Growing solutions — how scientists and farmers are teaming up to revive soil health

BY LOUISA SMITH, AGRICULTURAL COMMUNICATION & MARKETING, BS '25

What do legumes, high tunnels, and scientists have in common? They are all key parts of a new University of Minnesota project.

Scientists are partnering 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 known as specific plants that are grown in the off season to enhance soil quality. In this experiment they are being focused on 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,” said Julie Grossman, associate dean of undergraduate programs, horticulture professor, and soil scientist at the U of M’s College of Food, Agricultural and Natural Resource Sciences (CFANS).  “We're trying to find ways to alleviate those negative pressures, and even enhance soil quality on the soil by using cover crops.”

Starting strong 

The project  started with a $1.5 million grant from the USDA and a presentation at the Marbleseed Organic Farming Conference. 

On the day of the conference, Grossman hoped to gauge the interest of farmers in high tunnel cover cropping, the theme of the workshop. 

“There was a huge snowstorm the night before, and my workshop was at 8 a.m.; I thought nobody would come,” Grossman said. “When I arrived the room was packed!”

The result of a live survey during the talk showed the number one barrier to using cover crops was lack of understanding, not lack of interest.

After the conference, they spread the word in organic farming newsletters, with more than 100 farmers showing interest. Ultimately 40 farmers received and tested the seed.

Cover cropping

Participating  farmers are sent legume cover crop seed samples to try in their high tunnel systems. Legumes, such as peas and beans, are nitrogen-fixing plants, taking nitrogen from the air and trapping it in their leaves with the help of a 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 go to the farm, take samples and analyze differences in their size and quality.

An interdisciplinary approach

Alongside the University of Minnesota, scientists from the University of New Hampshire are also working 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 said.

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 UMN 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 CFANS, is working alongside Minnesota vegetable growers to better understand how cover crops used in 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. The goal is to share practical insights through a series of real world case studies that can help other farmers decide if cover crops are a smart investment for their own operations. 

Building relationships

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. Farmers are also encouraged to use the universities as resources and ask questions along the way.

“Through that process we learn if there's a common problem that the farmers are having, or a challenge they’re facing,” Grossman said. “As a farmer-focused research team, my lab tries to always be responsive to farmers and develop our projects from a very applied perspective. We develop our research projects  to respond to farmer’s questions, so that we take on the risk of trying something new, and not the farmers.”

Environmental implications 

When using high tunnels, farmers replace the plastic covering every few years. This lets the soil sit for a span of months, and with exposure to rain, soil that was previously covered 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.

Looking forward 

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 said. “We want the project to be owned by the farmers, and for them to be able to make management decisions that fit their farm. We are planting the cover crops on working farms, each with differing rotations and crops, and growing the cover crops for different amounts of time — so it's reality. 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.”