Seed yield, seed quality, profitability, and risk analysis among double crop soybean maturity groups and seeding rates

Double crop soybean [Glycine max (L.) Merr.] production is common after soft red winter wheat (Triticum aestivum L.) harvest in the Upper Mid-South and Ohio River Valley regions. However, optimal maturity group and seeding rate information is needed because most double crop soybean research is at least 45-yr old. Relative maturity groups (rMG) 2.8, 3.5, 4.1, and 4.7, which ranged from a very short to an adapted long maturity group for the area, were evaluated at five seeding rates (123,600, 247,100, 370,700, 494,200, and 617,800 seeds ha⁻¹) in a double crop soybean study at Princeton KY, from 2017 to 2019. The longest rMG (4.7) had the greatest seed yield and seeds m⁻². However, rMG did not influence V2 and R8 plant population. The highest seeding rates of 494,200 and 617,800 seeds ha⁻¹ had the greatest yield and seeds m⁻² as well as the greatest V2 and R8 plant populations. Seeding rate did not affect protein or oil concentrations. Partial budget analysis determined that the combinations of rMG 4.1 at 494,200 seeds ha⁻¹, rMG 4.7 at 494,200 seeds ha⁻¹, and rMG 4.7 at 617,800 seeds ha⁻¹ had similar economic net benefits as the University of Kentucky recommendation of rMG 4.7 at 370,000 seeds ha⁻¹. However, the risk analysis predicted that rMG 4.7 at 494,200 seeds ha⁻¹ would have the highest probability of a positive net return. These findings support the use of a longer rMG for the region as well as an increased seeding rate to maximize yield and economic net benefit.