Miranda Ochs

M.S. Level Student
University of Illinois Urbana-Champaign
Advised by Dr. Fred Below

Soybean Planting Date Impacts the Response to Agronomic Management

Traditionally in the US cornbelt, growers plant soybean [Glycine max (L.) Merr.] fields after maize (Zea mays L.) due to greater profitability potential. In recent years, there has been a paradigm shift in planting soybean first as there is potential for greater yields when compared to later-planted soybean. What remains to be determined is if a change in planting date necessitates a change in agronomic management to optimize the soybean yield, which is the objective of this study. Sixteen soybean varieties with varying relative maturity (RM) were planted across two row spacings (51 or 76 cm), two levels of preplant fertility (none or 67 kg P2O5 and 17 kg S ha-1), and two levels of foliar protection (none or fungicide with insecticide at the R3 growth stage) in a complete factorial design. Soybeans were planted on 23 April, 9 May, 31 May, and 15 June 2022. On average, the April-planted soybeans yielded the most at 4.44 Mg ha-1 with decreasing yield with later planting. Fertility and row spacing significantly affected grain yield only on soybean planting date 9 May, indicating overall low response to these management practices in the study. Foliar protection was the only management practice that consistently increased grain yield for all planting dates, resulting in yield increments ranging from 0.18 to 0.23 Mg ha-1. Therefore, early planting of soybean is a management practice that can significantly increase grain yield compared to normal or late planting dates, and other than using later RM varieties for the region and providing foliar protection it does not appear to require fertility and row spacing changes to optimize yield.