Relation of T Values to Conservation Technology and Other Factors
The soil-loss tolerance values set in the 1950s were based on the soil conservation technology available at the time that could be reasonably and profitably applied. By the mid-1980s, conservation tillage, based primarily on leaving residue from last year's crop on the soil surface, had been developed as a new erosion-control technology (Chapter 7). This technology largely replaced the widely used clean-till technology, and thus from one perspective,soil-loss tolerance values could be lowered because of the new conservation-tillage technology. However, when the 1985 Food Security Act was implemented, acceptable conservation systems (ACS) were identified that were based on double soil-loss tolerance values (2T) if ephemeral gully erosion was a problem in the field, or triple soil-loss tolerance values (3T) if ephemeral gully erosion was not a problem. Practices adopted from a list of ACSs (much like BMPs)were considered to be acceptable. A large number of farmers felt that achieving the soil-loss tolerance would cause too much economic hardship in the short run. These farmers had sufficient political clout to influence policymakers, resulting in the use of higher soil-loss tolerance values (2T or 3T) and a BMP-type approach of selecting from a list of "acceptable conservation systems.