EFFECT OF FOREST CLEARANCE AND BURNING ON SOIL PROPERTIES IN NORTHERN RORAIMA, BRAZIL

Clearance of evergreen seasonal forest for cattle pasture is examined in an area of northern Roraima. Coloniao (Panicum maximum Jacq.) and kikuyu grass (Brachiaria humidicola (Rendle) Schweik.) are commonly established on cleared forest land. Current rates of clearance are rather low as also is grazing intensity (1-2 animals ha-1), but soil physical and chemical changes are occurring. Thus, topsoil bulk density increases over time in new pastures. Also, available nutrients decline from the enhanced levels that prevail after initial clearance and burning. In particular, available P is low in the acid soils and, as elsewhere in Amaonia, probably limiting to pasture growth. For local ranchers, the best source of nutrients is the standing forest, so every incentive exists to continue forest destruction for new pasture.