The effect of electrolyte solutions on the unsaturated hydraulic conductivity of a sodic clay soil

Abstract

A technique for measuring the effect of different electrolyte solutions on the unsaturated hydraulic conductivity of low permeability soil cores is described. The technique was used to assess the effect of infiltrating gypsum (CaS0,.2H20) solution, sodium chloride solution, and distilled water on the conductivity of a sodic heavy clay at matric potentials between -0.5 and -8 kPa. Percolation of one liquid-filled pore volume of gypsum solution (concentration 29 m.e./l.) induced an approximately fourfold increase in hydraulic conductivity, relative to the conductivity with distilled water. This enhanced conductivity did not change when the permeating solution was changed to sodium chloride solution (30 m.e./l.). But when distilled water was substituted for either the gypsum or sodium chloride solutions, the conductivity declined rapidly, but not to its pretreatment value. Possible mechanisms responsible for the conductivity changes are discussed.