Integrated Management Reduces Drainage-Related Nitrogen Export and Sustains Yield in Direct-Seeded and Mechanically Transplanted Rice

Sustainable rice production requires management strategies that reduce drainage-related nitrogen export while maintaining grain yield under increasingly constrained water and labor conditions. This study evaluated a controlled-irrigation-based integrated management regime in direct-seeded and mechanically transplanted rice under production-field conditions in the lower Yangtze River region, China. The optimized regime combined threshold-based controlled irrigation, functional basal fertilizer, and key-stage foliar regulation, whereas the traditional treatments followed local conventional flooding and fertilization practices. Drainage-related total nitrogen (TN) export was mainly associated with rainfall or irrigation-overflow events after fertilization. Compared with the corresponding traditional treatments, optimized management reduced irrigation input by 28.5% and 26.4%, cumulative drainage volume by 54.8% and 46.5%, and monitored-event TN export load by 63.6% and 60.0% in mechanically transplanted and direct-seeded rice, respectively. Grain yields reached 10,088 and 9870 kg ha −1 in Opt-MT and Opt-DS, increasing by 6.5% and 7.2%, respectively. The optimized treatments also reduced chalky grain rate and chalkiness degree, although head rice rate did not improve synchronously. These findings provide field-based evidence that integrated management may help coordinate monitored drainage-related nitrogen-export mitigation, water-saving irrigation, and yield maintenance under similar production-field conditions.