CLAY MINERAL TRANSFORMATIONS IN SOILS AS INFLUENCED BY POTASSIUM RELEASE FROM BIOTITE

Abstract

In a closed system column experiment, 0.005 M CaCl2 solutions were percolated through 2 different soils, with a thin layer of freshly ground biotite on top of the column. The K release from the biotite was influenced by the clay mineralogy of the soils. For a loess soil containing interstratified illite-smectite, typical for loess deposits in southern Germany, the rate of K release was significantly higher than that for a clay soil derived from Amaltheen claystone with illite and some vermiculite in its clay fraction. For both soils, K buffering capacity, as well as K fixing capacity, decreased during the contact with biotite, this tendency being more pronounced in the loess soil. Equilibrium K-Ca-activity ratios increased with time, but were permanently higher in the clay soil than in the loess soil. In the loess soil, lithogenic smectite was transformed into illite in all clay subfractions. Vermiculite into illite transformation is important only in the coarse clay. The illites formed by these reactions have lower K contents than detrital illites.