Soybean Seed Treatments Consistently Increase Plant Populations but Inconsistently Yield and Partial Returns.

Soybean {Glycine max (L.) Merr.} is now a high-value crop so growers manage the crop more intensively, including using the myriad new seed treatment options. Field-scale studies were conducted at four locations in New York in 2012 and 2013 to determine if rhizobia (Bradyrhizobium japonicum), biological, fungicide, and insecticide seed treatment combinations increase yield and partial return. Location by seed treatment interactions were observed for early plant populations, yield, and partial return. When averaged across years, rhizobia/biological/fungicide seed treatment vs. untreated seed increased early plant populations by 22% and 8% but not yield at two locations. Rhizobia/biological/fungicide/insecticide seed treatment vs. untreated seed increased early plant populations (20% and 10%) and yield (7% and 4.5%) at two other locations, and partial return ($155 ha^-1) where yield increased by 7%. Rhizobia/biological/ fungicide/insecticide seed treatment did not increase partial return where yield increased by 4.5% because increased partial costs (~$45 ha^-1) offset increased revenue. Early plant populations exceeded 30 plants m^-2 at all locations, which probably limited yield and partial return responses to seed treatments because soybean yields usually plateau when early plant populations exceed 25 plants m^-2. Growers who adopt seed treatment combinations could probably reduce their typical seeding rates by ~15%, which would increase the probability of increased partial returns. The application of rhizobia inoculant at planting vs. untreated seed did not increase yield and partial return, including two locations where soybean had been grown twice in the previous 10 years. Growers should reconsider this practice in fields with soybean history.