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Research Highlights

Research Highlights
How Does Management Increase Soybean Seed Protein? A Mechanistic Approach to Identifying Limitations and Opportunities

Aerial images of experimental plots collected in Kentucky (top) and in Arkansas (middle and bottom) during the soybean growing season, which were sampled for various laboratory analyses related to nitrogen status. The bottom panel is the normalized difference vegetation index (NDVI) using near infrared (NIR); the NDVI has arbitrarily been assigned an orange color in this image.

By Montse Salmeron, University of Kentucky

Developing strategies that ensure U.S. soybean is competitive in global markets is essential for soybean producers. Annual U.S. soybean yields have increased by 0.49 bu/acre annually since 1986; seed protein concentration has fluctuated but declined slightly over the same period from about 35% in 1986 to about 34% in 2019, which could make it less competitive in the global marketplace. Seed composition (total protein and oil, amino acid and fatty acid profiles) is affected by genetic, environmental and management factors. Therefore, a combination of breeding efforts to address the genetic component and site-specific management practices are required for optimal productivity and quality of soybean seeds.

While numerous genetic solutions are being developed, the potential effects of management and cultural practices on seed composition has received relatively little attention. Soybean producers use a wide variety of management practices that can influence nitrogen availability (i.e., use of cover crops, fertilizer and inoculant applications). Combining phenotyping tools with process-based eco-physiological models provides new opportunities for site-specific recommendations. 

This $197,780 project specifically evaluated management practices that increase nitrogen availability during the seed-filling phase, quantifying changes after fallow vs. a winter cover crop, which affect the crop’s need for biological nitrogen fixation early in the season. Aerial images were also used to quantify crop nitrogen status. The dataset generated will help improve carbon- and nitrogen-cycling predictive tools in soybean.

Soybean field trials were conducted during 2019, and a second set of trials is planned for 2020. Preliminary results support the idea that management and cultural practices increase crop productivity through an indirect effect on nitrogen cycling. Growing irrigated soybean after a winter cereal rye cover crop increased soybean yields in two out of six cultivars in Kentucky and Arkansas. Additionally, late nitrogen fertilizer applications increased yields in Arkansas and Minnesota by as much as 5 bu/acre. Analysis of soybean seed composition is currently underway. 

This project will benefit U.S. soybean producers by providing information on how different management practices affect seed composition and yield, allowing them to make choices that could increase the value of the soybean meal they produce. The dataset generated by this project will be used by crop modelers to improve predictive tools for soybean carbon and nitrogen cycling, biological nitrogen fixation and seed composition. The evaluation of information collected from aerial images as diagnostic tools of nitrogen status will inform future research, allowing for site-specific recommendations. Given the negative correlation between soybean yield and seed protein concentration observed over the last decade, it has become imperative to identify management practices that will increase productivity of high-quality soybean crops without loss of yield, while ensuring long-term economic and environmental sustainability. 

To find research related to this Research Highlight, please visit the National Soybean Checkoff Research Database.