Optimizing nitrogen fertilization rate to achieve high yield and high soil quality in paddy ecosystems with straw...

Plastic film mulching is a potentially water-saving cultivation strategy, while straw return coupled with nitrogen (N) fertilization can ensure sustainable soil productivity and increased soil organic matter (SOM) sequestration. Nevertheless, a comprehensive understanding of how soil quality and agronomic productivity respond to long-term N fertilization and straw incorporation practices under non-flooded conditions with plastic film mulching remains elusive. Herein, a 15-year field experiment with straw incorporation practices (straw return and no straw return) under various N fertilization rates (N0, N1, N2, N3, and N4: 0, 45, 90, 135, and 180 kg N ha^-1, respectively) was conducted to explore their long-term effects. Compared with N0, N fertilization significantly improved rice yield (52.2-74.0%) and plant N uptake (50.1-96.8%). Effective panicle density was the primary component affecting rice yield under different N conditions. However, N use efficiency was lowest under 180 kg N ha^-1. N fertilization primarily impacted rice yield by directly supplying N for rice growth, accounting for 79% of the rice yield variation. The modest enhancement in rice yield resulting from straw return was attributed to its positive effects on soil physicochemical properties. Straw return increased alkali-hydrolyzable nitrogen, Olsen-phosphorus, and NH₄OAc-exchangeable potassium by 3.4%, 10.4%, and 38.5%, respectively. N fertilization rates altered the impact of straw return on SOM; SOM increased in N2 and N4 under straw return, whereas no difference was observed between the straw management groups under N0, N1, or N3 fertilization. Moreover, while higher N fertilization rates decreased the soil quality index (SQI), straw return offset this negative effect. Considering rice yield, N use efficiency, and SQI, straw return treatment coupled with N application rate of 135 kg ha^-1 was deemed suitable for sustainable rice production with plastic film mulching.