Stover Mulching And Inhibitor Application Maintain Crop Yield And Decrease Fertilizer N Input And Losses In No-Till Cropping Systems In Northeast China

Microbial immobilization of nitrogen and mineral fixation of ammonium play important roles in the retention of fertilizer N in soil, and the subsequent microbial mineralization and abiotic release regulate N availability to crops. However, how fertilization management practices temporally influence the biological and abiotic processes of fertilizer N transformation remain unclear. Therefore, we conducted a field micro-plot experiment with N-15-labeled-fertilizer application in a long-term no-till maize cropping system in Northeast China to evaluate the effects of maize stover mulching alone and in combination with inhibitors on the conversion, crop use efficiency, and loss risk of fertilizer N. The following four treatments were established in our trial: (1) conventional NPK fertilization (NPK); (2) NPK plus maize stover mulching (NPKS); (3) 20 % reduced NPK plus maize stover mulching (RNPKS); and (4) RNPKS plus urease and nitrification inhibitors (RNPKSI). The results showed that the retention of fertilizer N was dependent on both soil depth and management practices at the seedling stage of maize. At the soil depth of 0-20 cm, maize stover mulching significantly enhanced the transformation of fertilizer N into fixed NH4+ and organic N pools by 49.9 % and 65.6 % compared with NPK. The reduction of NPK with maize stover mulching further promoted fertilizer N conversion into the organic N pool by 43.2 %, with a reduction in the fixed NH4+ pool by 32.0 %, while the combined with inhibitors application in RNPKSI treatment resulted in the opposite trend due to the extended residence of fertilizer-derived NH4+-N. Meanwhile, at a depth of 20-40 cm, maize stover mulching in NPKS and RNPKS treatments significantly improved the transformation of fertilizer N to the fixed NH4+ pool compared with NPK, and maize stover mulching and inhibitors application in RKPNSI treatment further increased this conversion compares with RNPKS. The subsequent mineralization and release of fertilizer-derived organic N and fixed NH4+ affected crop uptake of fertilizer N. The fertilizer N use efficiency (NUE) in the three maize stover mulching treatments was significantly improved by an average of 16.1 %, while its gaseous losses were remarkably reduced by an average of 32.8 % compared with NPK. These findings suggest that maize stover mulching and inhibitors application in RNPKS and RNPKSI treatments are efficient management strategies in no-till maize cropping system in Northeast China, reducing N input, maintaining crop yield, enhancing NUE, and potentially minimizing environmental pollution risk by regulating fertilizer N conversion between fixed NH4+ and organic N pools.