By Scout Nelson
Scientists at the University of Minnesota Twin Cities, along with farmers and partners, are studying the benefits of planting cover crops in high tunnel systems. High tunnels are plastic-covered structures that help farmers extend their growing season, but because crops are planted for longer periods, soil can degrade more quickly. To address this, researchers are introducing cover crops like peas and beans, which are known for their nitrogen-fixing qualities.
Nitrogen-fixing legumes work with soil bacteria to capture nitrogen from the air and return it to the soil when the plants are harvested. This offers an alternative to manure, which has long been used as fertilizer in high tunnels but can lead to too much phosphorus buildup. Excess phosphorus in soil increases the risk of runoff, which can pollute waterways and cause harmful algae blooms
The project is being carried out with 40 organic vegetable producers across different regions. Seeds are provided to farmers, and researchers collect soil and plant samples to measure growth and quality. Trials are also being run at University Research and Outreach Centers for wider comparison. According to Professor Julie Grossman, the goal is not just scientific data but also strong collaboration with farmers, allowing them to make management decisions best suited for their operations.
The effort is interdisciplinary, involving scientists, economists, educators, and nonprofit organizations. Alongside soil research, economists are analyzing the costs and potential savings of cover cropping. Educators are also training young farmers to successfully use high tunnels.
Environmental benefits are a central focus. When tunnel coverings are replaced, exposed soils are vulnerable to rain, which can carry away phosphorus. By using legumes as cover crops instead of manure, nitrogen is added to the soil without excess phosphorus, creating a healthier and more balanced system.
While results vary across farms, researchers have already seen promising outcomes. Early trials show good crop growth and improved soil health. “Not surprisingly, we're finding a lot of variability and growth across the farms, and some outstanding cover crop production,” said Grossman. “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.”
Photo Credit: university-of-minnesota
Categories: Minnesota, Crops, Fruits and Vegetables