Legume Cover Crop Management in High Tunnels for Soil Health and Fertility.

High tunnels are increasingly used for season extension in the Upper Midwest. However, intensive planting, irrigation, and fertilization to optimize high-value growing space have the potential to degrade soil health in high tunnels. This project evaluated the use of legume cover crops as a management tool for high tunnel soil health improvement and nitrogen fertilization. Three cover crop treatments 1) red clover monoculture, 2) Austrian winter pea/winter rye bi-culture, and 3) hairy vetch/tillage radish/winter rye tri-culture, compared to a bare ground control, were planted in three replicates and repeated in three high tunnels across USDA hardiness zones 3b, 4a, and 4b in Minnesota for two consecutive years (Fall 2015-Summer 2016 and Fall 2016-Summer 2017). In both years, cover crops were planted in late August, terminated and incorporated in early May, and followed by bell peppers, with no added fertility. Cover crop biomass, weed biomass, and soils were sampled before cover crop termination and soil was sampled again two weeks after termination. Peppers were harvested weekly August-September. Treatments were evaluated for cover crop and cash crop productivity and effect on soil health parameters, specifically cover crop biomass, percent carbon and percent nitrogen, marketable pepper yield, potentially mineralizable nitrogen, permanganate-oxidizable carbon, pH and EC. Two years of data will be presented, collection and analysis of year two data is underway. Preliminary results show that legume cover crop biomass varied by year, site, and cover crop treatment with red clover producing higher legume biomass than hairy vetch and Austrian winter pea. In both years cover crop treatments with rye had significantly lower weed biomass than the cover crop treatment without rye. For pH, EC, and marketable pepper yield in year one, site was a significant factor while cover crop treatment had no effect.