Re-use of industrial and agricultural wastewater for irrigation can increase the concentration of potassium in
soil and affect soil structure. However, investigations of clay dispersion have traditionally focused on soils with high exchangeable sodium, therefore exchangeable sodium percentage (ESP) has been used to assess soil structural stability. Currently, Australian soils have been considered non-sodic or non-dispersive when the soil ESP <6. However, a few studies have demonstrated that potassium (K) ions in the exchange complex of soil can also assist clay dispersion even when the exchangeable sodium (Na) levels are minimal.
The dispersion (as turbidity) and ESP were measured on 74 Australian soils. 17 of those soils showed a considerable level of dispersion, despite ESP <4.5. In all of these soils the Na to K ratio was <1. The relationships between ESP and turbidity were poor (R2= 0.23) indicating limitations of using the ESP for identifying potentially dispersive soils when K is present on the soil exchange sites. Therefore, we used exchangeable cation ratio (ECR), as an index alternative to ESP, but which takes into account effects of exchangeable K on clay dispersion. The good correlation obtained between ECR and the parameters like turbidity and zeta potential support its use in assessing soil structural stability when the appreciable amount of K present on exchange sites
