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以三峡库区王家桥小流域为例，探讨了应用地理信系系统（ＧＩＳ）和数学模型相结合评价土壤肥力的途径。通过系统全面的考虑选取了９个评价指标，应用层次分析法确定其权重，并用模糊数学建立单因子评价模型，再用加权法得到每个评价单元的土壤肥力综合评价指数（ＳＩＦＩ）。根据ＳＩＦＩ值将土壤肥力分为高（＞０．４５）、中（０．２５～０．４５）和低（＜０．２５）３级。应用ＩＤＲＩＳＩ对王家桥小流域的土壤肥力资源进行了分析。结果表明：王家桥小流域的土壤肥力大多处于中下水平，高、中、低肥力土壤的面积比例分别为２４．９％，３１．９％和３８．０％。流域的土壤肥力资源尚有较大的潜力。限制王家桥小流域土壤肥力资源的主要因素是土壤侵蚀、投入水平低。
Taking Wangjiaqiao watershed in the Three Gorges Reservoir area as an example, the ways to evaluate soil fertility by using the combination of GIS and mathematical models are discussed. Nine evaluation indexes were selected through system comprehensive consideration, and their weights were determined by AHP. One-factor evaluation model was established by using fuzzy mathematics. Then the comprehensive evaluation index (SIFI) of soil fertility of each evaluation unit was obtained by weighted method. Soil fertility was divided into high (> 0.45), medium (0.25-0.45) and low (<0.25) Grade 3 according to SIFI. Using IDRISI, the soil fertility resources in Wangjiaqiao watershed were analyzed. The results showed that most of the soil fertility in Wangjiaqiao watershed was at middle and lower levels, and the areas of high, medium and low fertility soils were 24.9%, 31.9% and 38.0% respectively. The soil fertility resources in the basin still have great potential. The main factor limiting the soil fertility resources in Wangjiaqiao watershed is soil erosion, with low input level.