Impact of land use/cover change and slope gradient on soil organic carbon stock in Anjeni watershed, Northwest Ethiopia

Today's agri-food systems face the triple challenge of addressing food security, adapting to climate change, and reducing the climate footprint by reducing the emission of greenhouse gases (GHG). In agri-food systems, changes in land use and land cover (LULC) could affect soil physicochemical properties, particularly soil organic carbon (SOC) stock. However, the impact varies depending on the physical, social, and economic conditions of a given region or watershed. Given this, a study was conducted to quantify the impact of LULC and slope gradient on SOC stock and C sequestration rate in the Anjeni watershed, which is a highly populated and intensively cultivated area in Northwest Ethiopia. Seventy-two soil samples were collected from 0-15 and 15-30 cm soil depths representing four land use types and three slope gradients. Soil samples were selected systematically to match the historical records (30 years) for SOC stock comparison. Four land use types were quantified using Landsat imagery analysis. As expected, plantation forest had a significantly (p < 0.05) higher SOC (1.94 Mg ha(-1)) than cultivated land (1.38 Mg ha(-1)), and gentle slopes (1-15%) had the highest SOC (1.77 Mg ha(-1)) than steeper slopes (> 30%). However, higher SOC stock (72.03 Mg ha(-1)) and SOC sequestration rate (3.00 Mg ha(-1) year(-1)) were recorded when cultivated land was converted to grassland, while lower SOC stock (8.87 Mg ha(-1)) and sequestration rate (0.77 Mg ha(-1) year(-1)) were recorded when land use changed from cultivation to a plantation forest. The results indicated that LULC changes and slope gradient had a major impact on SOC stock and C sequestration rate over 30 years in a highly populated watershed. It is concluded that in intensively used watersheds, a carefully planned land use that involves the conversion of cultivated land to grassland could lead to an increase in soil C sequestration and contributes to reducing the carbon footprint of agri-food systems.