EFFECT OF MIXED NA/CA SOLUTIONS ON SWELLING, DISPERSION AND TRANSIENT WATER-FLOW IN UNSATURATED MONTMORILLONITIC SOILS

The effects of Na/Ca solutions of differing sodium adsorption ratio (SAR) and electrolyte concentration (C) on swelling, dispersion, soil water penetrability (lambda), diffusivity D(theta), water retention curve (WRC) and unsaturated hydraulic conductivity K(theta) at four montmorillonitic soil samples were investigated. Swelling and dispersion increased when SAR increased and/or C decreased. Penetrability and K(theta) decreased with increase in SAR and/or decrease in C.D(theta) increased with increase in water content, decrease in clay content and/or increase in C. At high water content, clay content and C there was an increase in D(theta) associated with increase in SAR. The water retention in the four samples increased when SAR increased and/or C decreased. The slopes of WRC which represent soil water capacity C(theta) had higher values when SAR decreased and/or C increased. The reduction in unsaturated water flow at high SAR and/or low C was attributed to changes in microstructure. The relationships between any given soil physical conditions and SAR and/or C were generally continuous functions. Hydraulic properties of montmorillonitic soils cannot be specified independently of water quality.