The support practice factor (P) is the soil-loss ratio with a
specific support practice to the corresponding soil loss with upand-
down slope tillage (Renard et al., 1997). The major soil
conservation techniques used in the TGA are contour tillage
(CT), contour farming with a seasonal no-till ridge (CTN), and
level terraces. The P values for common support practices used
in the TGA were obtained from experimental data under
runoff-erosion plots under different support practices using
both natural and simulated rainfalls (Du and Shi, 1994) and are
listed in Table 2. The P value for individual map units was
determined according to the conversation practices obtained
from the field survey. If a new conservation practice was
recommended to the unit, a new P factor was assigned to the
database accordingly.