Estimation of soil water retention from clay content and cation exchange capacity values of soils

Soil water characteristics can be estimated accurately from the clay content and cation exchange capacity (CEC) values of soils. The clay with its very large adsorption surface and CEC which reflects the negative charge of clays, is jointly responsible for adsorbing di-polar water molecules. Formulae relating clay content and CEC to soil water content at matric potentials of −33, −80, −500 and −1500 kPa were calculated using the results obtained with the pressure membrane technique on 100 soil samples and then validated with a further 200 soil sample measurements. Clay content and CEC accounted for more than 93% of the variability in soil water at the four measurement points.