Genetic gain X management interaction in soybean: seeding rate effect

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 not well understood. The hypothesis states that 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 is 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. Seed yield was higher for the high seeding rate versus low seeding rate throughout all cultivars and years of release, but a larger difference was observed between seeding rates in newer cultivars. The yield increase came from an increased number of pods and seeds plant¯¹, and improved harvest index for both seeding rates. Although the high seeding rate provided higher yields, the low seeding rate had a larger increase in yield plant¯¹. This increase was due to newer cultivars having a greater branching ability at the low seeding rate while branching slightly decreased at the high seeding rate. I conclude newer cultivars are better able to compensate yield than older cultivars by producing more seed on branches under lower plant populations