Relative Maturity and Population Effects on Yield Components in Double-Crop Soybean in Indiana.

A broad range of soybean plant stands often produce similar grain yield through compensating mechanisms such as branching, pod set, seed fill, and seed size. The relative maturity of soybean varieties has a direct impact on the physiological development and yield potential as well. To date, no research has been performed examining the yield components for double-crop soybean in Indiana. In 2016, cultivars varying in relative maturity (RM) [3.4, 3.8, and 4.6] were planted at five seed rates (123,000 to 613,000 seeds ha^-1) on June 21 after winter wheat harvest at the Southwest Purdue Ag Center near Vincennes. At maturity, plant stands of 100,000; 200,000; and 300,000 plants ha^-1 were sampled within each maturity group with three replications. Plants were hand-harvested from 0.41 m² for intensive mapping of yield components. Pods were counted based on nodal position within the canopy as well as main-stem vs. branch location. Trifoliate nodes and reproductive nodes were counted. Seed weight, grain and stover biomass, and thereby harvest index were also measured. Pods and grain mass plant^-1 were reduced at higher population, but grain mass m^-2 was consistent across population and RM. Population had an effect on pods plant^-1 while RM did not. Both population and RM did not have an effect on pods m^-2. These results demonstrate how soybean is physiologically able to compensate yield at various populations when growing conditions are favorable. This study will be repeated in 2017.