Nutrient runoff and leaching under various fertilizer treatments and pedogeographic conditions: A case study in tobacco (Nicotiana tabacum L.) fields of the Erhai Lake basin, China

To ensure water security, it is crucial to understand the characteristics of nitrogen (N) and phosphorus (P) in water and to reduce their inputs. We conducted a 2-year trial (2021–2022) in tobacco fields across three sites in the Erhai Lake basin, China, to comprehensively measure and summarize N and P loss through runoff and leaching for four fertilizer treatments: no fertilizer (CK); farmers' traditional organic fertilizer (FP); chemical fertilizer (CF); and a combination of organic and inorganic fertilizer (OIC). The highest N concentrations were detected in leachate in the early tobacco growth stage, whereas the highest P concentrations occurred in runoff in the middle growth stage. Compared to FP, the OIC treatment improved nutrient uptake in flue-cured tobacco, while also reducing N loss through runoff and leaching by 45.37% and 19.34%, and reducing P loss by 7.22% and 8.26%, respectively. Correlation analyses revealed positive relationships of nutrient loss with soil organic matter content and nutrient inputs; elevation and soil water content exhibited varying correlations with different nutrients. These findings provide a theoretical foundation for the effective management of agricultural non-point source pollution in the Erhai Lake basin and shed light on water pollution pressures worldwide.