Legume cover cropping has been widely used as an efficient strategy to improve soil fertility. Although this management practice is important to resolve N deficiency for the transition from conventional to organic production systems, optimization is necessary to determine legume cover crop species and termination methods. This study used soil microbial properties and processes to evaluate the suitability of several legume cover crops and termination methods for organic transition in southeastern USA. Soil samples were taken from two newly-established study sites, each containing 12 treatments of three termination methods (disk, flail, and spray) and four cover types (no cover crop, Austrian winter pea, hairy vetch, and crimson clover). Compared to disking and spraying, flail mowing significantly increased soil microbial biomass C by ~17%, C mineralization by ~25%, N mineralization by ~16%, and nitrification potential by ~36%, 12 weeks after cover crop termination. However, cover cropping only stimulated nitrification potential, but not C and N mineralization. Furthermore, the activities of soil enzymes (exoglucanase, β-glucosidase, and β-glucosaminidase) appeared to be more responsive to cover types than to termination methods. Among three cover crops, Austrian winter pea showed the greatest positive effects on nitrification potential, β-glucosidase, and β-glucosaminidase. The ratio of C mineralization to microbial biomass C also differed with cover types, being lowest in Austrian winter pea. Our results indicated that legume species even with small differences in C-to-N ratio and lignin and cellulose contents could have varied effects on soil microbial properties and processes. Nitrification potential, representing the function of a small group of soil microbial community, was proved to be sensitive to both legume species and termination methods.
Bibliographical noteFunding Information:
This work was financially supported by USDA grant 2011-51106-21872 . We thank Matthew Brown for providing biomass, C and N content data of cover crop residues and other members from Dr. Julie Grossman's lab for their generous assistance with fieldwork and site maintenance. We also thank the Soil Science Service Lab and Environmental Engineering lab, North Carolina State University, for allowing us to use equipment and for helping analyze chemical components of crop residues.
- Cover crop
- Flail mowing
- Legume species
- Nitrification potential
- Organic transition
- Soil enzyme activity