A global meta-analysis of yield-scaled N 2 O emissions and its mitigation efforts for maize, wheat, and rice.

Maintaining or even increasing crop yields while reducing nitrous oxide (N ₂ O) emissions is necessary to reconcile food security and climate change, while the metric of yield-scaled N ₂ O emission (i.e., N ₂ O emissions per unit of crop yield) is at present poorly understood. Here we conducted a global meta-analysis with more than 6000 observations to explore the variation patterns and controlling factors of yield-scaled N ₂ O emissions for maize, wheat and rice and associated potential mitigation options. Our results showed that the average yield-scaled N ₂ O emissions across all available data followed the order wheat (322 g N Mg ^-1 , with the 95% confidence interval [CI]: 301-346) > maize (211 g N Mg ^-1 , CI: 198-225) > rice (153 g N Mg ^-1 , CI: 144-163). Yield-scaled N ₂ O emissions for individual crops were generally higher in tropical or subtropical zones than in temperate zones, and also showed a trend towards lower intensities from low to high latitudes. This global variation was better explained by climatic and edaphic factors than by N fertilizer management, while their combined effect predicted more than 70% of the variance. Furthermore, our analysis showed a significant decrease in yield-scaled N ₂ O emissions with increasing N use efficiency or in N ₂ O emissions for production systems with cereal yields >10 Mg ha ^-1 (maize), 6.6 Mg ha ^-1 (wheat) or 6.8 Mg ha ^-1 (rice), respectively. This highlights that N use efficiency indicators can be used as valuable proxies for reconciling trade-offs between crop production and N ₂ O mitigation. For all three major staple crops, reducing N fertilization by up to 30%, optimizing the timing and placement of fertilizer application or using enhanced-efficiency N fertilizers significantly reduced yield-scaled N ₂ O emissions at similar or even higher cereal yields. Our data-driven assessment provides some key guidance for developing effective and targeted mitigation and adaptation strategies for the sustainable intensification of cereal production.
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