PROCESSES OF SOIL MOVEMENT ON STEEP CULTIVATED HILL SLOPES IN THE VENEZUELAN ANDES

Erosion from cultivated lands continues to threaten the sustainability of commercial and subsistence agriculture around the world. Although most erosion is attributed to rainfall-induced runoff, other processes were observed which may account for a large portion of soil movement on sloping farm lands. Soil movement was measured on 15 parcels cultiv ated by subsistence farmers in the Venezuelan Andes as part of a broad er study on adoption of soil conservation practices. Sediment traps we re installed at the outlet of fields with slopes ranging from 33% to 7 8%. Based on the type of material found in the traps-clods, stones and some consolidated earth-soil movement was attributed to plowing, weed ing, concentrated flows entering the field from above and, to a lesser extent, rainfall. Soil flux ranged from 1.5 to 58.7 kg m(-1) yr(-1) w ith an average of 31.1 kg m(-1) yr(-1). Three parcels underwent low fl ux, 1.5 to 5.7 kg m(-1) yr(-1) and 12 showed a higher flux, 16.7 to 58 .7 kg m(-1) yr(-1). This study served to identify a number of soil ero sion mechanisms not often considered when designing soil conservation programs targeted for areas with steep slopes. Tillage translocation a nd weeding within parcels contributed considerably more to soil and st one movement than did rainfall. The findings suggest that, when design ing soil conservation programs for such areas, emphasis should be plac ed on methods devised to minimize soil disturbance. Among the practice s that may be promoted are minimum or zero-tillage, the use of ground covers to control weeds and the installation of stone or grass barrier s to retard the downward movement of soil. (C) 1997 Elsevier Science B .V.