Relationships between soil buffer capacity and selected soil properties in a resource-poor farming area in the Mpumalanga Province of South Africa

Abstract

In this study, the soil buffer capacity (soil BC) was measured for 80 topsoil samples of the most dominant soil forms in a small-scale farming area. Soils used in the study ranged from weakly to strongly buffered, with soil BC values ranging from 0.12 to 2.23 cmol (+) kg-1 pH unit-1. Relationships of soil BC over limited pH ranges showed that at soil BC(pH<4.5) the main buffering mechanism was extractable Al > organic C > clay. At soil BC(pH4.5-6.5) the buffering mechanism was extractable Al > clay > CBD-Al > organic C > CBD-Fe. The main buffering mechanism between pH 6.5-8.5 was clay > CBD-Fe, organic C > CBD-Al. At the general pH range of buffering (4.5-8.5), clay > organic C > extractable Al > CBD-Al > CBD-Fe were the main buffering mechanisms. The main soil forms, viz., Clovelly and Hutton, tended towards lower soil BC, extractable Al (or acidity) and acid saturation, and higher pH, extractable Ca and Mg values, compared to the Magwa and Inanda soil forms which had higher soil BC but lower extractable Al (or acidity), pH and extractable Ca and Mg levels. Clovelly soils tended to have lower clay, CBD-Fe and CBD-Mn contents than the Hutton soils in the study area.