Assessing the magnitude of land use/cover changes and their effect on soil properties in the transboundary River Sio catchment (Uganda/Kenya border)

Abstract

The multiplicity of land uses in affecting the quality of physical and chemical properties of soils and reducing natural vegetation cover is of a growing concern in Uganda today. Consequently, the study investigated the effects of land use/cover change on soil properties in River Sio catchment. Specifically, the study intended; to determine the magnitude of land use/cover change, examine the main drivers of the change and assess their effects on the soil properties. The magnitude of land use/cover was determined by an application of unsupervised image classification procedure on the Ortho-rectified Landsat TM/ETM images of 1986 and 2000 using ILWIS 3.3 software. Two hundred questionnaires were administered to the randomly selected local residents and 10 purposively selected key informants. These were analyzed using a Binary Logistic Regression in SPSS windows program version 10.0 to determine the main drivers of change. To assess the effects of land use/cover change on soil properties, cultivated land (maize, sugarcane & cassava) converted from grasslands were selected at different landscape positions. Composite soil samples were randomly collected from each location and land-use type, including grasslands, totaling to 272 samples taken at two soil depths (0-15cm & 15-30cm) for comparisons. The results showed that; in the period of 1986 and 2000, wetlands and bushlands largely reduced by 21% and 5% respectively while small scale farming and grasslands increased by 14% and 12% respectively. The main drivers of land use/cover change were household size and customary landownership. Other drivers included; shift from perennial to annual crops, weak catchment laws, decline in soil fertility, increased livestock activities, use of fire in land management and shorter distances covered to cultivable farmlands. The conversion of grasslands into cultivated land affected negatively the amounts of available nitrogen content in the topsoil (0-15cm) and subsoil (15-30cm), and also on organic matter, phosphorous content in the same subsoil at both the mid and downstream sections of Sio catchment.