Classifying the sensitivity of soils of the South African highveld to acidification

Abstract

The potentially acidifying impact of air pollution coupled with agriculture and forestry has stimulated interest in the spatial assessment of soil quality deterioration in the highveld and eastern escarpment region of South Africa. Current information on soils is available as 1:250 000-scale land type maps depicting areas of relatively uniform soil pattern for which there is a quantitative inventory of soil series distribution. The objective of this study was to convert this information into a regional map showing the sensitivity of soils to acidification. Topsoils from 143 modal profiles, representing 57 soil series of the binomial classification system, were analysed for acid neutralizing capacity (ANC) using a simple method of pH measurement in acetate buffer solution. The relationship between ANC and relevant textural and chemical properties was then employed to classify, directly or by pedogenic inference, all the 504 series in the binomial system into 4 sensitivity categories. Arclnfo geographic information system (GIS) software was them employed to depict land types, classified in terms of their content of acid-sensitive soils, in a way which allows the most sensitive areas of the highveld to be identified as a basis for facilitating research and land use planning activities. The system for classifying soils in terms of acid sensitivity can be applied to any area in South Africa for which land type maps are available.