Quantitative Standard to Protect On-Site Soil Resources
The most widely used quantitative standard for conservation planning to protect on-site soil resources from excessive erosion is the soil-loss tolerance concept described in earlier chapters. Soil-loss tolerance "denotes the maximum level of erosion that will permit a high level of crop productivity to be sustained economically and indefinitely" (Wischmeier and Smith,1978). Conservation practices are selected to control average annual soil loss to a rate less than the soil-loss tolerance (T) value assigned to each specific soil. Because the objective is long-term soil maintenance, cumulative erosion over a long period, rather than erosion from a single or a few storms, is the basis for the soil-loss tolerance rate. High soil-loss rates are acceptable in any one year if the overall erosion rate is low.