Effect of Low Electrolyte Concentration on Clay Dispersion and Hydraulic Conductivity of a Sodic Soil

Abstract

The changes in hydraulic conductivity and clay dispersivity of a Fallbrook soil (fine-loamy, mixed, thermic Typic Haploxeralfs) as a function of concentration (⩽ 3 meq/liter) and Na adsorption ratio (⩽ 30) of the percolating solutions were measured. Both phenomena were very sensitive to the level of exchangeable Na and to salt concentration of the soil solution. When the salt concentration is 3.0 meq/liter, the hydraulic conductivity and clay dispersion decrease if the exchangeable sodium percentage (ESP) values exceed 12. Conversely, in distilled water, clay dispersion and hydraulic conductivity decrease at ESP values as low as 1 to 2%. We hypothesize that mineral soils, which readily release salt during leaching with distilled water, will not be susceptible to exchangeable Na < 10%. Conversely, mineral soils with low rates of mineral dissolution, like the Fallbrook soil, should be susceptible even at lower ESP values. Also, surface soils, when leached with rainwater, will be especially susceptible at such low levels of exchangeable Na.