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16 A sensitivity analysis was dame on the calculation for the K value. The psramete*s used to calculate K axe silt ocurterst by percent, clay content by perccent, or~nic matter by peroent, soil structure by class (very fine granular to blocky or massive) aryl soil permeability by class (rapid to very slow). Parameter aociu:acy was detp*~+++i*+~ fxrmt duplicate lab analyses and expressed as a ~**p*+*?ge to dPtP_im;*+P K sensitivity (Table 4). Since the USIE is associative, a change in R of 0.03 could ~9e calculated soil lass by 0.7 tons/acre. The sensitivity of the USIE to K justifies using K values ril-~hainpri fiYBn on site sampling. Slone Ies~ath Factor (IS) The slope length factor was ~~'~r+++i*+~ by the ctand_~r*r procedure outlined for the USIE (W~~++~~er and Smith, 1978). Slope was measured by repeated Cl~*+~+a*~r sightirgs aryl Slope length was ~++P~~+~~ by chain. Uniform slopes were selected for all sampli~ plots to avoid developing LS factors for irregular slopes. The LS factors were either read directly frrIlR or iSrterpOlated frcmm the USIE Harx~ook (Wig-~,nwier and Smith, 1978). Accuracy was very good for slope lp ~**h. Slope estimates were fx~n repeated observations and also considered aoan-ate. The sensitivity of calculated soil lass to changes in IS was not e~r~*+~. The effect of slope length on annual runoff per unit area is negligible r (W;~~„~w;er arri Stoith, 1978). However, the loll loss per unit area increarsas as slope length increases. The greater aoczmulation of runoff on the longer slopes increases the detachment and transport capacities. Soil loss increases much more rapidly than runoff as slopes steepen (Wisclmieier and Smith, 1978). Slope gradient is directly related to soil detachment and transport capacities. The IS factor is one of the most imTnnr+w„t factors in the USIE, because it aocoimts for