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Research Highlights

Research Highlights
Effect of Cultural Practices on Soybean Seed Quality: A Review and Research Studies

By Dan Davidson, Illinois Soybean Association

A team of researchers across the Midwest is exploring how today’s management practices influence oil, protein and amino acid composition in soybeans. The goal is to identify practices growers can adopt that will improve the compositional quality of the soybeans they sell, and to share that information with farmers. This project was funded for $431,344 in 2019. It is in the second year of a three-year program.

Soybean is the second-most-popular crop grown in the U.S. (after corn), with over 80 million acres planted annually. Producers grow and market soybeans as a commodity, delivering directly to elevators or crushers. The soybean oil and protein serve as feedstock for a range of items including both animal and human protein products, edible and industrial oils, and other commercial products. Unfortunately, crude protein levels in U.S. soybean crops have declined below the 36% standard in recent years, as yields have increased while oil content has remained relatively stable.

Management practices are known to affect soybean yield. When growers adopt the best practices, and when weather cooperates, they can sometimes break the 100-bushel-per-acre ceiling on yield. However, it is not well-understood how these improved practices impact the protein and amino acid composition in soybean seed. For comparison, in bread wheat, it is well-known that timely applications of nitrogen and sulfur can improve seed protein content. For protein levels and amino acid content in soybean, it has long been known that both weather and genetics play a role, but how management practices impact these two components has not been well-established.

This project has three main goals: to use data from past field studies to evaluate the impact of cultural practices on protein content; to conduct field studies to identify best management practices that improve protein and essential amino acids; and to conduct a survey to assess grower knowledge and attitudes about seed quality and what practices could impact soybean seed composition at harvest.

A meta-analysis of previously collected data was undertaken to study and identify management practices that could affect composition. The goal was to identify practices that growers could adopt to sustain the recent gains in soybean yield, while at the same time improving or maintaining high levels of protein in the harvested seed. In U.S. soybean crops, it is known that protein levels can vary with geography. However, changes in amino acid composition across locations had not previously been studied. By analyzing the results of studies conducted across 14 states from 2012 to 2016, a trend was identified, with greater amino acid concentrations in southern than in northern latitudes. This work was published and shared widely with growers through extension activities.

Spatial variation of essential amino acids cysteine and methionine (two of the amino acids that make up protein) in U.S. soybeans.

The investigation also focused on determining how management practices influence protein levels. While environment remains the dominant factor determining protein concentrations from year to year, management practices do have an impact. Some of the findings are listed below.

  • Diverse crop rotations can improve protein levels.
  • Application of small amounts of nitrogen (< 50 lb./acre) improved both seed protein content and amino acid composition.
  • No effects on protein concentration were evident from today’s most popular practices, including no-till, early planting, lower populations and narrower rows, seed treatment, foliar protection and foliar feeding.
  • Maturity group (MG) selection did not influence amino acid composition in the northern states, but it did in the southern states, with longer MGs showing a decline in oil and an increase in protein.

One of the strategies that many growers practice is treating soybean seed with a rhizobia inoculant to improve nodulation and nitrogen fixation and yield, which might be expected to improve protein and amino acid quality. A comparison was made between no inoculation, seed inoculation, seed and soil inoculation at V4, and seed and soil inoculation at R1, and no effect was found under any conditions. The conclusion was that in fields where soybeans were previously grown, and under ideal conditions with no stress, there was no benefit from inoculation or co-inoculation on seed quality.

Data analysis continues, and new results will be published and reported as they are obtained.

Improving the protein content and oil quality has long been a mission of the soybean checkoff, in order to increase the value of U.S. soybeans in a competitive market. Growers can currently buy varieties that have greater protein levels, and soon they may be able to choose better management practices that can further improve the quality of their seed products.

“We still have a lot to learn about improving quality, but this is a great first step,” said Dr. Ignacio Ciampitti, farming systems professor in the department of agronomy at Kansas State University and principal investigator on this project. “Quality is the result of multiple factors. We need more knowledge to understand the complexity involved in choosing both the right variety and selecting and selecting the right management practices to optimize protein under current environmental conditions.”

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