Assessment of the N₂O emission reduction potential in greenhouse vegetable fields based on the DNDC model

The large amount of N₂O emission associated with high water and fertilizer inputs in greenhouse vegetable fields has become a salient issue. As N₂O is one of the major greenhouse gases, the research on reducing N₂O emissions can provide not only a reference for the formulation of carbon reduction plans for greenhouse vegetable fields but also a scientific basis to realize China’s “dual carbon” target. In this study, the N₂O emission of a typical greenhouse cucumber-tomato system in the Beijing suburbs was studied by using field monitoring and the DNDC model. The model was calibrated using field observations, and farmers’ conventional practices were set as the baseline scenario. The scenarios with changes in field management practices (e.g., irrigation method, N application rate, and replacement of chemical fertilizer by organic fertilizer) and regulation of soil physicochemical properties (soil organic carbon, pH, etc.) were set. N₂O emissions were obtained from 1250 simulations of the DNDC model for single scenario and multiple combinations of scenarios, and their emission reduction potentials were evaluated. The results showed that the DNDC model can simulate the soil temperature, soil water-filled pore space, vegetable yield, and N₂O emissions in greenhouse vegetable fields. The total N₂O emissions in the baseline scenario were 12.18 kg(N)∙hm⁻². The variation in the N₂O reduction potential of greenhouse vegetable fields ranged from 12.23% to 17.58% under the single-factor scenario. The sensitivity index showed that N₂O emissions were more sensitive to soil pH regulation and fertilizer reduction than to the other scenarios, with N₂O emissions (10.28 kg(N)∙hm⁻²) reduced by 15.60% and 14.86% for the 1.2-unit-change-in-soil-pH scenario and the 30% fertilizer reduction scenario (10.38 kg(N)∙hm⁻²), respectively, compared to the baseline. The multiple combination scenarios showed that a reduction of 31.69% in N₂O emissions from the baseline could be achieved with a combination of drip irrigation, 30% reduction in chemical N application, and 30% reduction in organic fertilizer. The N₂O reduction potential further improved to 55.58% (6.77 kg(N)∙hm⁻²) for the same combination in the low soil organic carbon and high pH soil scenarios. Overall, the DNDC model can simulate the field environment and overcome the drawbacks of limited treatment settings and high monitoring costs in field experiments, providing a useful method to quantitatively assess and reduce N₂O emissions in greenhouse vegetable fields. The combination of regulating soil physicochemical properties and optimizing water and fertilizer management can effectively reduce N₂O emission in greenhouse vegetable fields.