Effects of land use change on soil qualities in Sasumua catchment
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Sustainability of natural resource base is dependent on good land management. Land use change from forest to agricultural land can endanger sustainability of soil productivity if not well managed. Effects of land use change from forest to annual crop cultivation and grazing on soil qualities were investigated in Sasumua catchment with the aim of (a) determining the changes in selected physical and chemical qualities (b) establishing how various soil quality indicators vary with different land management practices and (c) developing the minimum data set for determination of soil health. A survey of farms and forest was carried out by collecting soil and water samples from randomly selected sites. Measurement of CEC, exchangeable Ca, Mg, K and Na, pH, EC, base saturation, total N, soil carbon and texture, bulk density and hydraulic conductivity was done on soil samples while water samples were analyzed for quality. Effects of land management practices were determined using structured questionnaire. The long term effects of cultivation of land after land use change from forest was determined by comparing the levels of selected soil qualities over a 30 years period. These results were then subjected to factor analysis using principal component analysis to determine the appropriate indicators by developing the minimum data set. The results shows significant change of soil pH and silt content when land is converted from forest to grazing land and annual crops cultivation. In grazing land ; CEC , exchangeable Ca2+ and Mg2+, base saturation and sac decreased by 8%, 42%, 52%, 32% and 8% respectively while Total N increased by 6 % . In annual crop cultivated land; exchangeable Ca2+and Mg2+, base saturation and sac decreased by 31% ,40% ,32% and 8% respectively, while CEC, Total N, and bulk density increased by 14%, 23% and 10% respectively. Land management practices such as intensive cultivation of horticultural crops, overgrazing of pastureland and farming on steep areas were contributing to soil chemical and physical degradation while addition of farmyard manure and agro forestry were contributing to sustainability of soil organic carbon and bulk density. Tillage in cultivated fields influenced increase in CEC. Water quality results indicated that land use management affected quality as it flows from forest to areas with human settlements. It was found that there is a decline of soil quality over the 30 year period. This soil quality decline from 1977 to 2007 is related to the increase in the area population from 9 to 260 persons per square kilometer over the same period. Soil pH, texture, sac and CEC were found to be the best indicators of soil health In the catchment.