Research Highlights

Planting Green: Incorporating Cover Crops in Minnesota Soybeans

By Carol Brown

Most Midwest farmers have heard about the benefits of incorporating cover crops into their production system, but in some locales, it isn’t easy to do. In northern areas of the country, the shorter growing season makes the cash crop difficult to plant, harvest or both – even without the added complication of planting and terminating a cover crop.

University of Minnesota Extension Crop Educators Angie Peltier and Jodi DeJong-Hughes, UMN Extension Specialists Lindsay Pease and Anna Cates, members of the Minnesota Wheat On-Farm Research Network, crop advisors, and six farmers are fine-tuning the best ways to use cover crops in northwestern and west-central Minnesota. The project, “Planting Green Along the Red,” is supported by the Minnesota Soybean and Wheat Research and Promotion Councils. 

As the project name reflects, the researchers are focusing their study along Minnesota’s Red River Valley, starting in the north near Crookston and going south and east as far as Willmar. Their goals include finding the combination of cereal rye cover crop seeding rates and termination timing that provides the most benefits to the cash crops and the soil. The crop rotations included soybeans with wheat, corn silage and corn grain.

“I want to improve the amount of soil farmers keep in their fields,” Peltier says. “When the winds pick up, especially in a dry year, I’ve seen rolling, brownish clouds of soil in the atmosphere, which is not where soil is supposed to be. Adding a cover crop can help reduce soil loss from erosion by wind and water.”

In order to get the most from a rye cover crop, it needs to grow as long as possible. “Planting green” refers to a farmer planting their cash crop directly into a living cover crop, then terminating the cover crop afterward. This allows the cover crop’s surface biomass to accumulate, keeping the soil covered as long as possible, which can reduce soil erosion, improve soil organic matter and suppress weed growth. 

“We’ve designed a series of experiments with our farmer cooperators to hopefully make cover crops a bit more of an approachable conservation practice,” explains Peltier. “We want the farmer to remain profitable, but to also get the ecological services that cover crops can provide, combined with not tilling the land. The farmers are conducting production-scale strip trials on their own farms to help us find the best cover crop seeding rates and termination timing combination.”

The farmers’ experience levels with cover crops ranged from first-time users to a longtime cover cropper. The strip trials began in the fall of 2021 with the seeding of cereal rye. In the spring of 2022, they terminated the cover crop on separate strips of the field at three different time points: 7 to 10 days before the soybeans were planted, at planting, and 7 to 10 days after planting. 

The researchers and their teams are measuring the amount of rye biomass grown that season, as well as soybean plant height, stand count and yield. They are also monitoring weed growth and taking soil samples to measure bulk density, nutrients and moisture content. Peltier says these measurements can help paint the picture of the impact that cover crops can have on the cash crop.

The team is also conducting research with similar parameters on plots at Research and Outreach Centers near Crookston and Morris.

“At the research centers, we can find the nuances that are happening to better channel our recommendations to farmers,” says DeJong-Hughes, “and with the farmers’ field-scale tests, we can see how things work with their equipment and schedules.” 

For example, the researchers may have recommended a high cover crop seeding rate to the farmers based on their research plot findings. The good weather conditions they experienced allowed the cover crop to flourish in the spring. But by soybean harvest time, the remaining terminated cover crop biomass was still abundant.

“One of our farmer cooperators was harvesting soybeans in one plot where there wasn’t much rye biomass, so he could run the combine at 4.5 miles an hour,” says DeJong-Hughes. “In another plot, there was so much rye residue coming through the combine head that he had to slow down. Things like this can only be discovered on a field-scale rather than in a research plot.”

After harvest is complete, the research team will take soil samples again, and the farmers will submit their yield data as well. The researchers will then analyze this data over the winter to develop farmer recommendations by spring.

Because the team wanted to explore planting cash crops into living cover for several years and under different environmental conditions, they leveraged this checkoff project to earn a three-year Sustainable Agriculture Research and Education (SARE) grant, beginning November 2022. They will continue to explore planting green in the soybean–wheat, soybean–corn silage and soybean–corn grain rotations. 

“We are grateful for the Minnesota Soybean Research and Promotion Council for funding this first year of the trial,” says Peltier. “With this additional funding from SARE, we can expand this project even further.” 

Published: Jan 16, 2023