Aluminium release in relation to the determination of cation exchange capacity of some podzolized New Zealand soils

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Abstract
SUMMARY: In upper mineral horizons, CEC by compulsive and isotopic exchange methods, using Ba2+ as the saturating cation, gave higher values than the effective CEC at natural soil pH, and much higher values than CEC determined with m NH4OAc at pH 7. Cumulative Al release during leaching was considerably higher using Mg2+ and Ba2+ chlorides than K+ and NH4+ chlorides, and gave a different shape extraction curve. Basal spacing of the dominant dioctahedral vermiculite in the soil clays contracted from 14.5Å to 10.0–10.9 Å when saturated with NH4+ and K+, restricting release of interlayer Al. Lower horizons, containing a large proportion of Al‐chlorite in the clay fraction, which did not contract with any of the cations, showed more normal exchange behaviour. On leaching, Al release was slightly greater with K+ and NH4+, than with Mg2+ and Ba2+, chlorides. The implication of the results for CEC measurements is discussed.