assessing the effects of erosion on long-term soil productivity potential in kohin watershed, ghazvin province

maintaining soil productivity is one of the key factors in sustainable agriculture. soil erosion reduces soil productivity over a long-term period of time. therefore, determining soil erosion tolerance is necessary for sustainable agriculture production. in this study, the long-term effects of erosion on soil productivity in the typical kohin watershed were evaluated. the soil productivity index (pi) was used to predict long-term changes in productivity caused by erosion. both organic matter content and available water content significantly decreased due to increasing soil depth. therefore, they had the highest impact on soil productivity index. estimated average of annual erosion rate using cesium method was about 44 ton/hectare/ per year. the results showed that soil productivity index decreased about 2 percent annually by current erosion rate. calculated tolerable erosion rate based on 5 percent reduction in soil productivity over 100 years as standard level varied from 3 to 6 ton/hectare/ per year.