Managing for soil organic matter in low input agroecosystems with cover crops and reduced tillage

Background/Question/Methods

Organic agroecosystems rely heavily on soil organic matter to provide plant nutrients.  However, intensive cultivation needed for weed control in organic production hastens mineralization of soil organic matter (SOM), highlighting the need for alternative weed control strategies.  Reducing tillage in organic systems through roller-crimper termination of weed-suppressive cover crop stands has recently become a promising option. Cover crops, particularly winter legumes, provide significant nutrient inputs and a substantial C source to maintain or increase SOM. Our objective was to determine the effect of spring termination method and cover crop species on labile C pools in an attempt to identify short-term indicators for long term organic C dynamics. We expect that in comparison to disk tillage, rolling-crimping will have less destructive effects on soil structure and foster a microbial community that promotes soil aggregation. We examined how three termination treatments (flail mowing, disk tillage, and rolling-crimping) of two legume cover crop species affect soil microbial, chemical, and physical parameters.

Results/Conclusions

Cover cropping with either hairy vetch or crimson clover significantly (by 42% and 34%, respectively) increased microbial biomass carbon, but did not have a significant effect on soil aggregation. Termination method of cover crops affected soil aggregation, with a significantly higher proportion of large aggregates under flail than disk. Soil bulk density was lower in disk tillage plots compared to both roll and flail termination. Surprisingly, there were no differences in soil microbial biomass among termination treatments. Cover crop species had a significant effect on MBC over 5-15cm soil depth, with higher MBC under crimson clover than hairy vetch. This likely reflects differences in root structure, biomass, and distribution. These results suggest that effective management of cover crops with spring termination along with appropriate legume species selection can better conserve soil organic C.