Compost, Cover Crops, and Mulch Effects in Organic Vegetable Systems

This multi-disciplinary project addresses critical stakeholder needs for improving organic vegetable farming practices to optimize pest management, crop quality, and profitability, while enhancing soil quality to help mitigate global climate change. Six cropping system treatments with different management practices were examined in Iowa: four treatments using cover crops (CC) and two without CC. Of the four CC treatments, two were treated as organic no-till (cover crop rolled) and two were tilled prior to vegetable crop planting/transplanting. Compost and mulch were applied to a sub-set of these treatments to test the effect of soil amendments. In 2012, peppers and sweet corn were grown, with plant growth, yields, and pests assessed throughout the season. Using lysimeter measurements, leached nitrate-N concentrations were determined throughout the growing season. Organic no-tillage crops performed better in 2012 than in 2011, with no-tillage peppers averaging 5,532 lb/acre compared to 8,012 lb/acre in tilled yields. Mulch provided an advantage to pepper yields, with mulched pepper plots averaging 9,385 lb/acre, while non-mulched averaged 6,640 lb/acre. No-tillage sweet corn failed to compete with mulched and tilled yields, averaging 2,472 lb/acre. Tilled and mulched yields were excellent, with tilled sweet corn plots producing 4,545 lb/acre, and mulched yielding 4,423 lb/acre. While the tilled crops were more productive, the mulched and no-till peppers had higher quality fruit, due to the straw or mulch barrier affording greater protection from soil particles. Several factors impacted no-tillage sweet corn production: a severe drought that required irrigation for survival; extreme heat, which decreased pollination; and poor emergence. The greatest benefits from cover crops in these vegetable systems appear to be related to improvements in soil and water quality. After the first season in Fall 2011, soil nitrate was lower in lysimeters in tomato plots under cover crop treatments than in plots without a cover crop. Without a cover crop, the non-mulched tomato treatment had more nitrate than the mulched plots. In the onion plots, the non-mulched plots had more nitrate for both cover crop and no cover crop treatments. In both the tomato and onion plots, there was more phosphorus in tilled vs. no-till treatments, probably due to tillage stimulating the mineralization of organic phosphorus from added compost. Both phosphorus and electrical conductivity were lower in the no compost treatments. The importance of biologically active organic matter was demonstrated by the particulate organic matter carbon representing 15.4% of total soil organic carbon averaged across treatments.