Updated October 29, 2020:
Soybean seed protein concentration has decreased over the years. Although new, high protein soybean varieties are in breeders’ pipelines, these varieties may not be widely available for some years. If a crop management strategy can be identified that increases seed protein, growers would have the immediate option to implement this strategy on their farms. The objectives of this study were to understand the impacts of various management factors on seed protein concentration and determine the role of nitrogen fixation in seed composition responses to management. This project will guide future management recommendations and studies, and it will identify physiological traits that are important for increasing seed protein concentration.

The project included a meta-analysis and field experiments. The meta-analysis combined data from 64 previously published experiments, and peer-reviewed articles performed a new statistical analysis to identify management factors that are very likely to improve seed protein concentration. Across studies, sulfur fertilizer application significantly increased both yield and seed protein concentration in soybean seeds. Nitrogen fertilizer application, tillage, plant density, and irrigation did not affect seed protein concentration. Weather affected the responsiveness of seed protein to management; higher growing season temperatures increased the seed protein responsiveness, as did higher growing season rainfall. The field experiments included multiple MG 5-7 genotypes, and these tests were conducted at multiple sites in North Carolina and South Carolina from 2018 to 2020. Data from 2019 are being analyzed, and data from 2020 will be available after harvest in November. When field studies are complete, the final results will be published in peer-reviewed journals and communicated to growers and extension agents.