Effect of Cover Crop Termination Approaches on Soil Organic Matter Pools and Enzyme Activity in Organic Cropping Systems.

Legume cover crops are a critical component of organically managed systems, with the organic matter added at termination contributing to soil nitrogen (N) through N-fixation, soil microbial decomposer enzymatic activity, and pools of organic matter that can aid in improving soil physical properties over time. Specifically, particulate organic matter (POM) is a robust indicator of the degree to which a cover crop contributes to the actively decomposing labile organic matter pools. Organic growers commonly rely on cover crop mowing followed by soil incorporation to terminate legumes in the spring, a process resulting in losses of soil organic matter and soil structure. This study determined effects of two winter annual legume cover crops (Austrian winter pea and hairy vetch) terminated using four methods (flail mowing, disk tillage, organic herbicide and roller-crimping) on particulate organic matter pools and enzyme activity following termination at two sites in North Carolina.  Activity of four enzymes (exoglucanase, β-glucosidase, and β-glucosaminidase) associated with decomposition was also assessed. In two out of three site-years hairy vetch plots contained greater POM-C than Austrian winter pea and the no-cover crop control plots following termination. The site year, hairy vetch contributed equal quantities of POM-C to the no-cover crop control, likely due to labile C contributed from weeds. Cover crop termination method did not significantly inpact labile soil carbon pools. Soil enzyme activity (exoglucanase, β-glucosidase, and β-glucosaminidase) appeared to be more responsive to cover species than to termination methods, with Austrian winter pea showing the greatest positive effects on nitrification potential, β-glucosidase, and β-glucosaminidase.