Teaming up to revive soil health

University of Minnesota Twin Cities scientists and partners are working with 40 organic vegetable producers to implement cover crops in their high tunnel systems and improve soil health for long-term productivity.

High tunnels are covered structures used by farmers to extend farming seasons. Cover crops are plants that are grown in the off-season to enhance soil quality, and in this experiment, they are being chosen for their nitrogen-fixing qualities.

“Because there are more crops being planted for longer periods of time [in high tunnels], the soils can degrade more rapidly,” says Julie Grossman, associate dean of undergraduate programs, horticulture professor, and soil scientist at the University of Minnesota’s College of Food, Agricultural and Natural Resource Sciences. “We're trying to find ways to alleviate those negative pressures, and even enhance soil quality … by using cover crops.”

Cover cropping

Participating farmers are sent cover crop seeds for legumes like peas and beans to try in their high tunnel systems. Legumes are nitrogen-fixing plants, taking nitrogen from the air and trapping it in their leaves with the help of soil-dwelling bacteria. When those cover crops are harvested at the end of the season, that nitrogen then returns to the soil. 

Traditionally, manure has been used as an organic fertilizer in high tunnels, but it can result in overapplication of phosphorus in the soil. Legumes can provide needed nitrogen without the excess phosphorus, resulting in a more balanced system.

Once the plants are growing, researchers take samples from the farm and analyze differences in their size and quality.

An interdisciplinary approach

Alongside the University of Minnesota Twin Cities, scientists from the University of New Hampshire are partnering on this project with participating farmers in their respective regions. University of Minnesota Research and Outreach Centers are also involved.

“We have the on-farm trials that each include one to two different cover crop legume species, but we also have a great collaboration with the North Central Research and Outreach Center in Grand Rapids where we have planted a research trial including all of the different species of cover crops being trialed by farmers at one site,” Grossman says.

An integral aspect of the project is the relationship building between universities and farmers. Throughout the process, farmers are surveyed to assess barriers and challenges they may be facing. They are encouraged to ask questions of the universities along the way.

The project has evolved into an interdisciplinary effort, including not just farmers and scientists, 
but also economists and educators.

On the educational side, the project partners with Renewing the Countryside, a Minnesota nonprofit that is working in partnership with University of Minnesota Extension to teach student farmers how to successfully grow crops in high tunnels. 

Gigi DiGiacomo, a research fellow in the Department of Applied Economics at the College of Food, Agricultural and Natural Resource Sciences, is working alongside Minnesota vegetable growers to better understand how cover crops from high tunnels affect the bottom line. By following growers over two seasons, her research will look at both the costs and potential benefits or savings from planting cover crops. 

Environmental implications 

When using high tunnels, farmers replace the plastic covering every few years. This lets the soil sit uncovered, and with exposure to rain, that soil now contributes to runoff.

“Imagine after years of manure application you have soil full of phosphorus, covered by high tunnel plastic,” Grossman said. “When the plastic is removed and it rains, there is a high potential for soil runoff and loss, taking the phosphorus with it and potentially ending up in our water bodies. That's the environmental challenge we're facing.”

When excess phosphorus moves into waterways, eutrophication (the enrichment of a body of water with nutrients, particularly phosphorus and nitrogen, leading to algae blooms) can occur.

“By using cover crops instead of manure, you're keeping excess phosphorus out of the soil, because the cover crop legume is providing nitrogen without the phosphorus,” Grossman said.

The project is new, but success has been found in early trials.

“Not surprisingly, we're finding a lot of variability and growth across the farms, and some outstanding cover crop production,” Grossman says. “We want the project to be owned by the farmers, and for them to be able to make management decisions that fit their farm. … At the end of the day, we're going to have critical information about what works, and how cover crops can be used to promote, and even restore, soil health in intensive high tunnel systems.”