Modeling the response of agricultural non-point source pollution to planting structure and fertilization level in Erhai Lake Basin under low-latitude plateau climate

Agricultural non-point source (NPS) pollution is the major contributor to pollution in the Erhai Lake Basin in northeastern China. The key to the control of NPS pollution is optimizing the planting structures and fertilization regimes. However, the interplay between the three remains unknown, and to identify their interaction is of great importance for NPS pollution control. In this study, experiments with varied crop rotations and fertilization schemes were performed in Erhai Lake Basin, based on which eight response models between the planting structure, fertilization level and NPS pollution under the low-latitude plateau climate were innovatively proposed and verified. The major findings are as follows: (1) there are six main planting structures in Erhai Lake Basin, among which rice-broad bean rotation takes up the largest area (35.72% of the total planting area), followed by corn-broad bean rotation (which accounts for 28.64% of the total area); (2) structural equation modeling reveals that in the study area, the total nitrogen (TN) was the largest contributor to agricultural NPS pollution (R-2 = 0.90); while in rice-broad bean and corn-purple leaf lettuce rotations, total phosphorus (TP) was found to be the largest contributor to NPS pollution (R-2 > 0.37); (3) climate, irrigation, planting structure and fertilization affected the indicators of agricultural NPS pollution, among which climate had the greatest impact on the TN content, with a path coefficient of 0.87; irrigation had the largest impact on the ammonia nitrogen (AN) content, with a path coefficient of 0.62; fertilization also had the largest impact on the TN content, with a path coefficient of 0.67; the percentage of the planting structure area affected TP (0.21), TN (0.29) and chemical oxygen demand (0.24); the crop area significantly affected the content of TP (0.45), TN (0.42) and chemical oxygen demand (0.51); and the crop yield significantly affected the content of TN (0.57). The research provides theoretical support for the prevention and control of agricultural NPS pollution in Erhai Lake Basin.