ASSESSING SOIL PRODUCTIVITY IN RELATION TO LAND USE AND CONSERVATION

An approach to evaluating the long-term effects of erosion on the productive potential of the U.S. soil resource base is presented. This approach involves the application of a numerical index method for quantifying productivity to soil and land use data bases compiled by the Soil Conservation Service. The relative productive potential of soil was evaluated in terms of the environment it provides for root growth based upon the soil's available water capacity, resistance to root growth and development, and adequacy of pH to a depth of 100 centimeters.; An estimation of the effect of erosion on soil productivity in the Corn Belt at 25, 50 and 100 years of simulated erosion is presented. The weighted average loss in soil productivity is projected to be less than eight percent for any Major Land Resource Area (MLRA) in the Corn Belt over the next 100 years. However, the decline in productivity can be substantial for some soils in certain landscapes, especially where slopes exceed 6 percent. Deep fertile soils and the preponderance of cropland on nearly level to gently rolling terrain buffers the Corn Belt against productivity reductions over the next 100 years. The vulnerability of soils to productivity losses and the potential for reductions in productivity in each MLRA are also discussed.; Based on a concept of multiple T values, a method is presented to establish a quantitative basis for soil loss tolerance (T1) for maintenance of long-term soil productivity. The method determines a T value (T1) for a soil based on a measure of its productivity, its vulnerability to productivity losses from erosion, an allowable reduction in productivity, and a planning horizon in years. Soils with low vulnerability to erosion losses in productivity will have soil loss tolerance (T2) determined by other erosion concerns. The method has broad application and requires only that the index of soil productivity used is normalized to a range of 0.0 to 1.0.