Grain for green mitigates climate-driven increases in nitrogen loss from agricultural nonpoint sources and N₂O...

Nitrogen loss is a key process in the nitrogen cycle, and agricultural nonpoint sources (ANPS) and nitrous oxide (N₂O) emissions are two main pathways of agricultural nitrogen loss. In this study, a simulation framework for agricultural nitrogen loss in a watershed was constructed by coupling the ANPS model (the Soil and Water Assessment Tool, SWAT) with the N₂O emission model (the spatial reference nonlinear model, SRNM) under different future scenarios. The results confirmed that ANPS and N₂O emissions were the two main pathways of agricultural nitrogen loss in the watershed and that excessive application of nitrogen fertilizers to cropland was the most significant reason for nitrogen loss. From 2020 to 2070, agricultural nitrogen loss decreased by approximately 49.31 %, whereas the proportion of nitrogen loss from N₂O emissions increased from approximately 42.07 % to 63.25 %. However, the nitrogen loss rate from N₂O emissions decreased overall and decreased from 3.12 kg N/ha to 2.81 kg N/ha. Cropland was the main source of nitrogen loss, and every 1 % reduction in cropland area resulted in a 0.64 % decrease in nitrogen loss. The implementation of the Grain for Green (GFG) Program can reduce total nitrogen loss by 14 %. However, high rainfall and high temperatures in the future may increase nitrogen loss. The results revealed that under Representative Concentration Pathways (RCP)8.5 the rainfall was 3.2 % and temperature amplitude was 200 % greater than those under RCP2.6, respectively, and nitrogen loss was 14.8 % higher. Intensified rainfall primarily promotes ANPS nitrogen loss associated with surface runoff, while high temperatures exacerbate the N₂O emission process. However, GFG could control the increase in agricultural nitrogen loss from ANPS and N₂O emissions caused by high rainfall and temperature.