Exchangeable Cation Hydrolysis and Soil Weathering as Affected by Exchangeable Sodium

The specific conductance and chemical composition of aqueous soil suspensions were measured as a function of time on suspensions prepared from three arid soils pretreated with acidified salt solutions to remove lime. The release of Ca 2+ , Mg 2+ , and K + from silicate minerals and the hydrolysis of exchangeable Na + occurred rapidly and prevented the preparation of homoionic Na soils. Crystalline ion release and hydrolysis of exchangeable Na + and Ca 2+ continued after the soils were suspended in distilled water. The rate was enhanced by increasing exchangeable NA + . The combination of Ca 2+ hydrolysis and its release from silicate minerals was sufficient, when coupled with Na + hydrolysis, to cause the solution phase of the suspension to be supersaturated with lime for one soil. Separate experiments with untreated soil and its silt fraction indicated that silt weathers rapidly and contributes significantly to the increase in soil conductance. Silt weathering was enhanced by increasing exchangeable Na + .