The relationship between subsoil colour and degree of wetness in a suite of soils in the Grabouw district, Western Cape II. Predicting duration of water saturation and evaluation of colour definitions for colour-defined horizons

Existing colour indices were evaluated to determine their correlation with duration of water saturation, for a hydrosequence in the Grabouw district, Western Cape. Correlation coefficients ranged between 0.31 and 0.63. More simple colour indices were developed. Dry soil colour is a relatively good indicator (r = 0.77) of duration of free water. For this study the equation: Duration of free water = 2.35 x Huedry + 5.79 x Valuedry − 7.31 Chromadry – 27.89 can be used to predict duration of free water in diagnostic red apedal B, yellow-brown apedal B, yellow E and grey E horizons. It seems that the present colour definitions for diagnostic horizons in the South African soil classification system are sufficiently accurate to distinguish meaningfully between these horizons with respect to duration of free water.