For a specific soil, the maximum average annual soil loss expressed as tons per acre per year that will permit current production levels to be maintained economically and indefinitely; the soil loss tolerance level. T values range from 2 to 5 tons per acre per year. According to the 1992 national resources inventory, about 63 million acres of highly erodible cropland are still eroding at more than their T value, including 21 million acres that are still eroding at three times T.