Decreases in hydraulic conductivity with decreasing electrolyte concentration and increasing sodium adsorption ratio (SAR) of the percolating solution were assessed for seven soils of varying clay mineralogy. The decreases were particularly pronounced for soils high in 2:1 layer‐silicates, with the most labile hydraulic conductivities being exhibited by those soils containing the most montmorillonite. A soil containing considerable amorphous material was much more stable then the average, and a soil high in kaolinite and sesquioxides was virtually insensitive to variations in solution composition. No property of the solution alone was sufficient to characterize the response of the soils to a given solution, though expression of results in terms of the exchangeable sodium percentage (ESP) of the soil and the total salt concentration of the ambient solution produced more nearly similar curves for soils of similar clay mineralogy. The soils commonly demonstrated rather pronounced hydraulic conductivity decreases in the ESP range of 20 to 35 at salt concentrations of 3 to 50 meq/liter. The decreases were largely irreversible upon the reapplication of high salt or high Ca solutions to the soil, except for those soils containing greater than 10% montmorillonite on a whole‐soil basis.
Boron adsorption by Mexican and Hawaiian soils derived from volcanic ash deposits as influenced by solution phase concentration, reaction time, suspension pH, temperature, percent amorphous Al2O3 and SiO2, and free Fe2O3 content was studied. The adsorption was satisfactorily described by the Langmuir adsorption equation. Adsorption maxima were considerably greater than those observed for soils derived from other kinds of parent materials. In the range from 10 to 40C increases in temperature affected boron adsorption slightly. Maximum adsorption occurred between pH 8 and 9, suggesting that these soils have a greater affinity for B(OH)‐4‐B than for B(OH)3‐B. Boron adsorption by both the Mexican and Hawaiian soils was significantly correlated with amorphous SiO2 plus Al2O3 and amorphous Al2O3. However, higher correlation coefficients were obtained between boron adsorption and percent amorphous Al2O3. No significant correlations were found between boron adsorption and amorphous SiO2, and free F2O3 content.
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