FIXATION AND RELEASE OF POTASSIUM IN RELATION TO THE MINERALOGY OF THE CLAY FRACTION OF SOME SELECTED SOIL HORIZON SAMPLES

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Abstract
Soil clays of 11 horizon samples of Canadian soils gave activity ratios (AReK) of 0.0003 to 0.0040, exchangeable K values of 0.18 to 1.74 meq/100 g, nonexchangeable K values of 1.54 to 6.65 meq/100 g upon leaching with 12 liters of 0.1 N BaCl2 and of 0.45 to 4.03 meq as measured by plant removal, and degrees of K-fixation of 29 to 100% of added K against extraction with 1 N NH4OAc. The amounts of exchangeable K were correlated with the activity ratios and with the amounts of non-exchangeable K removed by plants. Of the fixed K, 46 to 86% was recovered by leaching with the 0.1 N BaCl2 and 18 to 64% by cropping. Some of the clays gave a satisfactory relationship between their K behaviour and mineralogy. Two of them (Ae, Humo-Ferric Podzol), consisting of mixtures of vermiculite and montmorillonite, released native K slowly and had a high capacity to fix added K. Another corresponding sample, from the C horizon and consisting of well-ordered 2 M1 muscovite, also released native K slowly but gave the lowest degree of K-fixation. A predominantly montmorillonite clay with some mica layers (Gray Luvisol) gave a high release of native K and fixed an intermediate amount of added K. The K–mineralogy relationship in the remaining samples was less apparent, and varied with the complexity of interstratification.
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