass) data were collected and analyzed as differences between levels of competition. Plants recovered by increasing total seed yield plant-1 for all timings and initial population densities when densities were thinned (interplant competition reduced). Earlier thinning times increased plant-1 seed yield by increasing pods plant-1 while seed mass contributed to yield compensation at the last thinning time. These results improve the understanding of soybean crop communities, and the relationship between plant density and plant size variability