Soil development of three Chernozem-like profiles from North Bulgaria revealed by magnetic studies

A detailed magnetic study of three soil profiles of Calcic Chernozem, Luvic Phaeozem and Orthic Luvisol, described in the Soil Atlas of Bulgaria, was carried out in order to reveal the potential of magnetic methods for characterization of soil forming processes and properties of pedogenic iron oxides. Thermomagnetic analysis of susceptibility and SEM/EDX observations revealed that the main pedogenic mineral in all three soils is fine grained superparamagnetic to single domain maghemite. Thermal stability of this pedogenic phase up to temperatures of 500 °C is revealed by the partial thermomagnetic analyses of susceptibility. Depth variations of magnetic parameters and ratios point to the presence of stable single-domain to pseudo-single domain grains in humic horizons, the quantity of which decreases sharply towards lower soil horizons. These magnetic grain size changes are best expressed in Orthic Luvisol and reflect intensified processes of translocation of substances downward.