Effect of Legume Cover Crops and Spring Termination Practices on Soil Organic Matter and Aggregate Stability.

Organic agroecosystems rely heavily on soil organic matter (SOM) to provide nutrients to crops.  Roller-crimper termination of weed-suppressive cover crop stands has recently become a promising option both for obviating tillage and killing cover crops in a timely manner. Cover crops, particularly winter legumes, also provide significant nutrient inputs and a substantial C source to maintain or increase SOM. The objective of this project was to determine the effect of spring termination methods and cover crop species on labile C pools that are indicative of long term organic C trends. Three termination treatments (flail mowing, disk tillage, and rolling-crimping) of three winter ground covers (hairy vetch, crimson clover, and a bare ground control) were examined for their effects on soil microbial, chemical, and physical parameters. Cover cropping with either hairy vetch or crimson clover increased microbial biomass carbon (MBC), but did not have an effect on soil aggregation. The detrimental effects of disking on soil structure were observed within bare ground plots as a decrease in aggregate mean weight diameter, while aggregate stability remained the same between disked and no-till plots planted within either cover crop.  Disking also increased the amount of C and N vulnerable to mineralization compared with flail mowing, likely through the disruption of soil aggregates. Hot-water soluble carbohydrates, an indicator of exopolysaccharides responsible for aggregation, were not affected by the treatments. Surprisingly, there also were no differences in MBC among termination treatments. These two findings may explain the lack of a significant main effect of termination on aggregate stability.