A RAPID METHOD FOR ASSESSING SODICITY HAZARD USING A CATION-EXCHANGE MEMBRANE

Ion exchange reactions which occur between the soil and synthetic resi n 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 us e of a cation exchange membrane (CEM) in estimating the sodicity of so il. For soils ranging in salinity from non to extremely saline, the sa turated paste extractable sodium was not well related to the CEM excha nge able amounts. However, the sodium adsorption ratio (SAR) was close ly related to the CEM exchange able Na (r(2) = 0.95), suggesting a lin k between Na on the soil exchange complex and that adsorbed by the GEM . The factors which control the ion exchange dynamics of the soil exch ange complex appear to similarly control cation exchange onto the GEM. This premise was used as the basis for a simplified measure of exchan geable sodium percentage (ESP). Sodium occupying the GEM, expressed as a percentage of the entire CEM capacity, showed a one to one correspo ndence with ESP measured using standard methods (r(2) = 0.91). Exchang e membranes, therefore, offer a simple and rapid method of assessing s oil sodicity.