Research HighlightsBreeding Climate-Smart Soybeans Starts at the Roots
Highlights:
- As soybeans fix nitrogen, they also create high-nitrogen residues that feed soil microbes that may produce nitrous oxide, a greenhouse gas released from the soil as crops grow.
- Researchers are exploring if soybean varieties differ in greenhouse gas emissions allowed by the microbes around their roots.
- Their first step is characterizing differences in soybean roots and greenhouse gas emissions measurements by variety.
- Combining that data will identify potential soybean lines that can serve as parents for breeding soybean varieties with lower emissions potential.
By Laura Temple
Greenhouse gases in the atmosphere absorb heat coming from Earth’s surface. Natural biological processes release some of the most common greenhouse gases, like water vapor, carbon dioxide and nitrous oxide, or N2O. Efforts labeled “climate-smart” aim to reduce greenhouse gas emissions.
According to Bo Zhang, associate professor and soybean breeder at Virginia Tech, up to 80% of the N2O in the food supply chain comes from the soil.
“We observed variation in greenhouse gas emissions among soil samples collected from Virginia agricultural research stations in a 2024 pilot study,” she reports. “These findings led us to hypothesize that soybean varieties may influence soil emissions. Our current research has the long-term goal of developing soybean varieties that reduce greenhouse gas emissions from farmers’ fields.”
A national Soy Checkoff investment funds this basic research. Though U.S. soybeans already carry the lowest carbon footprint compared to soy of other origins, the future soybean varieties Zhang describes would support continuous improvement in the sustainability of U.S. Soy. Raising such varieties could add value and open up new market opportunities soy users focused on reaching specific sustainability goals, potentially increasing demand for U.S. Soy.
For this research, Zhang is partnering with Huijie Gan, Virginia Tech assistant professor for soil ecology, and Ryan Stewart, professor focused on quantifying interactions between water, soil and plants. Together, they are taking a unique approach to reducing greenhouse gas emissions from soybeans.
Digging into Root Structures
Soybeans use nitrogen to produce high protein levels that make them valuable for both food and feed.
“As soybeans fix nitrogen from the atmosphere in root nodules, they also provide high-nitrogen residues that feed soil microbes,” Gan explains. “Sometimes some nitrous oxide leaks into the environment during microbial processing of the nitrogen. That is the main contributor of emissions from the soil.”
Soil microbes interacting with soybean roots determine nitrogen fixation, plant-available nitrogen and byproduct created. This interaction may also connect to the amount of N2O released.
Gan notes that other soybean research established links between genetics and soil interactions in the roots. However, her review of existing research found a knowledge gap in understanding root traits.
“We started by establishing a platform to quantify root phenotypes,” she says.
She led an effort to compare, analyze and describe the observable differences of about 200 soybean genotypes. She grew the soybeans in a hydroponics system to view root development, using image analysis to characterize their roots.
“We selected a panel of nine genotypes with different root to shoot ratios for growth trials,” Gan says. “This will help us connect root genotypes to emissions.”
Measuring Emissions
The nine selected soybeans with different root characteristics are being grown in replicated trials in both the greenhouse and the field. As a soil physicist, Stewart is leading the effort to measure greenhouse gas emissions from these plants.
“We are measuring carbon dioxide and methane, but the nitrous oxide emissions are the most variable and of the greatest interest,” he says.
In the greenhouse, the team places plants in enclosed chambers to measure emissions over a specific time period. The controlled environment allows for accurate measurement and will help identify links between genotypes and emissions. However, in-field data provides the most complete perspective on what is happening.
“Emissions are harder to contain in the field, and environmental factors like temperature and moisture influence what is happening,” Stewart explains.
He combines a variety of measurements to understand what is happening around soybeans in field trials. Caps mounted on collars inserted in the soil capture gases leaving or entering those chambers around a plant for a short time. Physical soil samples quantify characteristics like soil moisture and the forms of nitrogen in the soil. The team also plans to dig up the plants to characterize root traits and microbes living near the roots.
They plan to conduct these field trials for two years, to account for more environmental variability and validate connections between root types and N2O emissions.
Linking Genetics to Emissions
Sequencing the nine soybean genotypes in the growth trials provides comprehensive genetic information. Zhang plans to compare those genetics with the phenotypic data gathered from root characterization and the greenhouse gas emissions data from the greenhouse and field trials.
“Together, that data will allow us to identify structural variations in the genome that may be linked to lower greenhouse gas emissions,” she says. “This will help us select potential parental lines, with breeding expected to start in the third year of this project.”
At that time, the team intends to conduct an economic analysis to determine how selecting varieties with lower greenhouse gas emissions could impact farmer return on investment.
Zhang acknowledges that once the breeding process starts, new varieties will still be years away. However, she believes that this research is laying a solid foundation to help U.S. soybean farmers continuously improve.
As sustainability and carbon footprint become requirements for more customers around the world, soybean varieties developed from the genetics that emerge from this work could add value across the U.S. Soy industry.
Additional Resources
Virginia Tech Soybean Breeding – website
Improving Roots Improves Soybean Yields – SRIN article
U.S. Soy Partners Update National Sustainability Continuous Improvement Goals – United Soybean Board article
Meet the Researcher: Bo Zhang SRIN profile | University profile
Published: Aug 25, 2025
The materials on SRIN were funded with checkoff dollars from United Soybean Board and the North Central Soybean Research Program. To find checkoff funded research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.
