CHANGE IN SOIL CHARACTERISTICS AFTER INCORPORATING COVER CROPS IN THE CROP ROTATION

Cover crops have the potential to improve soil-based ecosystem services by increasing vegetation cover and plant diversity, improving soil quality, increasing soil carbon and nitrogen stocks, and enhancing microbial activity. Planting cover crop mixtures in the cash crop rotation has been proposed to overcome possible cash crop productivity losses during the organic transition period. The first objective of this study was to examine the effects of three cover cropping systems on soil properties of potential importance for crop performance and cash crop yield following three years of an organic transition period prior to planting organic corn (Zea mays L.). The three-year crop rotation was a corn -soybean (Glycine max L.)-winter wheat (Triticum aestivum L.) rotation (CSWR). Four cover cropping systems were studied including a traditional cover crop system (TR), a mixture of cold susceptible cover crop species (WK), a mixture of cold tolerant species (WH), and a no-cover control (NC). Split block experiments were setup in four fields with contrasting topographical positions, namely depression, slope, and summit in each field. After the three-year transition period, there was no difference in particulate organic matter (POM), microbial biomass carbon, nitrogen mineralization rate, soil ammonium contents, and organic corn yield following the transition period, across the cover crop treatments. However, soil moisture, soil nitrate content, soil carbon mineralization rate, and aboveground plant biomass were significantly affected by cover crop treatments. Field topography influenced organic corn yield after the transition period, with the highest yiels in field depressions. The second chapter focused on a meta-analysis from 15 field studies that estimated the change in soil carbon sequestration due to cover crops and tillage systems. Four systems were compared: conventional tillage without cover crop (CT-NC), conventional tillage with cover crop (CT-CC), no-tillage without cover crop (NT-NC), and no-tillage with cover crop (NT-CC). NT-CC systems had the highest soil carbon sequestration whereas CT-NC had the lowest soil carbon sequestration. Tillage had a stronger influence on carbon sequestration compared to cover crops. In conclusion, cover crops have the potential to improve crop growth and important soil characteristics during the organic transition period and providing increased ecosystem services when combined with no-tillage.