Towards predicting the soil-specific threshold electrolyte concentration of soil as a reduction in saturated hydraulic conductivity: The role of clay net negative charge

The use of marginal quality water with saline and dispersive properties is set to become more prevalent in agricultural production given demands on freshwater resources. The threshold electrolyte concentration (CTH) is often used to define the suitability of such water, with irrigation practitioners seeking a general predictive model based on soil order. Recent work supports that the CTH absolute value is soil-specific, although there remains a requirement to identify the contribution of predictive factors in an effort to create a predictive function for the CTH. This work used 58 soils to explore the variability of the CTH within and between soil orders, subsequently comparing saturated hydraulic conductivity to leachate turbidity as a means to investigate CTH existing prior to the point of spontaneous dispersion. The role of clay net negative charge was investigated in terms of its relation to the CTH in an effort to move towards a predictive capacity for this soil-specific characteristic. Subsequently, it was demonstrated that the CTH was apparently described by net negative charge of clay particles, suggesting that surface interactions between clay particles and the bulk solution are important in governing soil stability from a soil-specific point of view The CTH occurred prior to the aggregate-dispersion threshold and was clearly soil-specific, even within a soil order. Future work is required to incorporate the ionisation potential and clay domain pressure models of soil stability to move towards a CTH predictive function based on quantified differences in soil mineralogy and charge characteristics, which is discussed.