Sustainable nitrogen management in rice systems: trade-offs between productivity, nitrogen efficiency and greenhouse gas emissions

Climate change challenges rice production to sustain yield while improving nitrogen-use efficiency and reducing environmental impacts. Yet the role of stage-specific nitrogen management across diverse rice systems remains unclear. Here we evaluated nitrogen management scenarios under historical and future climates. RiceGrow, DSSAT-CERES-Rice and ORYZA v3 were calibrated on agro-meteorological observations, and literature-derived field trials benchmarked their nitrogen responses. RiceGrow was then coupled to machine-learning emulation and multi-objective optimization in a transferable framework, with yield constrained to at least 90% of the simulated maximum. Under historical climate, optimized practice reduced subregion-mean nitrogen inputs by 15% to 37% and raised agronomic efficiency of nitrogen (AEN) and gross margin by 10 to 21 kg·kg -1 and 0.3 to 2.5 ×10 3 USD·ha -1 , relative to farmers' practice. These gains required one to two additional splits, with greenhouse gas emissions (GHGs) varying from a 6% decrease to a 26% increase, a range driven by total nitrogen and yield rather than by stage reallocation. The framework consistently favored mid-season topdressing over large basal applications, although the specific split percentages are conditional on the backbone model. Future climate altered nitrogen demand unevenly, decreasing optimal nitrogen rates by 2% for middle-lower Yangtze single rice and 12% for late rice, but increasing them by 12% in other single-rice subregions and 19% for early rice. Within this modeling framework, soil properties accounted for the largest unique share of variation in optimized practice. Shifting nitrogen from basal dressing to mid-season topdressing offers a practical pathway to climate-resilient rice production, though GHG mitigation in some subregions depends on complementary water-regime and residue management.