Incipient podzolization and weathering caused by complexation in a forest Cambisol on loess as revealed by a soil solution study

Surface podzolization has so far been diagnosed from morphological observat ions, selective extraction and mineralogical investigations. We studied thi s process in two Cambisol profiles developed in loess, one with a fibrimor humus and the other with a dysmoder humus, by characterizing the chemical c omposition and the complexing properties of the soil solution. The solution s were sampled bimonthly for 3 years at four depths (4, 8, 13, 25 cm) using both zero-tension and low-tension capillary-wick lysimeters. The leachates from the Ah horizon of the soil with fibrimor contained less nitrate, sulp hate and calcium than those from the one with a dysmoder because there was less bioturbation and mineralization in it. Both the complexation capacity and the density of ligand binding sites were larger in the soil solutions o f the Ah (4 cm) and AB (8 cm) horizons of the soil with the fibrimor. In th is soil, the complexing properties of the liquid phase induced a depletion of inorganic monomeric aluminium. In this environment, the hydroxy interlay ered 2:1 clay minerals lose their Al-interlayers and transform into vermicu lite and smectite, which in turn weather, producing large amounts of magnes ium in the soil solution. This was found to be a major characteristic of we athering by complexation and incipient podzolization in the Cambisol with t he fibrimor. In this process, nitric acid probably contributes to mineral d issolution.