氮素是农田土壤中最活跃的营养元素之一，同时也是日趋严重的环境污染因子，农田氮素流失对我国湖泊河流水体富营养化及水质的恶化构成了严重的威胁。迄今为止，综合考虑坡度和施氮量等因素对氮素径流损失的影响，并结合模型进行流域氮素径流损失的模型模拟，还缺乏系统、深入的研究。本项目以云南洱海流域作为代表性的高原农业研究区，选取水稻、油菜、玉米等主要典型作物，采用野外监测、田间试验、室内模拟以及模型模拟相结合的方法，研究不同氮肥用量、不同坡度对农田径流氮素损失的影响规律，应用SWAT（Soil and Water Assessment Tool）模型，在获取模型相关参数的基础上，对模型进行敏感性分析、校准与验证。通过模型模拟，从流域尺度上估算农田氮素径流损失量及其空间分布特征，明确洱海流域氮素径流损失的关键源区，解析影响机理，旨在为提高氮肥利用率、减少农田面源污染、保护高原湖泊洱海水环境安全提供依据。

Nitrogen is one of the most active agricultural soil nutrient elements, as well as a factor of the increasingly serious environmental pollution. Nitrogen runoff from farmland is an important contributor to water eutrophication and water quality deterioration of lakes and rivers. So far, there is little comprehensive research on the effects of slope and nitrogen fertilizer application on the nitrogen runoff using agricultural non-point source pollution model (Soil & Water Assessment Tool, SWAT）. The study area located in the Erhai Lake basin in Yunnan province which is a representative highland farming region. Rice, rape and corn crops were chosen as representative crops. The methods including field observation, field experiment, experiment simulation in lab and model simulation were used to study the effects of different nitrogen fertilizer applications and slopes on the nitrogen runoff. Based on the parameters obtaining from experiment, the sensitivity analysis, calibration and validation of model parameters had been conducted. Nitrogen runoff and its spatial distribution characteristics were estimated at the watershed scale and the critical source area of nitrogen runoff in Erhai Lake basin was identified based on model simulation. By this study, it could provide a basis for increasing nitrogen use efficiency, decreasing non-point source pollution of farmland and improving water quality of Erhai Lake.