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Calcium-magnesium exchange equilibria were studied in several New Zealand topsoils. All soils showed a preference for calcium which increased with increasing proportion of magnesium in the equilibrium solution (XMg) Soils containing allophane had greater (P <0.05) selectivity preference for calcium than the 'non-allophanic' soils and had significantly (P <0.05) higher contents of organic carbon and Tamm's aluminium.
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DC Edmeades (1980) studied this question.
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