The favor able natural condition is advantageo us to various land use patterns in low mountains and hills of south Jiangsu province.And various ways of land uses have changed the properties of the soil.In general,the soil erosion and the nutrient loss of the cultivated soil that are disturbed by human are larger than that of the uncultivated soil in natural or half-natural condition.In order to know the quantity of nutrient loss caused by soil erosion,the soil erosion intensity should be decided.The tracer method by cesium-137 can be used to resolve two problems.One is to determine the backg round content of ¹³⁷Cs.The other is to establish the model of soil erosion.After estimating the soil erosion rate of various ways of land uses,the quantity of soil nutrient loss is calculated.For the sake of indicating the potential risk of soil erosion,and comparing the danger of the loess with red soil area,the concept of the equal value soil erosion is put forward.It is preliminary found that cultivated soil,especially paddy,may be a primary agricultural source of nutrient elements of Taihu lake.