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Free keywords:
deficit irrigation, nitrous oxide emissions, crop yield, optimal water and nitrogen inputs
Abstract:
Deficit irrigation, which is defined as irrigation below the crop water demand, constitutes a promising irrigation strategy for conserving water resources while maintaining agricultural production. However, its effect on the trade-off between crop yields and nitrous oxide (N2O) emissions remains uncertain, as is the optimal deficit irrigation ratio, which is defined as the difference between full and deficit irrigation divided by full irrigation. Here, we collected rigorously validated paired observations of crop yields and N2O emissions under deficit and full-irrigation conditions and conducted a global meta-analysis combined with multiobjective optimization to evaluate this trade-off and identify benchmark water and nitrogen (N) inputs. Overall, deficit irrigation did not significantly reduce crop yields but exerted contrasting effects on N2O emissions between rice and upland crops. Deficit irrigation generally increased N2O emissions from rice but reduced emissions from upland crops, particularly in regions with loamy soils and cold climatic conditions. The optimized deficit irrigation ratio and N input were 25.8% and 178 kg N ha− 1, respectively, for rice and 22.7% and 160 kg N ha− 1, respectively, for upland crops. These optimized inputs increased the yield of both rice and upland crops and decreased N2O emissions from upland crops. With respect to rice, although the total N2O emissions were not reduced, the optimized inputs minimized the N2O emission cost per unit yield increase. Additionally, we determined that the default methodology of the Intergovernmental Panel on Climate Change caused underestimation of N2O emissions from rice by 57.1% and overestimation of N2O emissions from upland crops by 20.4%. Our findings clarify the trade-off between yield and N2O emissions under deficit irrigation and provide benchmark values for water and N management, which is crucial for ensuring global food security and sustainable agricultural development.
