Abstract
Changes in the permeability and the swelling of a montmorillonite-rich soil were measured for a range of sodium adsorption ratio (SAR) and electric conductivity (EC) values of the leachant. Concentrations, related to a 20% drop in hydraulic conductivity (HC) and the start of a rapid swelling process, were between 40 and 400 meq/liter, and were called "threshold" and "jump-off" concentrations, respectively. The initial leaching of the soil cores with highly saline solutions gave high HC values for the leachants with high SAR's, and low HC values for the leachants with low SAR's. Subsequent tests with diluted solutions reversed the situation; solutions with high SAR's lowered the HC of the soil drastically to HC values well below those of the soil cores treated with low SAR leachants. Solutions with a low EC or a high SAR, or both, maintained in their leachates EC and SAR values above and below, respectively, the expected equilibrium values. Increased solubility of the 40.6 t/ha of gypsum accounted for the discrepancy.
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