CHARACTERIZATION AND CLASSIFICATION OF SOILS ALONG TOPOSEQUENCE IN ADELE SUBWATERSHED, EAST HARARGHE ZONE, ETHIOPIA

Abstract

Soil characterization and classification is an important tool for identifying the most appropriate use of land as well as for sustainable utilization of the precious soil resources. Field survey and soil laboratory analysis were carried out to characterize selected morphological and physicochemical properties and classify the soils in Adele subwatershed of east Hararghe Zone, Ethiopia. Three representative pedons were opened at three topographic positions (upper, middle, and lower), described in the field and sampled. A total of 24 soil samples 12 disturbed and 12 undisturbed were taken from identified genetic horizons for laboratory analysis. Almost all the pedons were deep (>150 cm) and the soils showed moderately alkaline reaction (pH 7.50-7.96).The soils were low (1.63%) to medium (3.00%) in organic carbon content and very low (0.58 mg kg-1) to low (6.07 mg kg-1) in available phosphorus. The values of cation exchange capacity (CEC) and base saturation ranged from low (15.0) to high (33.2 cmolc kg-1), and high (65.18%) to very high (98.6%), respectively. Based on the field survey and soil analytical results, three main reference soil groups namely, Hypereutric Cambisols (Protocalcic, Endoclayic, Humic) at the upper slope position, Endocalcaric Chromic Luvisols (Hypereutric, Humic)) at the middle slope position and Vertic Kastanozems ( Pantoclayic) at the lower slope position, were identified, However, the detected low to very low available P content of the soils could be the major chemical fertility problem in the soils of the study area, so that external application of P seems to be inevitable based on further more site specific investigations.