Soil - water relationships in the Weatherley catchment, South Africa

Soil water content is influenced by soil and terrain factors, but studies on the predictive value of diagnostic horizon type for the degree and duration of wetness seem to be lacking. The aim of this paper is therefore to describe selected hydropedological soil-water relationships for important soils and diagnostic horizons in the Weatherley catchment. Daily soil water content was determined for 3 horizons in 28 profiles of the Weatherley catchment. These data were used to calculate annual duration of water saturation above 0.7 of porosity (ADs>0.7), which was correlated against other soil properties. Significant correlations (α = 0.05) were obtained between average degree of water saturation per profile and slope (R2 = 0.24), coarse sand content (R2 = 0.22), medium sand content (R2 = 0.23), fine silt content (R2 = 0.19), and clay content (R2 = 0.38). ADs>0.7 per diagnostic horizon ranged from 21 to 29 d•yr-1 for the red apedal B, yellow brown apedal B, and neocutanic B horizons; 103 d•yr-1 for the orthic A horizons; and from 239 to 357 d•yr-1 for the soft plinthic B, unspecified material with signs of wetness, E, and G horizons. A regression equation to predict ADs>0.7 from diagnostic horizon type (DH), clay to sand ratio (Cl:Sa), and underlying horizon type (DHu) gave: ADs>0.7 = -26.31 + 41.64 ln(Cl:Sa) + 35.43 DH + 13.73 DHu (R2 = 0.78). Results presented here emphasise the value of soil classification in the prediction of duration of water saturation.Keywords: diagnostic horizon, model, slope, soil texture, water saturatio

Die Keuring van Studenteverpleegkundiges aan die Randse Afrikaanse Universiteit — ’n Oorsig

In student selection for the degree in nursing (B.Cur.) at the Rand Afrikaans University two rating scaies are used consisting of an academic and an interview component. In calculating the academic mark an extra weighting is given to subjects such as Biology, Science and Mathematics and to subjects taken at higher grade. In an overview comparing the selection results of 137 candidates, selected for the degree since 1975, with the examination results of the first year at University it is evident that the academic mark is a reasonably reliable norm in student selection. The value of the interview has not been established and further research and adaptations are necessary

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

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.Articl

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 × Huedry + 5.79 × 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.Articl