Planting method and seeding rate effect on whole and partitioned soybean yield

Soybean [Glycine max (L.) Merr.] seeding rate is one of the most important management decisions. Although seeding rate effect on yield is one of the most examined management practices, its interactive effect with seeding method is often ignored. Two field trials were conducted in Arlington, WI, between 2019 and 2020. In the first trial, the interactive effect of seeding rate with seeding method (precision vs. random) and two cultivars was examined. Precision method used a vacuum seed meter and soybean seed plate, whereas the random method used a cone seed distribution system. The second trial was hand planted to mimic precision planting (exact seeding rates and within row spacings), and the effect of seeding rate on total and partitioned (branch and stem) soybean yield was assessed. The effect of seeding rate on yield varied due to seeding method and cultivar. Precision seeding increased yield for the lowest seeding rate (99,000 seeds ha(-1)) and was associated with increased canopy closure and more uniform within-row plant-to-plant spacing compared with the random seeding method. When soybean was hand planted (precision planting), total yield was greater only in the highest seeding rate. In the lowest rates, branch- and stem-derived yields were similar. Overall results show that precision planting can mitigate yield loss at suboptimal seeding rates. Results from these studies reveal the complexity of seeding rate optimization for maximizing soybean yield and resulting profit and highlight the need for farm-specific economic analysis for different management-related costs and soybean price scenarios.