IONIZATION OF CALCIUM FROM SOIL COLLOIDS AND ITS BEARING ON SOIL-PLANT RELATIONSHIPS

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Abstract
The following conclusions are drawn from an examination of the complete titration curves (including electrometric Na or Ca detns.) of Putnam clay (beidellite), Wyoming bentonite (montmorillonite), and kaolinite with NaOH and Ca(OH)2. In the montmorillonite and beidellite clays the fraction that is active varies abruptly for Na and for Ca at different stages of neutralization. Na shows a narrow zone and Ca a broad zone of very low activity. Kaolinite shows a fairly steady rise in fraction active for both cations as the amount of base is increased. These differences in active fraction reflect large differences in differential heat of adsorption of the cation in different regions of the titration curves. Exchange ions of a given kind are thus held with a wide range of bonding energies. Kaolinite shows great electrochemical differences from the montmorillonite clays. Ionization of all cations, but especially of Ca, is much greater for kaolinite than for the montmorillonite clays. The bearing of these results on the interpretation of practical field experience is discussed.

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