| Summary: | This study addresses the issue of soil fertility maintenance in relation to crop yield and farm income growth in general in the west African semi-arid tropics. It describes the structural and the input-output characteristics of food crop production and soil fertility management inside a typical village of southern Upper-Volta and then proceeds to infer from cross-section variations the relationships among the existing soil fertility management practices, soil fertility, crop yields, farm income, resource productivities and the average intensity of land utilization. These inferences are used to identify the technical changes as well as the input and output substitutions that characterize the adjustment mechanism of the cropping system vis-a-vis land use intensification. The technical, social and economic factors that explain and constrain the maintenance and the improvement of soil fertility and thereby limit the growth and the development of the cropping system are pointed out together with the types of agricultural research orientations and rural development policy actions that are most needed to effectively and efficiently relax the major constraints. The cropping system has been shown to be composed of five soil-crop management rings, with varying intensities of land utilization, that conceptually surround the household's habitat. Physical measures of soil fertility suggested that the cropping system more or less maintains or improves the chemical fertility of soils on upland but fails to do so on lowland. However, on upland and over the long term, an intensification of cultivation may have some adverse effects on the physical status of the soil and lead to a decline in field capacity. Statistical measures of yields, farm income and resource productivities following the intensity of land use scale suggested than an increase in the intensity of land utilization caused by an increasing demand for arable lands has no adverse effect on crop yields, farm income and resource productivities. This is made possible by the adjustment mechanism of the cropping system vis-a-vis land use intensification. The main feature of the adjustment process is besides out-migration, a substitution of red sorghum for millet and white sorghum, accompanied by a substitution of mineral and organic fertilizers for fallow.
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