Soil loss tolerance: Fact or myth?

THE concept of tolerable soil loss, as now applied in soil conservation programs, does not serve the long-term interest of mankind in assuring the indefinite productive capability of cropland. Why? Because soil loss tolerances—T values—presently assigned to cropland soils are based on faulty premises concerning rates of topsoil development and mineral weathering processes. The concept of soil loss tolerance rests upon two assumptions: first, that soil scientists can assess reliably and objectively the maximum rates of soil erosion that can be tolerated and, second, that policymakers can objectively weigh that assessment against countervailing interests or needs, however these may be defined. Both assumptions should be challenged. Short-term political considerations may demand that public policy allow soil resources to degrade, gradually but unceasingly, to a state of agricultural uselessness. But continued support of such a policy must clearly acknowledge the extent and quality of known information about soil development rates under agricultural conditions. Soil loss tolerance values are too important to continue to be based on what amounts to quasi-scientific folklore. The T-value concept The intense nationwide soil conservation movement, initiated in the United States in the 1930s, included a strong quest for practical knowledge …