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Macroscopic Swelling and Hydraulic Conductivity Properties of Four Vermiculitic Soils¹

ABSTRACT

The extent to which mixed Na, Ca electrolyte solutions affected the hydraulic conductivity and macroscopic swelling properties of four vermiculitic soils was determined. Macroscopic swelling did not occur in the < 5µ fraction of the soils until exchangeable-sodium-percentage (ESP) values in excess of 30 to 60 and electrolyte concentrations of less than 20 meq/liter were established. Decreases in hydraulic conductivities (HC) of soils devoid of montmorillonite did not occur at ESP values of less than 50 in the absence of mechanical and chemical disaggregation. After disaggregation, decreases in HC occurred in the ESP range of 10–40 at electrolyte concentrations of 5–10 meq/liter. The concept of "inactive exchangeable Na" residing in nonclay-sized vermiculite particles is introduced.

¹ Contribution from US Salinity Laboratory, Soil & Water Conservation Research Division, ARS, USDA, Riverside, Calif., in cooperation with the 17 Western States and Hawaii.

² Research Soil Chemist and Chemist, respectively, US Salinity Laboratory, Riverside, Calif.

Received for publication September 17, 1968. Accepted for publication January 13, 1969.