Veränderungen von Dreischicht-Tonmineralen durch natives K in holozänen Lößböden Mitteldeutschlands und Niederbayerns

Changes of three-layer clay minerals by native K in holocene loess derived soils of Central Germany and Lower Bavaria . Transformations of the clay minerals illite, vermiculite and smectite were determined in Central German (31 profiles) and Lower Bavarian loess districts (5 profiles) using 31–36 soil properties. To get significant differences between solum and sediment, the multivariate diskriminant analysis was applied. In the Central German loess district the following properties were crucial, to receive significant separation between solum-horizons and sediments: smectite content, several values of potassium fixation, interlattice potassium. Important were also some parameter of the K-Ca-exchange curve: Activity ratio documentclass{article}pagestyle{empty}begin{document}$ left({frac{{{rm aK}}}{{sqrt {{rm aCa}}}}} right) $end{document} of a soil solution in equilibrium with a soil (AR_o), buffering capacity of the soil for K at equilibrium (BCKE), labile K(K₁), exchange capacity of the exchange sites with a specific affinity for K minus labile K(EC_x—K₁). The differences of these values can be explained by assuming that (at pH 6–7) the beidellitic layers of smectites of the parent loess were transformed to illitic layers in the solum-horizons. In the Lower Bavarian loess landscape potassium fixation, total K in clay fraction (< 2 μm) and the parameters of the K-Ca-exchange curve indicate the same clay mineral transformation as in Central Germany. Smectite values were not introduced to the diskriminant function, because they were highly significantly correlated with potassium fixation. In this case potassium fixation has caused a better separation between the solum-horizons and the parent loess than X-ray data. From these results, from total -K of the fraction 2–20μm (solum-horizons smaller than sediments) and the vermiculite content fo the clay fraction, it can be concluded, that the rate of potassium release from micas and the rate of potassium fixation by beidellitic sheets during the Holocene period were nearly equal.