ASSESSMENT OF SELECTED PHYSICAL AND CHEMICAL PROPERTIES OF SOILS UNDER DIFFERENT LAND USES AND SLOPE POSITIONS AT GOLA WACHU SUB-WATERSHED, EAST HARARGHE ZONE, ETHIOPIA

Understanding the effects of land use types and slope positions on soil physicochemical properties is an essential for sustainable soil management. Therefore, this study was initiated to assess selected physicochemical properties of the soils under different land uses and slope positions at Gola Wachu sub-watershed, east Hararghe Zone, Ethiopia. The study area was divided in to three topographic unit based on slope positions (upper, middle and lower) and selected soil physicochemical properties were characterized under three adjacent land use types: cultivated land (CL, grazing land (GL), fallow land (FL). A total of twenty-seven surface composite soil samples were collected from (0-20 cm) soil depth for the analysis of relevant soil physicochemical properties, following the standard laboratory procedures. All of the analyzed soil physicochemical properties were varied significantly (P < 0.05) among the three land use types, except particle size distribution, C/N and PBS. The textural class of soils under all the land use types at each slope positions are clay loam. Relatively higher bulk density (BD) values (1.33 g/cm3 ) were recorded in soils of under CL of upper slope compared to the other land use types whereas the lower BD (1.19 g/cm3 ) was observed under GL of lower slope. Total porosity varied from 49.80% under CL of upper slope to 55.09% under GL of lower slope. The pH varied (6.92) in grazing land of lower slope to low (5.89) in the soils of cultivated land at upper slope. The EC in dS/m was high (0.068) in grazing land of lower to low (0.02) in cultivated land use of upper slope. The SOM ranged from 1.98% in grazing land of lower slope to 1.15% in cultivated land of upper slope. TN, in % was high (0.18) in GL of lower slope to low (0.12) in CL of upper slope. C/N ratio was high (7.58) in GL of lower slope and low (5.30 in CL of upper slope. CEC in cmol (+)/kg was high in GL of lower slope (52.06) to low (46.04) in CL of upper slope. The exchangeable Ca, Mg, K and Na in cmol (+)/kg were high (21.98, 10.14, 1.17 and 0.92) in GL of lower slope to low (18.23, 7.85, 0.56 and 0.65) in CL of upper slope, respectively. PBS was high (70.72%) in GL of lower slope to low (57.69%) in CL of upper slope. Extractable micronutrients Fe, Mn, Zn and Cu in mg/kg were high (15.48, 22.17, 0.89 and1.37) in GL of lower slopes to low 13.23, 19.07, 0.47and 1.18) in CL of upper slopes, respectively. Most of the physicochemical properties showed relative variations in under different land use types in each slope positions. In general, the results indicate that most of the soil physicochemical properties were lower in soils of the cultivated land at each topographic positions signifying that soil fertility management is required in order to make agriculture sustainable in the Sub-watershed.