ASSESSMENT OF SOIL PHYSICOCHEMICAL PROPERTIES ALONG THE TOPOSEQUENCE AT RUKETI COMMUNITY WATERSHED, SODO DISTRICT, GURAGE ZONE, SOUTHERN ETHIOPIA

Abstract

Variations in slope positions can influence the physical and chemical properties of soils depending on the soil’s position in the local topography. Topographic factors in turn affect soil processes and the distribution of soil in a given land use system. Therefore, a studying on the effect of slope positions and soil depths on selected soil properties is of paramount importance inRuketi community watershed, Sodo district. The general objective of this study was, therefore, to assess the soil physicochemical properties along the toposequence of Ruketi communitywatershed, Sodo district. The study area was divided into four slope positions (summit, shoulder, back, and toe slope positions) and two soil depths (0-20 and 20-40 cm). A total of twenty-four (24) composite disturbed and undisturbed soil samples were collected from the two soil depths for analysis of pertinent soil properties and analyzed in the laboratory using standard procedures. Results indicated that most of the physicochemical properties showed relative variations in response to slope positions and soil depths. The textural class of soils ranged from loam to clay loam. A higher bulk density value (1.53 g cm-3) was recorded in the subsurface soils. Total porosity ranged from 44.59 to 47.86 % with the highest (47.86 %) at the back slope position. The pH values increased with soil depth and ranged from 5.89 to 7.35. The highest CEC (33.83 cmol (+) kg-1) was recorded followed by (31.95 cmol (+) kg-1) at toe and back slope positions, respectively. The highest exchangeable bases (Ca, Mg, K, and Na) were recorded relatively at the lower slope positions at both soil depths. Exchangeable Ca and Mg were the predominant captions in the exchange sites of surface and sub-surface soil layers. The highest soil OC content (2.47%) and lowest (1.26%) were recorded at the shoulder and back slope positions, respectively, and soil OC content decreased with increasing soil depth. The total nitrogen content ranged from 0.11 to 0.21% following the same trend with soil OC across soil depths. The highest available phosphorus (6.35 mg kg-1) was recorded at toe slope positions and the value ranged from 3.82 to 6.35 mg kg-1in soils of the summit and toe slope positions. The values of exchangeable bases and base saturation were varied across slope positions and higher at toe slope positions. In general, the results indicate that most of the soil properties were lower in soils at in all slope positions of the two soil depths suggesting that soil fertility management needs to be implemented to improve agriculture productivity sustainably in the watershed.