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The Effect of Interactions of Salts and Clays on Unsaturated Water Flow¹

ABSTRACT

Artificial soils containing 17.6% dickite or montmorillonite clay minerals were treated to give exchangeable sodium percentages (ESP) of 5.0 and 20.3, and 5.5 and 13.6, respectively. Calcium chloride solutions of 0 or 0.015 meq/ml were applied to horizontal columns of the soils at 2 millibars tension. Deviation of the least squares line fit to data of quantity of water entry or distance of water movement vs. time from 0 at time = 0 was taken as an indication of swelling. By this criteria, swelling was not a factor in water movement in dickite soil regardless of treatment but was a factor in water movement in montmorillonite soil. Use of 0.015NCaCl₂ solution eliminated swelling in the 5.5 ESP montmorillonite soil but only reduced swelling in the 13.6 ESP soil.

Water diffusivities were calculated from water content vs. distance curves. Use of 0.015N CaCl₂ increased water diffusivity by a factor of at least 1.8 in all soils except montmorillonite ESP 13.6. This is probably associated with a reduced influence of the double layer on water movement as well as a change in pore geometry. By the method of calculations, use of 0.015N CaCl₂ did not increase the diffusivity of montmorillonite ESP 13.6 over that of distilled water in spite of reduced swelling.

Both water treatments resulted in some Na displacement from the first few centimeters of the columns and movement with the wetted front, but the quantity of Na movement was much greater with the CaCl₂ solution.

¹ Part of a thesis submitted by the senior author in partial fulfillment of requirements of the M.S. degree. Approved as Montana Agr. Exp. Sta. Research Paper no. 731. Financial assistance from the Bureau of Reclamation is gratefully acknowledged.

² Formerly Graduate Assistant, now Instructor, Michigan State University, East Lansing, and Professor of Soils, respectively.

Received for publication February 7, 1966. Accepted for publication June 7, 1966.