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Cover Crops Provide Water Quality Benefits in Organic Vegetable System

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GREENFIELD, Iowa -An organic vegetable research study at the Iowa State University Neely-Kinyon Research Farm is showing big benefits from cover crops in terms of decreased nitrate leaching and improved soil carbon and organic matter.

The USDA-Organic Transitions Project is looking at the effect of cover crops, compost, no-till and mulch on organic vegetable production. Funded by USDA in 2010, the project examines ways to encourage organic transition by developing recommendations for vegetable cropping systems that maximize soil quality, foster carbon sequestration and minimize nutrient loss, said Kathleen Delate, ISU agronomy and horticulture professor.

Delate is leading the project with Cynthia Cambardella, who is with the USDA-ARS National Lab for Ag and the Environment in Ames.

Delate and Cambardella are collecting data through plot lysimeters, which are devices used to collect water and measure nitrate concentrations below the rooting zone.

The study looks at three tillage comparisons - tilled followed by straw much, tilled without straw mulch and organic no-till. Two organic fertility treatments are also being researched -composted animal manure alone and composted animal manure with cover crops.

Fall cover crops were planted in October 2012 at a rate of 25 pounds of hairy vetch and 90 pounds of rye per acre. Treatments were replicated four times for a total of 48 plots. Cover crops were disked under.

"Because we had extensive spring rains, the cover crops were not disked until June 8 and not rolled until June 20," Delate said. "We planted June 24, three weeks behind schedule."

Compost is applied at a rate of 100 pounds of nitrogen per acre each spring and organic fertilizer is side-dressed after vegetable crop establishment at 50 pounds of nitrogen per acre.   
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