Relationship between acid saturation and hydrogen activity of soils from different districts in South Africa

Abstract

Soil analyses results from six districts in the western maize producing areas of South Africa were used for correlating exchangeable acidity and acid saturation with hydrogen ion activity (pH). From the resulting regression equations, the pH values that corresponded with an acid saturation of 20% were calculated for the different districts. Significant linear correlations were found between acid saturation and hydrogen activity for all districts, but the slopes for the drier western districts were lower than those of the more humid eastern districts. The pH values for an acid saturation of 20% were also lower for the western districts than for the eastern districts. These pH (KCl) values ranged between 4.05 to 4.45. The same trends were found with the correlation between exchangeable acidity and hydrogen activity. This indicates that differential Al solubility is the reason for the different relationships between districts. Mineralogical differences could be responsible for these trends, since Al is more exposed to the soil solution in 1:1 minerals (humid areas) as compared to 2:1 minerals (arid areas).