Short-term nitrogen mineralization from warm-season cover crops in organic farming systems

Further understanding the factors which influence cover crop decomposition is needed to tailor management practices to achieve production and environmental stewardship goals. Short-term Nmin from warm-season cover crops in organic farming systems was assessed with a variety of field and lab-based measures including: residue biochemical composition, extractable inorganic N, ion-exchange resin membranes, potential Cmin and Nmin. Residue biochemical composition and environmental conditions appeared to be the primary factors affecting short-term Nmin in our study. Legume-dominated cover crops demonstrated greater potential Nmin than grass cover crops with higher C:N ratios. However even cover crops with C:N ratios >40:1 were predicted to result in mean net Nmin rather than immobilization. Sorghum-sudangrass demonstrated a greater ability to moderate nitrate loss from the top 0–15 cm of soil over the fall season compared to the other cover crops evaluated. The difference in potential Nmin of low and high C:N ratio cover crops was not as appreciable as expected. Our data suggests that the microbial community reduced its carbon use efficiency (CUE) due to suboptimal soil moisture. Further investigation into the impacts of soil moisture on residue decomposition in agroecosystems is needed to better understand and manage short-term C and N cycling.