EFFECTS OF SHIFTING AND CONTINUOUS CULTIVATION OF CASSAVA (MANIHOT-ESCULENTA) INTERCROPPED WITH MAIZE (ZEA-MAYS) ON A FOREST ALFISOL IN SOUTH-WESTERN NIGERIA

Soils in farmlands near Ibadan, Nigeria, where shifting or continuous cultivation of cassava intercropped with maize is practised, were sampled in February 1990 and their characteristics compared with those of similar, uncultivated, forest soil. Organic matter, total nitrogen, exchangeable calcium, magnesium, potassium and sodium, cation exchange capacity and pH were lower in the cultivated soils. Continuous cultivation exerted a greater effect on soil organic matter, total nitrogen and available phosphorus status then did shifting cultivation. It is suggested that inorganic and organic fertilizers and mulch should be applied to cultivated soil to conserve the soil nutrients. Fallows of 3-6 years following 1-3 years of cropping appeared incapable alone of adequately restoring soil fertility. They should, therefore, be supplemented with fertilizer applications.