Effects of rock fragments cover and slope on infiltration, runoff and soil loss in an entisol

Abstract

In order to evaluate the effects of rocks fragments and slope classes on infiltration, runoff and soil loss processes, an Entisol was selected in the ‘Sector Cucurucho’ at the Tovar municipality in Aragua State, Venezuela, with a high prevalence of particles (silt + very fine sand + fine sand) that reflects a low stability to the impact of the drops. However it shows a high stability to wetting, with the proportion of rock fragments (by weight and by volume) highly variable. The slope and rock fragment cover classes for this study were selected through a frequency analysis resulting from the determination of slope gradients and surface stoniness, using a clinometers and a 10x10 mesh, respectively. The slope classes were: <24, 24 - 36, 36-48 and > 48%, while surface stoniness classes selected were: <14, 14 - 28, 28 - 42 and > 42%. Infiltration rate, surface runoff and soil loss in each slope class and rock fragment cover class were evaluated in plots (20 x 30 cm) using a portable rainfall simulator applying rainfall intensities of about 100 mm h-1 during one hour. The effect of slope gradient was highly significant for runoff and soil loss, but not significant for infiltration rate, even though there was a slight tendency to decrease with slopes greater than 48%. The effect of rock fragment was not significant on infiltration rate, runoff and soil loss, which can be attributed to the variable rate of rock fragments within the soil volume. We found a positive association between runoff and soil loss (R = 0,857 **), while the infiltration rate showed a negative association with runoff (R = -0,562 **) and soil loss (R = - 0,445 *).