Lee Klossner and Paulo H. Pagliari, University of Minnesota-Twin Cities, Lamberton, MN
This study evaluated the effects of beef manure compost (compost) and overwintering hairy vetch cover crop (vetch) on soil fertility and variety performance under organic high tunnel. Treatments studied were vetch seeded at 35 kg ha-1; compost applied at 100 kg N ha-1, and compost (50 kg N ha-1) + vetch (35 kg ha-1). Vegetable crops grown included lettuce, cucumbers, tomatoes, and peppers. Lettuce yield was greatest in the compost treatment. Cucumber yield was variable, but was highest where either compost or compost+vetch treatments. Determinate tomatoes yielded highest when grown in the vetch treatment; while indeterminate tomatoes had mixed results with Cobra yielding highest in the vetch treatment and Better Boy yielding highest in the compost treatment. For pepper, Ace yielded highest in the vetch treatment, while Carmen yielded highest in the compost treatment. The soil samples collected in the spring 2012 showed that the fertility levels varied based on the previous crop and treatment. The vetch treatment provided more than 100 kg N ha-1 to the beds that were cropped to determinate tomatoes in the 2011. In contrast, some beds that received compost and compost+vetch treatments showed N immobilization from vetch, based on nitrate levels from fall 2011. Among all nutrients measured in the soil, nitrate and sodium were the ions that accounted for more than 90% of the dissolved salts in the soil solution, and therefore, were the ions that affected the most soil EC. Phosphorus levels were lowest in the vetch treatment (44 ppm) treatment compared with the compost and compost+vetch treatments (162 ppm). Nutrient accumulation in the soil inside the high tunnels may lead to unfavorable fertility levels for crop production. In summary, the research conducted in the high tunnels at SWROC showed that managing soil fertility is key in maintaining sustainability and profitability for organic growers.