Planting Date Effects on Soybean Performance in Eastern South Dakota.

South Dakota temperatures and spring rainfall have increased over the last several decades. These changes may affect how soybean planting dates, maturities, and plant seeding rates affect yield and grain quality. The objective of this study was to determine the optimal yield of soybeans as planting dates were delayed. In 2014 and 2015, a planting date study was conducted in Volga, South Dakota. The study had four planting dates; in 2014 they were: May 16^th, May 30^th, June 13^th, and June 27^th and in 2015 they were: May 4^th, May 20^th, June 2^nd, June 16^th. Also the study had two seed treatments (with and without fungicide), two maturities (1.4 and 2.4), and four seeding rates (100,000, 135,000, 170,000, and 205,000 live seeds/acre) using 30 inch row spacing. Planting date, variety maturity rating, seed treatment, and seeding rates influenced soybean yields in both years. In 2014, the yield decline with delayed planting was exponential due to an early frost, whereas soybean yield loss with delayed planting were linear in 2015. Increasing seeding rate had a positive effect on yield in both years but the yield increase was small, and was not economical. Seed fungicide treatment increased yields when soybeans were planted on May 30^th in 2014 and when they were planted on May 4^th and June 16^th in 2015 but was only economical for the May 4^th2015 planting date. Seed treatment did not influence protein or oil content in both years.