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Reduced Sodium Exchange Capacity in Unsaturated Flow¹

ABSTRACT

Flowing water with a reduced degree of saturation seems to reduce the apparent or effective cation-exchange capacity. The experiment was performed by running water through a layered soil, thus obtaining unsaturated flow conditions. It is suggested that the flow direction induces anisotropy with respect to molecular diffusion. The hydrodynamic dispersion in the flow direction is almost unaffected. At the same time there must be some locations off the main water stream with which there is negligible mixing or molecular exchange by diffusion. One may associate to these isolated locations a prevailing direction normal to the mainstream. In this case, it can be said that the unsaturated flow induces anisotropy on ion transfer by mixing or molecular diffusion.

¹ The experimental work was supported by the Israel Atomic Energy Commission and carried out at the National and University Institute of Agriculture, Rehovoth, Israel. The senior author while in the Technion, Israel Institute of Technology, Haifa, revised some of the experimental results in view of the new concept of an induced anisotropy. The draft of this article was prepared before June 1967. It was revised after Dr. Mokady was killed in the war. Dan Zaslavsky, a colleague of the senior author, has given material assistance in revising the manuscript, and in attempting to ensure that Dr. Mokady's ideas and concepts have been correctly set forth.

² Senior Lecturer, Technion, Haifa, Israel, and Soil Scientist, Ministry of Agriculture, Tel Aviv, Israel, respectively.

Received for publication December 14, 1967. Accepted for publication April 17, 1968.