Soil Carbon and Nutrient Changes Under Soil Erosion and GIS-Based Simulation

After models of soil carbon and nutrient change, and soil erosion have been constructed, soil carbon and nutrient changes under soil erosion in each land unit of Wangjiaqiao watershed have been simulated and forecasted, which are based on IDRISIW GIS. The results of simulation showed that different element of soil nutrient (C, N, P, K) has different soil acceptable erosive modulus in different land use types, which means that one kind of soil element will decrease when soil acceptable erosive modulus is higher than the limited value. Since 1980's, much attention was paid by soil scientists to that soil erosion affects soil productivity in the world, most of which was focused on expansion of soil erosion and its influence on soil resources reproduction. The process of erosion affecting productivity is a very slow one and is not easy to be examined (Li 1986). The research of it is almost suspended for difficulties of its check-up. Soil nutrient loss is a main approach by which soil erosion affects productivity. At present, most researches were calculating the gross of nutrient loss from surface runoff, underground runoff or sediments, which cannot clearly illuminate the process and exact degree of that erosion affects productivity in each land unit in watershed and tortured the relationship between erosion and responding decline of productivity. Therefore, in order to prove mechanism of that erosion affects productivity it is very important illustrating the process and exact degree of that erosion affects soil carbon and nutrient.