Impact of soil erosion on the physicochemical properties and productivity of the soil in Wanale Sub-county, Mbale District
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It is estimated that worldwide about 80% of the current degradation on agricultural land is caused by soil erosion and in Uganda, 66 of the 112 districts are exposed to an overall mean erosion risk rate >1 tha−1y−1. Soil erosion deteriorates chemical properties of soil by loss of organic and minerals containing plant nutrients that are necessary for life support system of soil resource as it brings changes in physical properties. As a result, more and more soil erosion studies in Uganda are carried out in order to get better understanding about why the phenomenon happens and what could be done to solve the problems but the studies have not focused on comparing the physio-chemical soil properties and crop yields obtained from soil erosion affected gardens and those that have no soil erosion history. Therefore a study was conducted in Wanale Sub-county to investigate the effect of soil erosion on the chemical and physical properties of soil at different landscape positions in Wanale and to assess the effect of soil erosion on crop yields so as to enable farmers and policy makers to make informed predictions on the future productivity of the soils and required agricultural inputs and suitable land management practices to replenish the lost productivity of affected soils. In the study, soil samples were collected from eight sampling gardens at 4 different points in atop sequence (Top, Middle, base, and valley) along a hill in Buwasu village, Wanale sub-county and taken to the soil science laboratory in the school of agricultural sciences, Makerere University for subsequent processing and analysis. It was observed that soil erosion significantly impacted the soil pH and depth while the concentration of macro nutrients (Total Nitrogen, Potassium, Calcium) and Organic carbon in gardens affected by soil erosion were not significantly different from the concentration in soil samples from gardens without history of soil erosion but were lower than their respective required critical levels in the soil. And when analyzed with topography, Organic carbon and Nitrogen percentages showed significant differences between the middle block and all other blocks. Poor crop yields were also recorded in gardens without erosion history and they did not significantly differ from those obtained from erosion affected sites and this was attributed to continuous nutrient mining in gardens without history of erosion by agricultural activities. Nutrient replenishment strategies into the soil should therefore focus on both erosion affected and those gardens not affected by soil erosion as the study concluded that both areas are deficient of macro nutrients necessary for plant growth.