Effects of land cover changes and slope gradient on soil quality in the Gumara watershed, Lake Tana basin of North-West Ethiopia

This study evaluated land cover change and slope gradient on selected soil quality parameters in the Gumara watershed, northwestern Ethiopia. 36 soil samples were collected from 0- to 20-cm depth under four land cover types across three slope gradients. The collected soil samples were analyzed for selected soil quality parameters. Result indicated that the bulk density of the soil is different (P < 0.001) in the watershed because of land cover change and slope gradient. Cultivated land and steeper slopes have the highest bulk density and lowest total porosity. On the other hand, the forestland and gentler slopes have lowest bulk density and high total porosity. Intensive cultivation accompanied by continuous conversion of forestland to cultivated land caused high bulk density and low total porosity. Cation exchange capacity, exchangeable magnesium total nitrogen, available phosphorus and potassium negatively correlated with slope gradient. Conversion of forestland to cultivated land contributed to changes in pH (P < 0.05) exchangeable calcium (P < 0.01), potassium (P < 0.001), available phosphorus (P < 0.01) and nitrogen (P < 0.01) content. The soil degradation index results showed that soil organic carbon, nitrogen, available phosphorus and exchangeable potassium contents declined and bulk density increased because of the land cover change. This negative effect on agricultural development and environmental health of the watershed makes an integrated land resource management approach vital for sustaining agricultural productivity and the environment health of the Gumara watershed.