LONG-TERM EFFECTS OF LAND CLEARING METHODS, TILLAGE SYSTEMS AND CROPPING SYSTEMS ON SURFACE SOIL PROPERTIES OF A TROPICAL ALFISOL IN SW NIGERIA

The long-term effects of land clearing methods (manual, shear blade, t ree-pusher/root-rake combination, traditional), tillage systems (disc ploughing, mechanized no-tillage, traditional) and cropping systems (a nnual cropping, alley cropping, grazed pasture) on surface soil physic al and chemical properties were evaluated on an Alfisol in south-weste rn Nigeria ten years after land clearing. Long term soil physical degr adation was greatest after mechanized land clearing or tillage systems . The erosion resulting from soil compaction with mechanized land mana gement systems resulted in exposure of subsoil. Cropping system had no significant effect on soil physical properties. Alley cropping decrea sed exchangeable calcium and pH, and increased total acidity mainly th rough the greater demand for calcium by the hedgerow species. Grazed p asture depleted exchangeable potassium because it was taken up by the grass and exported from the site by the cattle following consumption o f the grass.