For a specific soil, the maximum average annual soil loss expressed as tonnes per acre per year that will permit current production levels to be maintained economically and indefinitely. T values range from 2 to 5 tonnes 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.