Soybean seeding rate and seed treatment that maximize yield and profitability based on planting date

Warmer spring temperatures and a growing body of literature on the importance of timely planting have resulted in many growers in Michigan and other northern U.S. states planting soybean [Glycine max (L.) Merr.]. However, there is limited research in Michigan informing how other management practices should be adjusted based on planting date (PD). Field experiments were conducted at two locations in Michigan using a split-plot design during the 2018 and 2019 growing seasons to determine how seeding rate (SR; 124,000 to 519,000 seeds ha(-1)) and seed treatment (ST; fungicide + insecticide + nematicide) impact soybean yield and net returns based on PD. Soybean was planted at five SRs with or without an ST (split-plot) on four PDs (main-plot). The use of the ST increased plant stand by 6.7% at one location but did not improve yield at either location regardless of PD. The increased cost associated with the ST and lack of a yield increase resulted in a US$25 ha(-1) decrease in net returns. Maximum yield was achieved with a final plant stand of 242,000, 288,000, 307,000, and 384,000 plants ha(-1) during the late April, mid-May, early June, and late June PDs, respectively. However, the final population to achieve maximum net returns ranged from 89,000 to 141,000 plants ha(-1) less than the population that maximized seed yield. Overall, results indicated that ST did not improve net returns across any PD, and relatively lower SRs were able to achieve maximum yield and net returns during early season planting, but increased SRs were necessary when planting was delayed.