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

Fixation/immobilization and release/remineralization of fertilizer-derived mineral nitrogen (N) to fixed ammonium (NH4+) and organic N pools play crucial roles in fertilizer utilization and crop N uptakes. Although straw mulching has been shown to reduce gaseous and leaching losses of fertilizer N from farmlands, the dynamics of fertilizer-derived fixed NH4+ and organic N and their roles in fertilizer N retention and supply in soil-crop system remain unclear. This study utilized 15N isotope labeling in Northeast China to assess the effects of conventional ridge tillage (RT) and no-till with different straw mulch levels (NT0, NT33, NT67, NT100) on the accumulation and release of fertilizer-derived fixed NH4+ and organic N. Our findings indicate that compared to RT and NT0, no-tillage with straw mulching increased the conversion of fertilizer N to fixed NH4+ and organic N by averaging 15.3% and 36.5% at the soil depth of 0-40 cm during the maize seedling stage, respectively. The higher net release of fertilizer-derived fixed NH4+ (averagely 94.1%) in the 0-40cm soil layer suggests a high short-term N supply potential from this source during the growing season. Conversely, the limited net release of fertilizer-sourced organic N through remineralization during the vegetative phase (averagely 51.3%), coupled with the net re-immobilization of fertilizer N from tasseling to ripening stage (averagely 22.9%), indicates a long-term N supply capacity of fertilizer-derived organic N for subsequent crop. No-tillage combined with straw mulching significantly enhances fertilizer N use efficiency and maize yields by 10.2% and 14.8% on average compared to RT and NT0, demonstrating the effectiveness of these practices in optimizing fertilizer application and ensuring high crop productivity. These conservation tillage practices enhance fertilizer utilization and achieve sustainable agricultural outcomes by regulating the conversion and release of fertilizer N to soil fixed NH4+ and organic N pools, and improving other soil properties.