Relationship between cation exchange capacity, clay content and water retention of Highveld soils

Abstract

Water in the soil is held by capillary and adsorption forces. These forces are mainly a function of clay content and mineralogy. To neglect the influence of clay mineralogy when estimating the water-holding properties of soil, implies that only a part of these forces is considered. It is convenient to use some easily measurable soil property to quantify the effect of clay mineralogy, In this study cation exchange capacity (CEC) was used for this purpose. For 320 soil samples of the Highveld Region, water content at a matrix potential of - 33 kPa, −1 500 kPa and the percentage water retained between −33 kPa and - 1500 kPa (ΔW), were compared with different parameters. The water retentivity of disturbed soils can be predicted more accurately if variations in CEC are taken into account. Highly significant multiple correlation coefficients of 0, 97, 0, 96 and 0, 91 respectively, were calculated for the relationships of CEC (me/100 g soil) and clay content with water content at −33 kPa and - 1 500 kPa and with ΔW.