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.
Seen as different, soil clays become more important to soils and also beyond soils
