VARIABILITIES OF SOIL CATENA ON DEGRADED IDLLSLOPES OF WATIYA CATCHMENT, WELO, ETlUOPIA

Abstract

The purpose of this study was to establish and explain the characteristics of soil catenas that developed on divergent and convergent hillslopes in the upper Watiya catchment. The two hillslopes have mean gradients of 20 and 16 percent, respectively, and each comprises of a crest, backslope. footslope and toeslope. To accomplish the objectives of the study. a soil pit was opened and described on each hillslope unit. Samples were collected and tested in a laboratory to determine the textural composition and chemical characteristics
of the soils. Soil units were identified on the basis of the revised legend of the Soil Map of the World (FAO/UNESCO, 1990). The crests and backslopes of both hillslope types are severely eroded and marked by shallow soils that meet the requirements for Leptoso]s. The pedon on the convergent footslope with Ap/Bw/Cr horizon sequence was also very much truncated and hence constitutes a severely degraded RapHc Phaeozem. The soils on the convergent toeslope. having typical A/CB/Bb horizon arrangements, were identified as Eutric Regosols. The soil stratigraphic column representing the sequences of modem and
buried soils on this toeslope shows ages that range from about 4000 years before present or upper Holocene to apparently a few hundred years. The oldest buried soil at the base of the stratigraphic column, identified as Eutric Vertisot. is exposed to the surface on the adjacent toeslope of the divergent hillsIope. The unburied Vertisols, which also extend upslope to cover the adjacent footslope of the divergent hillslope have dark brown to very dark grey colour, thick vertical
profile and AI AC or A/C/Cr horizon sequences.