Quantifying nitrogen and phosphorus losses from crop and livestock production and mitigation potentials in Erhai Lake Basin, China

Crop and livestock production are the primary contributors to agricultural non-point pollution. It is crucial to understand the individual contributions of different crop and animal species to nitrogen (N) and phosphorus (P) losses in order to develop effective and practical mitigation options. This study aims to estimate the relative contributions of N and P emissions to water and air from various crop and animal species in the Erhai Lake Basin and identify corresponding mitigation potentials. We improved the Nutrient Flow in Food Chains, Environment, and Resources Use (NUFER) model by incorporating data from farmer surveys, monitoring data, and terrain data. Additionally, scenario analysis has been conducted to explore optimum reduction strategies. We found that the losses of N and P to water and air originating from crop and livestock production in the Erhai Lake Basin were 6.5 kt and 0.4 kt, respectively. In terms of crop production, vegetables, maize, and beans accounted for 53% and 55% of the total losses to the environment for N and P, respectively. In livestock production, dairy cattle and pigs accounted for 84% and 64% of the total losses for N and P, respectively. NH3 emissions, contributing to 48% of the N losses, have a dominant share, while the primary source of P loss was runoff and erosion, contributing to 74% of the total. Our scenario analyses suggest that losses of N and P can be reduced by 50% and 89% respectively, through balanced fertilization, optimized breeding management, and the prevention of direct discharge of animal manure into water. The outcomes of this study provide valuable insights into improving water quality and promoting sustainable agriculture at the basin scale.