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

摘要

As 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 /.ones 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 determinedby 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.