Cation exchange resin and test vermiculite to study soil processes in situ in a toposequence of Luvisol and Cambisol on loess

Both the ion accumulation on cation exchange resin and the transformation of test vermiculite in situ have been used to identify current processes in acid forest soils. We used such test materials to study weathering in a toposequence Dystric Luvisol–Spodo‐Dystric Cambisol on loess under deciduous forest in Belgium. The resin and a trioctahedral vermiculite were inserted for 2 years in the major horizons, down to a depth of 60 cm. The cation accumulation on the resin revealed that four main acid‐consuming systems are currently active in the toposequence. With decreasing acid neutralizing capacity, these systems are in the Luvisols: (i) the pool of exchangeable bases, (ii) the Al‐bearing minerals controlling the Al concentration in the liquid phase; and in the podzolized Cambisols: (iii) the less weatherable K‐bearing minerals, (iv) the Mg‐bearing phyllosilicates made free of Al interlayers in complexing conditions. The loss of cation exchange capacity in the test vermiculite is related to Al interlayering. However, this process masks a significant interlayer accumulation of magnesium, which is generated by the weathering of the test mineral itself. The largest interlayer accumulation of Mg occurs in the podzolized Cambisol, suggesting more intense weathering of the test vermiculite in this soil.