中文摘要：

论文在分析了农耕地土壤侵蚀速率改变后土壤中210Pbex，含量变化的基础上，检讨了现行的计算农耕地土壤侵蚀速率210Pbex法存在的问题误区。根据质量平衡原理建立了农耕地土壤210Pbex含量对侵蚀速率变化的响应模型，证明长期以来普遍认为的210Pbex法测定值为100a或200a以来的较长期的平均土壤侵蚀速率”的看法是不正确的。并用模型模拟计算了侵蚀速率变化后农耕地210Pbex含量的响应过程，结果表明农耕地土壤侵蚀速率发生变化后，土壤的210Pbex面积活度迅即响应，随着时间的增加呈指数变化。侵蚀速率增大的，土壤中210Pbex面积活度降低；减小的210Pbex面积活度增加.210Pbex可以替代137Cs用于农耕地土壤侵蚀速率的测定210Pbex不但可以测定持续耕种100a以上农耕地的侵蚀速率，也可以用于调查近期土地利用变化的土壤侵蚀响应。

英文摘要：

Based on analysis of the variation of 210Pbex inventory in soil of cultivated land in response to changes in soil erosion rate, mistakes in calculation of soil erosion rate of cultivated land using the 210Pbex method are discussed. A model is established to fit response of 210Pbex inventory to variation of soil erosion rate in soil of cultivated land, based on the principle of mass balance, demonstrating that the long-commonly-held assumption that what is determined with the 137Cs method is the mean soil erosion rate of the past 40 a or 50 a and with the 210Pbex method the mean of a longer past of 100 a or 200 a is incorrect. The model is used to fit response of 210Pbex inventory to the variation of soil erosion rate from 0. 06 cm a-1 to 0.6 cm· a^-1 and from 0. 6 cm a^-1 to 0.06 cm ·a^-1 The results indicate that 210Pbex inventory responds quickly, which rises or reduce exponentially with time, but negatively with soil erosion rate. Consequently,210Pbexcan replace 137Cs in determining soil erosion rate in cultivated land not only 100 years old, but also just a few years old due to change in land use.