Abstract
Uncertainty involved in estimating water quality effects on soil permeability is an obstacle in appraising water quality for irrigation. This study examined salinity, sodicity and turbidity effects on hydraulic conductivity (HC) of three Torrifluvents ; Gila silt loam, Saneli clay loam and Glendale silty clay. HC was measured in laboratory columns containing initially dry aggregates (<2mm) at two bulk densities using ten saline solutions (electrical conductivity, EC of 0.4 to 4.8 dSm l, and sodium adsorption ratio, SAR of 0 to 20) with and without soil suspension. Hydraulic gradients, suspended solid concentrations of outflow, and aggregate size distributions were also measured. HC decreased at SAR less than 5 in all the tested soils, and the reduction followed an exponential form involving SAR/EC. Gila and Saneli soils developed surface seal, while Glendale silty clay that has shown swelling did not. The introduction of soil suspension into the saline solutions at a rate to form a depositional layer of less than 3 mm thick caused 4 to 7-fold reduction in HC of Gila and Saneli soils, but did not accentuate water quality effects on HC. The depositional layer did not reduce HC of Glendale soil. Increasing sodicity and/or reducing
salinity of saline solutions increased destruction of soil aggregates having a peak diameter of 0.18 mm, and HC was quantitatively related to the reduction in soil aggregates. Water intake into newly plowed and thoroughly disked soils may decrease at much lower SAR than commonly recognized, partly because of destruction of weak soil aggregates. The extent of reduction depends strongly on soil types. This results suggests that the soil permeabilty management requires the consideration of both soil properties and water quality.
