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THE INFLUENCE OF MAGNESIUM IN SALINE AND SODIC SOILS: A SPECIFIC EFFECT OR A PROBLEM OF CATION EXCHANGE?
Author(s) -
RAHMAN W. A.,
ROWELL D. L.
Publication year - 1979
Publication title -
journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 0022-4588
DOI - 10.1111/j.1365-2389.1979.tb01007.x
Subject(s) - vermiculite , illite , montmorillonite , electrolyte , chemistry , cation exchange capacity , ion exchange , magnesium , soil water , sodium , clay minerals , swelling , inorganic chemistry , dispersion (optics) , divalent , mineralogy , environmental chemistry , ion , soil science , geology , materials science , paleontology , physics , organic chemistry , electrode , optics , composite material
Summary Na‐Mg and Na‐Ca exchange isotherms were determined at electrolyte concentrations of 500, 50, 5 and 1 meq per litre for illite, vermiculite and montmorillonite and for three soils containing illite and montmorillonite. This enabled comparisons to be made of clay swelling, dispersion and soil hydraulic conductivity changes between the Na‐Mg and Na‐Ca systems at known SAR, ESP and electrolyte concentration. Na‐Mg montmoriUonite and a montmorillonitic soil behaved identically to the Na‐Ca systems at the same ESP and electrolyte concentration: there was no specific effect. At the same SAR, the higher ESP in the Na‐Mg system caused greater changes than in the Na‐Ca systems. The Na‐Mg vermiculite, illite, illitic soil and mixed illite‐montmorillonitic soil showed greater changes than the Na‐Ca systems at the same ESP, and there was a specific effect. At the same SAR, the higher ESP in all the Na‐Mg systems apart from vermiculite increased the differences, but for vermiculite with a lower ESP, the differences were reduced. The lack of a specific effect for montmorillonite is probably related to the demixing of cations with the divalent ions concentrated on the non‐swelling (internal) surfaces of the crystals.