Genetic Gain X Management Interactions In Soybean: II Population Effects.

Plant breeders have increased genetic yield potential of soybean during the past century. The plant characteristics which soybean breeders have selected that have contributed most to those yield gains are largely not understood. One hypothesis is plants from recently released cultivars can withstand increased plant population (inter-plant competition) more effectively than earlier released cultivars and the objective of this study was to test this hypothesis. Soybean cultivars released over the last 80 years were evaluated at high and low seeding rates in research trials conducted in Illinois, Indiana, Minnesota and Wisconsin. In Illinois and Indiana, 57 maturity group III cultivars released between 1923 and 2007 were compared, and in Minnesota and Wisconsin, 59 maturity group II cultivars released between 1928 and 2008 were compared by seeding at high (445,000 seeds ha-1 ) and low (148,000 seeds ha-1 ) rates. Weekly digital images were taken and analyzed using SigmaScan to determine green canopy. At R8, 1 meter of row was harvested from each plot and branches were separated from stems. Heights, node count, pod count, biomass weight, seed count and seed weight were measured for stems. Pod count, biomass weight, seed count and seed weight were measured for branches. At maturity, seed yield, moisture, seed mass and grain composition data were measured and analyzed. Final plant stands averaged 311,000 and 94,000 plants ha-1 for the high and low seeding rates, respectively. Seed yield was -706 to 1456 kg ha-1 higher for the high seeding rate versus low seeding rate throughout all cultivar release years.