A rapid method for assessing sodicity hazard using a cation exchange membrane

Ion exchange reactions which occur between the soil and synthetic resin surfaces have been used to approximate nutrient movement and uptake by plants. Similar exchange principles govern the proportion of sodium which will exist on the soil exchange. This study investigated the use of a cation exchange membrane (CEM) in estimating the sodicity of soil. For soils ranging in salinity from non to extremely saline, the saturated paste extractable sodium was not well related to the CEM exchangeable amounts. However, the sodium adsorption ratio (SAR) was closely related to the CEM exchangeable Na (r² = 0.95), suggesting a link between Na on the soil exchange complex and that adsorbed by the CEM. The factors which control the ion exchange dynamics of the soil exchange complex appear to similarly control cation exchange onto the CEM. This premise was used as the basis for a simplified measure of exchangeable sodium percentage (ESP). Sodium occupying the CEM, expressed as a percentage of the entire CEM capacity, showed a one to one correspondence with ESP measured using standard methods (r² = 0.91). Exchange membranes, therefore, offer a simple and rapid method of assessing soil sodicity.