Temporal erosion-induced soil degradation and yield loss

Intensification of tropical agricultural systems by increasing fertilizer input and technology is a current trend in developing regions. Under intensive management, erosion impacts on crop productivity may not be detected in the short term. However, long-term impacts are expected because erosion rates in tropical agroecosystems are usually greater than the rate of soil formation. A temporal function of soil-depth change was defined and named life rime. Conceptually, soil's life time is the time until a minimum soil depth needed for sustaining crop production is reached. The life-time function was applied to the Ceveiro watershed (1990 ha) located at the Southeastern part of Brazil, and compared with sugarcane (Saccharum officinarum L.) yield loss estimations. Soil erosion prediction was made employing the Water Erosion Prediction Project. The mean soil erosion rate for the area was 15 Mg ha(-1) yr(-1), and sugarcane showed the highest mean value of 31 Mg ha(-1) yr(-1). The half life time of the watershed, i.e., the time until 50% of the area reach the minimum soil depth, was estimated to +563 yr in relation to present time. The estimated time for sugarcane's productivity to be reduced to 50% of the present value (half yield life time) was +361 yr. The life-time function was similar to the estimated long-term impacts of soil erosion on crop productivity. Therefore, the life-time function was considered as an integrative indictor for agricultural sustainability, useful for land-use planning and for the definition of tolerable soil erosion.