Intensive rice–wheat (RW) rotations in the Yangtze River Basin often rely on excessive nitrogen (N) inputs, leading to low N use efficiency and environmental risks. To test whether high productivity can be sustained with lower N inputs, a two-year field experiment was conducted in the Upper Yangtze River Basin to evaluate seasonal N allocation strategies across the annual rotation. A moderately reduced annual N input of 315 kg ha−1 maintained annual grain yields of 18.2–19.3 Mg ha−1, statistically comparable to traditional high-input practices using 360 kg N ha−1. Wheat yield was mainly determined by current-season N supply, and no significant yield carry-over effect of rice-season N input on subsequent wheat yield was detected. Instead, higher rice-season N input tended to increase nitrate accumulation in deeper soil layers, particularly at 40–60 cm. Optimized seasonal N allocation significantly improved the partial factor productivity of N while maintaining a positive apparent system N balance under full straw return. These results indicate that strategically limiting and reallocating seasonal N inputs according to crop demand can sustain high annual productivity, improve N use efficiency, and reduce potential N-related environmental risks in intensive RW rotations.
Li et al. (Wed,) studied this question.