Photos Courtesy of Dr. Julie Grossman, University of Minnesota
High tunnels, also called hoop houses or poly tunnels, are an important and relatively inexpensive tool for horticultural production to extend seasonal crops in cold climates. However, their use creates challenges related to soil health and decreased crop yields.
There is no question that using high tunnels results in increased marketable crop yields and extended harvests, but there are concerns that continued use of these high tunnels will jeopardize the long-term sustainability due to the loss of natural resources in the soil.
The greater number of available growing days in high tunnels intensifies soil use due to longer and more frequent planting cycles and increased nutrient demands. These practices, coupled with high temperatures and irrigation under protected conditions, leaves high tunnel soils vulnerable to depletion of organic materials and increased soil salinity. Soil health depletion is a major concern for growers, especially those who are certified as organic.
The objective of a two-year study by researchers at the University of Minnesota was to explore the effect of winter cover crops on soil nutrients, soil health, and bell pepper crop yield in high tunnels. Cover crops are often used to manage soils issues, such as decreased organic matter, degraded soil structure, increased salinity, and high nitrogen needs.
The study was conducted from August 2015 to September 2017 at three sites in Minnesota. The cover crops used in this study consisted of red clover monoculture, winter pea/rye bicultural, hairy vetch/tillage radish/rye, and a bareground, weeded control. Researchers sought to identify productive winter cover crop mixtures in cold-climate high tunnel environments, to quantify the effects of overwintered cover crops on soil health, and to assess the impacts of overwintered cover crops on cash crop productivity-in this case, bell peppers.
During the study period, cover crops were seeded at two different times-either in late August/early September between standing rows of peppers, or in mid-September after the pepper plants had been removed. The cover crops were watered overhead as needed, and no additional fertilizer was added to any of the study plots. In May, the cover crops were mowed down, left to dry on the soil surface, and then tilled into the soil. New peppers were transplanted into the soil 5-10 days later.
Sowing cover crops later in the fall after pepper plants were removed generally increased total biomass from 30% to 70% that of the early planted plots, except at the warmest site. The legumes (winter peas) were winter hardy to zones 4a and 4b in the high tunnels, extending past their open-field range of zone 5a, and researchers will continue efforts to increase the number of surviving legumes in order to increase the nitrogen in the tunnel soil samples.
The researchers concluded that overwintered cover crops in high tunnels may be a possible organic alternative for crop producers to reduce the dependence upon compost and manure to meet nitrogen requirements and replenish organic soil matter. Further research will be needed to determine the potential trade-offs between cash crop and cover crop productivity.
According to Dr. Julie Grossman, Associate Professor at the University of Minnesota, "Now that some high tunnels have been on the landscape for almost 30 years, more farmers are coming to us with questions about how they can improve soil health in these unique environments. This project is the first step to understand the role that cover crops may play in improving long-term sustainability and productivity of high tunnel soils."
You can learn more about this exciting research by reading the full report in HortScienceDOI: https://doi.org/10.21273/HORTSCI15987-21
Established in 1903, the American Society for Horticultural Science is recognized around the world as one of the most respected and influential professional societies for horticultural scientists. ASHS is committed to promoting and encouraging national and international interest in scientific research and education in all branches of horticulture.
Comprised of thousands of members worldwide, ASHS represents a broad cross-section of the horticultural community - scientists, educators, students, landscape and turf managers, government, extension agents and industry professionals. ASHS members focus on practices and problems in horticulture: breeding, propagation, production and management, harvesting, handling and storage, processing, marketing and use of horticultural plants and products. To learn more, visit ashs.org.
