ERODIBILITY OF AGRICULTURAL SOILS IN THE SEMIARID MEDITERRANEAN AREA OF SPAIN

Erosion mapping is a useful tool for soil conservation planning. The p ossible correlation between soil type or lithology with soil erodibili ty has been tested with the aim of facilitating the accomplishment of erosion maps from soil or lithology maps. Soil erodibility (K factor o f the universal soil loss equation [USLE]) was determined from 340 sam ples taken from 4 soil types, on which approximately 95% of agricultur e in the semiarid Mediterranean area is located. Calcaric regosols (K = 0.47) showed the highest erodibility and are significantly different from the other soil types. It was also possible to differentiate betw een calcic xerosols (K = 0.41) and petrocalcic xerosols (K = 0.37). No significant differences were established between the other soil types . The statistical analysis of the soil samples, grouped according to l ithology, showed a better discrimination than is evident from those gr ouped as a function of soil type. It was possible to establish signifi cant differences among all lithologies with the exception of alluvial (K = 0.38) and colluvial (K = 0.38) sediments, which showed a 30% prob ability that the mean values of K were equal. Marls (K = 0.46) were th e most erodible materials. Variance analysis, taking into consideratio n both soil type and lithology, did not improve the discrimination. Th e results from this study suggest that lithological maps may be used f or delineating zones with different erodibility.