Prediction of unsaturated hydraulic conductivity changes of a loamy soil in different salt solutions by using the equivalent salt solutions concept

Jayawardane, N.S.

Australian Journal of Soil Research 30(5): 565-571

1992


Accession: 002191527

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Abstract
Equivalent salt solutions series have been previously defined as solutions with combinations of sodium absorption ratio (SAR) and electrolyte concentration (E-c) producing the same extent of clay swelling in a given soil. These equivalent salt solutions series values have yielded satisfactory predictions of changes in saturated hydrauli conductivity, with changes in salt solution composition and concentrations. In the present study, previously published data on changes in saturated and unsaturated hydraulic conductivites of Gilat soil in salt solutions of cationic ratio 0-50 (mmol dm-3) 1/2 and electrolyte concentration 2-50 (m.e. dm-3) were used to compare the equivalent salt solution series values for hydraulic conductivities at different water contents. The equivalent salt solution series causing a given change in saturated hydraulic conductivity of a loamy Gilat soil were derived. These equivalent salt solution values were used to predict the unsaturated hydraulic conductivities of this soil at low water contents. Predictions of unsaturated conductivity at relative water contents THETA ranging from 0.80 to 0.20 agreed closely with the measured values. Coefficients log alpha-1 and b-1 for Gilat soil, in the equation log E-c = log alpha-1+b-1 log SAR, relating the E-c and SAR values of each equivalent salt solutions series were determined at THETA values between 1.00 and 0.20. The relationship between log alpha-1 and b-1 was similar at all water contents, in agreement with the equivalent salt solutions concept. Therefore, equivalent salt solution parameters derived from saturated hydraulic conductivity measurements could be used to predict changes in unsaturated conductivities and hence flow rates of saline water under specified boundary conditions.