Comparison of variable‐rate prescriptions and optimum seeding rate in soybean

Abstract

AbstractAs the cost of soybean [Glycine max (L.) Merr.] seed increases, farmers are interested in reducing seeding rates. Variable‐rate seeding (VRS) allows farmers to adjust seeding rates within a field by management zone, and many farmers practice VRS in soybean. However, without field validation, the accuracy of existing VRS practices is unknown. The objectives of this study were to: (a) determine the agronomic optimum seeding rate (AOSR) of soybean in predetermined management zones and (b) compare the AOSR to each farmer's standard VRS practice. Ten on‐farm trials were established in Ohio and Michigan during 2017 and 2018. The trials consisted of three uniform seeding rate treatments of low, moderate, and high and a variable‐rate treatment determined by each cooperating farmer. Farmers used a variety of methods to create management zones within their fields. Within each site‐year, soybean grain yield was not different among management zones. The farmer‐selected seeding rate was within 10% of the calculated AOSR in 6 out of 15 management zones. In 8 out of 15 management zones, soybean was underseeded by >10%, and one management zone out of 15 was overseeded by >10%. Underseeding was likely due to low plant populations caused by heavy rainfall after planting or late planting, even though seeding rate was high. We recommend farmers take a stand count to understand the relationship between seeding rate and plant population in their individual field management zones and adjust their seeding rates accordingly.