Refining the interpretation of orthic horizons in South Africa

The relationship between soil water regime and soil profile morphology could contribute towards improving catchment water yield. This paper proposes refinements to the interpretation of orthic A horizons ( ochric ), defined in Soil Classification — A Taxonomic System for South Africa, to aid interpretation for hydrological purposes. Soil water contents have been measured for six years in the Weatherley catchment in South Africa and used to classify orthic A horizons in terms of wetness classes defined in the Soil Survey Manual. The well drained class is applicable to orthic A horizons overlying red apedal B, yellow-brown apedal B ( agric or ferralic ) or neocutanic B ( cambic ) horizons. The moderate poorly and poorly drained classes are applicable to orthic A horizons overlying E ( albic ), soft plinthic B ( ferric ) or G ( gleyic ) horizons. The occurrence of mottles and matrix colour can be used for differentiation between the latter two wetness classes. Interpretation of orthic A horizons can therefore be enhanced by wetness classification, utilizing the nature of the underlying horizon, the occurrence of mottles and matrix colour.