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Research Highlights
Exploring the Impact of Genetics on Soybean Test Weight

Photo: United Soybean Board

By Laura Temple

Soybeans should weigh 60 pounds per bushel, according to the U.S. standard recommended in 1925. If test weights fall below 54 pounds per bushel, the soybeans receive a lower quality grade, meaning farmers can be docked.

“Soybean test weights have been decreasing over time,” says Jenny Koebernick, soybean and cotton breeder and assistant professor for Auburn University. “Breeders want to add value to soybeans and help improve them. That’s led to asking questions about what traits contributing to test weight can be improved through breeding and are not environmental.”

Koebernick acknowledges that many environmental factors impact soybean weight. However, for years, direct breeding efforts have improved soybean yield. To learn if a similar approach could improve test weights, she focused breeding efforts on understanding soybean quality with a checkoff investment from Alabama Soybean Producers. Once the project was underway, she leveraged early efforts to participate in a multi-state study funded by an additional checkoff investment from the United Soybean Board.

“Test weight determines the bushels in a load for storage, crushing conditions, transportation needs and much more,” she explains. “Improving test weights would benefit the entire soybean supply chain, from farmers to end users.”

However, to improve traits, breeders need to thoroughly understand them. The work Koebernick has completed so far is gathering that type of information — with research specific to Alabama as well as contributions to the broader effort.

Exploring Genetics to Identify Molecular Markers

One trial, a genome-wide association study, includes a wide range of genetic material, all within Maturity Group 5. This trial is underway to determine which traits impact test weights the most. During the past two years, Koebernick and others around the country have grown and collected data on 300 lines with a wide variety of characteristics that could contribute to test weight, such as protein content, oil content, seed size and more.

The data should help Koebernick and other researchers identify genetic markers associated with DNA that could influence test weights, so they can easily find those traits in lines beyond this study.

Identifying Similarities Across Environments

As part of the multi-state study, she and her team evaluated a large number of soybean breeding lines from late Maturity Group 4 to Maturity Group 6. In addition to test weight, they recorded data on moisture content, seed size, seed quality and seed composition. The same lines were evaluated in other trials throughout the southern U.S.

“We know planting date impacts yield, so it could influence test weight,” Koebernick explains. “Conditions that delay soybean harvest past maturity may also impact weight.”

The trials in other locations included multiple planting and harvest dates.

“Seeing how these soybeans react in different environmental conditions will help us pinpoint what factors are heritable,” she says. “Compiling all the data from these lines, with known genetics, will help us learn what traits to look for that could influence test weights.”

Investigating Harvest Date Impact

At the same time, Koebernick chose to focus on how delayed harvest could influence soybean test weights in Alabama.

“Weather, including tropical storms, commonly delay soybean harvest for farmers,” she says. “We want to understand what is happening to soybean test weights and composition in mature soybeans sitting in the field.

Her team selected 25 soybean lines with great differences in composition and seed size from Maturity Groups 6 and 7, the two maturities grown in Alabama. The trials were harvested on time, then two weeks later and one month later.

“We are still evaluating this data, but it will help us learn more about how genetics and environmental factors work together to determine soybean weight,” Koebernick explains.

She values soybean checkoff support at both the state and national level. “Breeding projects like this focus on long-term deliverables,” she says. “We are very fortunate to have support for these projects. The Alabama Soybean Producers checkoff investment allowed us to start on these trials before the multi-state project was underway, giving us a head-start on tackling these questions.”

This project was funded by the soybean checkoff. To find research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.