Seeding RATE Implications for Single-ROW and Twin-ROW Soybean Production in the Mississippi DELTA.

Many aspects of soybean production have been evaluated over the last forty years with a major shift from planting in May and June to the Early Soybean Production System (ESPS) developed by Dr. Larry Heatherly with USDA-ARS. Grain yields have grown from less than 20 bu/acre to irrigated yields approaching 100 bu/acre with a state average over 50 bu/acre. In the same time frame, irrigation has become a common practice along with twin-row planting (TR, two rows on the same bed). An effort was afoot to shift to no-till without beds but that quickly was deemed unacceptable as beds are required to get water off the field (drainage) and on the field (irrigation). In an effort to decrease input cost while maintaining profitability, a multi-year project was funded through the Mississippi Soybean Promotion Board to study inputs. Many producers had been increasing seeding rates in an effort to increase yield yet that practice also increased costs. One series of studies evaluated seeding rate of 6, 8, 10, and 12 seed/ft (78,408, 104,544, 130,680, and 156,816 seed/acre) in either single-row (SR) or twin-row (TR) planting systems. An early vs late planting date was also included. After the first year, the seeding rate was further reduced since no yield loss was measured with the higher seeding rates. Grain yields were determined by harvesting the center two rows with a plot combine and retrieving a grad sample for determining harvest moisture, bushel test weight, and Seed Index (100-seed weight). Four plants were also removed to the lab to determine plant height, main stem nodes, main stem pods, branch nodes, and branch pods. Grain yields were not significantly reduced with 6 seeds/ft in either TR or SR. Branching greatly increased and branch pods greatly increased as main stems decreased (at lower seeding rates).