Mechanisms of N2O Emission in Drip-Irrigated Saline Soils: Unraveling the Role of Soil Moisture Variation in Nitrification and Denitrification

Drip irrigation generates structural bodies in soil, forming layered structures with moisture content gradients. There are four typical soil moisture characteristic values in this concentric structure as saturation capacity (θs), field capacity (FC), 60% field capacity (60% FC), and 30% field capacity (30% FC). In this study, we simulated these four soil water characteristic values to conduct an indoor soil incubation experiment under three different incubation conditions: aerobic (O), aerobic with 10 pa acetylene (OC), and anaerobic (AO). The results indicate that in soil with saturated water content, denitrification under aerobic conditions leads to high N2O emissions; in soil at field holding capacity, nitrification under aerobic conditions dominates low N2O emissions, which is most conducive to N2O reduction and greenhouse gas emission mitigation; in soil with 60% of field holding capacity, denitrification under anaerobic conditions leads to high N2O emissions; and in soil with 30% of field holding capacity, microbial activity decreases, inhibiting nitrification, denitrification, and N2O emissions. Our research has found that when conducting aerobic drip irrigation in soil at field capacity (FC), denitrification was reduced by 99%, nitrification was increased by 70%, and microbial activity was enhanced by 5%. Therefore, during drip irrigation, the position and flow rate of the dripper should be controlled to reduce soil water saturation areas, maintain soil aeration, control soil moisture content below field holding capacity, promote the nitrification process, reduce N2O emissions, and improve soil nitrogen use efficiency. Our study elucidates the characteristics of nitrogen transformation and N2O emissions across various soil moisture contents within the soil water structure under drip irrigation conditions, providing a scientific basis for the formulation of precise irrigation management practices and strategies for efficient soil nitrogen utilization.