Effects of topography and land use on soil characteristics along the toposequence of Ele watershed in Southern Ethiopia

Information on soil properties and distribution is critical for making decisions with regard to crop production and mitigating land degradations. A reasonable way of deriving the information is using proxy environmental characteristics that have demonstrated relationships with soil properties. A field study was conducted to evaluate the relationship between topography, land use and soil properties. Three slope classes were considered and a total of three pedons, one on each slope class, were opened and described at the Ele watershed in southern Ethiopia. Soil samples collected from identified horizons of each pedon were analyzed for physicochemical properties. Additionally, random soil samples were collected from adjacent cultivated, grassland and forest soils; and three composites were made for each land use type within the three slope classes. All three pedons showed remarkable variability in physical, chemical, and morphological characteristics of the soils. The field as well as laboratory textural class determinations revealed the dominance of clay fraction in the soils. The existence of buried horizons with abrupt textural as well as sharp changes in color both in dry and in moist showed the occurrence of lithological discontinuity. Both soil pH and EC were low for steep slope and highest for the middle slope class, whereas the organic carbon (OC), total N (TN) and available P decreased down the slope. Gentle and moderate slope classes had the highest exchangeable bases, while the steep slope had the lowest owing to the removal and deposition of exchangeable bases by water erosion. The chemical properties of the soils were also significantly affected by land use. The highest values of both pH and EC were obtained in cultivated land, whereas grassland had relatively more OC, exchangeable Ca, Mg, K and available micronutrients than the other land use types.