Predicting interrill erodibility factor from measured infiltration rate

Direct measurement of an interrill erodibility factor (K-i) is costly and time intensive. As K-i and the final infiltration rate (FIR) under seal formation are both affected by aggregate breakdown at the soil surface, it was hypothesized that the K-i and FIR values are correlative. FIR and soil-loss values of 53 soils, measured in several different laboratory rainfall simulators, were investigated. The slope factor (S-f) of smectitic soils was higher than that of nonsmectitic soils at slope angle (theta) > 9%. The equation S-f = exp (-0.68 + 8.28 sin theta) defines significantly (r(2) = 0.94) the S-f for smectitic soil. For the various soils the FIR and K-i values were correlative and fitted significantly the K-i = a - b In(FIR) model; a and b are empirical coefficients. This model was found applicable for a wide range of rain intensities (34-68 mm h(-1)). However, an increase of the raindrop kinetic energy from <11.6 to 22.3 J mm(-1) m(-2) increased the absolute values of the coefficients, a and b. The FIR-K-i model differed for smectitic and nonsmectitic soils; at a given FIR, the smectitic soils had a higher K-i value than the nonsmectitic soils.