Abstract: The rates of K exchange of untreated and peroxide-treated micaceous clays from five Podzol soils of increasing degrees of weathering were determined using sodium tetraphenyl boron. In addition, the amounts of K fixed against NH4 were measured. The Ae horizon clays of these soils contained mainly interstratified mica-vermiculite-montmorillonite whereas the C horizon clays contained mica of a more discrete nature.
As was expected, there was an inverse relationship between rates of K exchange and degrees of weathering of the Ae horizon clays. However, in the samples from each of these soils except in those of the most weathered one, the K exchange rate of the interstratified mica from the Ae horizon was higher than that of the less weathered, more discrete mica from the corresponding C horizon. The abundance of hydrated edges and layers exposing K exchange sites in the Ae horizon micas probably contributed to their higher rates of K exchange. Amounts of K fixed in the Ae horizon clays were not related to degrees of weathering.
Removal of organic matter from the Ae horizon clays by peroxide considerably increased both the rates of K exchanged and the amounts of K fixed. These increases were attributed to the elimination of a blocking effect of adsorbed organic matter on K exchange and fixation.