Effect of Planting Date and Row Spacing on Performance of Soybeans in Eastern South Dakota.

Long-term, the climate change trends in South Dakota have resulted in a relatively longer growing season and an increase in precipitation.  The effects of these climate changes on soybean performance are unknown. Climate change trends and simple year-to-year variability in weather often push the limits of what is considered early and late planting dates and data from long-term planting date studies have been used to make revisions in crop insurance. Climate change also influences other management practices like row spacing. It is therefore important to initiate long-term studies to determine whether revisions to best management practices for soybean are needed. In 2014, two studies were conducted in South Dakota, the first a date of planting study, conducted at one location to assess the yield response curve.  The second study was a row spacing study conducted at three locations (Volga, Beresford, and Aberdeen). The planting date study had four planting dates that were two weeks apart, two seed treatments (with and without fungicide), two variety 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. The row spacing study contained two varieties (one resistant to white mold, the other susceptible) with maturity ratings specific to each location, two row spacing treatments (8 and 30-inch) and four seeding rates (100,000, 135,000, 170,000, and 205,000 live seeds/acre). In the planting date study, planting date, variety maturity rating, seed treatment, and seeding rates had statistically significant effects on soybean seed yield. For the row spacing study, in Aberdeen the 8-inch row spacing yielded the best with optimum yield at a seeding rate of 170,000 seeds/acre. In Beresford, the two row spacing treatments were equal in yield with both having optimum yield at a seeding rate of 170,000 seeds/ac.  These 2014 results as well as second season results will be presented in detail in the poster.