Soil Fertility Dominates the Optimal Allocation of Basal and Tillering Nitrogen in Rice Production

Excessive basal and tillering nitrogen (BTN) application in rice production causes substantial N losses and environmental costs, yet practical soil fertility thresholds to guide safe BTN reduction (RBTN) have not been established. This study combined meta-analysis with field experiments to determine these thresholds and elucidate underlying mechanisms. The meta-analysis showed that the BTN yield response was negatively correlated with soil total nitrogen (STN) and soil organic matter (SOM), with no significant RBTN yield penalty above 2.0 g kg−1 STN or 30 g kg−1 SOM. Field experiments in soils exceeding these thresholds demonstrated that zero BTN with optimized panicle N (90 kg ha−1 for indica; 120 kg ha−1 for japonica) increased indica yield by 3.6% while reducing N input by 62%, and maintained japonica yield with 50% less N. Nitrogen recovery efficiency rose from 35.5% to 86.1% in indica and from 42.0% to 55.8% in japonica. These improvements were physiologically underpinned by sufficient indigenous soil N supply for productive tiller formation and improved synchrony between panicle N application and crop demand. Collectively, these findings establish quantifiable soil fertility thresholds for safe early N reduction and demonstrate that BTN can be substantially reduced or even omitted in high-fertility soils without compromising yield—offering a simplified, efficient N management strategy for intensive rice production systems. The divergent compensatory pathways between indica and japonica rice further highlight the need for cultivar-specific calibration in future applications.