Enhancing fertilizer nitrogen environmental safety and soil sustainability: The role of no-tillage with straw mulching in maize production

The fixation/immobilization and release/remineralization of fertilizer-derived mineral nitrogen (N) to fixed ammonium (NH4+) and organic N pools are crucial in fertilizer utilization and crop N uptake. Although straw mulching reduces the gaseous and leaching losses of fertilizer N from farmlands, the dynamics of fertilizerderived fixed NH4+ and organic N and their roles in fertilizer N retention and supply in soil-crop systems remain unclear. This study utilized 15N-isotope labeling in Northeast China to assess how conventional ridge tillage (RT) and no-till systems with different straw mulch levels (NT0, NT33, NT67, and NT100) affect the accumulation and release of fertilizer-derived fixed NH4+ and organic N. Compared to RT and NT0, no-tillage with straw mulching increased the conversion of fertilizer N to fixed NH4+ and organic N by an average of 15.3 % and 36.5 %, respectively, at a soil depth of 0-40 cm during the maize seedling stage. The higher net release of fertilizer-derived fixed NH4+ (average of 94.1 %) in a 0-40 cm soil layer suggested a high short-term N supply potential from this source during the growing season. Conversely, the limited net release of fertilizersourced organic N via remineralization during the vegetative phase (average of 51.3 %), coupled with the net re-immobilization of fertilizer N from the tasseling to ripening stages (average of 22.9 %), indicated a long-term N supply capacity of fertilizer-derived organic N for subsequent crops. No-tillage combined with straw mulching significantly enhanced fertilizer N use efficiency and maize yield by averages of 10.2 % and 14.8 %, respectively, compared to those of RT and NT0, demonstrating the effectiveness of these practices in optimizing fertilizer application and ensuring high crop productivity. Moreover, these conservation tillage practices enhanced fertilizer utilization and achieved sustainable agricultural outcomes by regulating the conversion and release of fertilizer N to soil-fixed NH4+ and organic N pools and by improving other soil properties.