SOIL CHARACTERIZATION, CLASSIFICATION AND QUALITY ASSESSMENT IN KERSA SUB-WATERSHED, EASTERN ETHIOPIA

Abstract

Knowledge about types of soils and the status of their quality is needed for developing sound land use planning and soil management decision for enhancing crop productivity. However, such information is lacking in Kersa sub-watershed in eastern Ethiopia where the current study was conducted. The objectives of this study were, therefore, to 1) characterize and classify soils of the study area, 2) determine soil quality indicators using minimum data set and calculate soil quality index for different land uses, and 3) evaluate soil organic carbon (SOC) stock under different land use types and soil depth in three adjacent land use types (cultivated, grazing, and fallow lands) in Kersa sub-watershed, eastern Ethiopia. Eight representative pedons were opened at three topographic positions (upper, middle, and lower) for the characterization and classification study. For the soil quality evaluation, soil samples were collected from the surface (0-20 cm) layers from each land use in triplicate. Soil samples were collected from three depths (0-20, 20-40, and 40-60 cm) of the three land uses for SOC stock assessment (SOCS). Topography played a dominant role in the formation of soils in the study area. In general, soils in the upper topographc positions are shallower and inferior in most of the measured soil attributes, while those in the lower topographic positions are deeper and superior in the measured properties. Following the World Reference Base legend, five Reference Soil Groups were identified: Gleyic Vertic Luvisols (Clayic, Cutanic) and Happlic Vertisols (Mollic)in the lower topographic position, Hypereutric Cambisols (Loamic) in the middle topographic position, and Hypereutric Leptosols (Loamic) and Hypereutric Endoleptic Regosols (Loamic)in the upper topographic position. The soil quality analysis results revealed that the grazing land has the highest soil quality index (0.69) followed by cultivated (0.62) and fallow (0.59) lands although all of these values fall under intermediate soil quality (0.55 < SQI < 0.70) class. Available phosphorus, bulk density, aggregate stability, pH, CEC, and soil organic carbon content were found to be the major quality indicators among the three land uses. The soil organic carbon stock assessment study also indicated the presence of significant (P ≤ 0.05) difference in carbon stock of the three land use types. Soil under grazing land use type had significantly higher values of SOCS (42.9 t/ha and 32.9 t/ha) than cultivated (32.6 t/ha and 26.3 t/ha) and fallow (23 t/ha and 12.5 t/ha) land use types xvi in their surface and subsurface layers, respectively. Therefore, based on the present findings enhancing soil organic matter, using soils according to their potential and periodic evaluation of soil quality are recommended to ensure enhanced agricultural productivity on a sustainable basis.