Journal of Environmental Management (1991) 32, 105-113 Sustaining Tree Crop Production Under Intensive Land Use: an Investigation into Soil Quality Differentiation Under Varying Cropping Patterns in Western Nigeria O. Ekanade, F. A. Adesina Department of Geography, Obafemi Awolowo University, Ile-Ife, Nigeria and N. E. Egbe Cocoa Research Institute, P.M.B. 5244, Ibadan, Nigeria Received 19 June 1989 Declining soil productivity is a major constraint to crop production in the humid tropics. This paper examines the efficiency of multiple cropping as an economic and biological method of sustaining tree crop productivity in western Nigeria. Soil characteristics under different crops and crop combinations were examined. In addition, soils under a forest in the same locality were considered as an illustration of soil quality in a condition of little or no human interference. The results show the forest unit to be the best in terms of soil quality, followed by cocoa/kola, plantain, kola, and cocoa units in that order. It is suggested that suitable combinations of tree crops can make for higher soil quality. In particular, the combination of plantain with cocoa may help to raise nutrient status, which is usually low under the latter. Keywords: cocoa, plantain, kola, soil productivity, crop production, species diversity, soil quality rating. 1. Introduction A major concern in crop production in most parts of Africa has always been that of sustaining the productivity of the soil. In a recent extensive review of soil management practices and advances in the sub-Saharan region of Africa, Lal (1987) noted the significance of soil factors in the declining trend in crop production in the region. He observed that efficient management of soil resources is crucial to intensifying agriculture and improving production in Africa. Adesina (1989), in the same vein, has noted that little improvement in production of crops can be expected until appropriate soil management techniques are developed and applied in the various parts of the tropics. This observation has been expressed implicitly in some of the earlier works on soil resources of Africa (d'Hoore, 1968; Moss, 1968; inter alia). The effect of poor soil 105 0301-4797/91/020105+09 $03.00/0 9 1991 Academic Press Limited