Effects of rock fragment cover on soil infiltration, interrill runoff and erosion

Considerable attention has been paid recently to the influence of surface r ock fragments on hydrological and erosional processes, although much of thi s research has been done on disturbed soils under laboratory conditions. I have studied the effects of rock fragments on soil infiltration, runoff and erosion under field conditions using simulated rainfall on bare areas of n atural soils within typical Mediterranean scrubland characterized by patchi ly distributed vegetation. Sample areas were chosen where rock fragments co ver more than half the surface within unvegetated patches. Twenty experimen ts were carried out by applying rain at an intensity of 55 mm h(-1) for 60 minutes. This approach shows that rock fragments (i) retard pending and sur face runoff, and (ii) give greater steady-state infiltration rates and smal ler interrill runoff discharges, sediment concentrations and interrill eros ion rates. A second set of six experiments was carried out by applying rain fall at an intensity of 55 mm h(-1) for two runs of 60 minutes. The second run was initiated 10 minutes after the first. During this interval, surface rock fragments were removed in order to measure their effects on infiltrat ion, interrill runoff and erosion rates. In this way, I showed that water a nd soil losses are reduced by the rock fragments. After the removal of rock fragments the steady-state infiltration rate diminished from 44.5 to 27.5 mm h(-1) and the runoff coefficient, sediment concentration and erosion rat es were, respectively, 3, 33 and 39 times greater than they were before the rock fragments were removed.