The relationship between subsoil colour and degree of wetness in a suite of soils in the Grabouw district, Western Cape I. Characterization of colour-defined horizons

Abstract

Soil colour is an easily identifiable property that is invariably used as a parameter in all soil classification systems including the system used in South Africa. To test the hypothesis that soil colour is a reflection of the soil water regime, the physical, chemical, morphological and hydrological properties were measured for soils on three catenas in the Grabouw district, Western Cape. Significant differences were observed between diagnostic red apedal B, yellow-brown apedal B, yellow E and grey E horizons. Fine silt, silt, clay, sum of cations, cation exchange capacity and free iron and aluminium decreased in the sequence red apedal B > yellow-brown apedal B > yellow E > grey E horizons. Average duration of free water saturation was 1.3% for red apedal B horizons, 18.8% for yellow-brown apedal B horizons, 42.4% for yellow E and 54.2% for grey E horizons. This supports the hypothesis that yellow and grey horizons are formed by a process of reduction and leaching.