Estimation of soil weathering stage and acid neutralizing capacity in a toposequence Luvisol-Cambisol on loess under deciduous forest in Belgium

Soils derived from loess are extensive in Europe and are well suited for fo restry. They are suspected to be poor acid buffers, however. We have estima ted the weathering stage and acid neutralizing capacity of acid soils under forest in a toposequence on loess in the Belgian silt belt. The soils vary distinctly in morphology and physico-chemical properties according to thei r topographic position. Dystric Cambisols have developed in colluvial depos its in the dry valley floors, whereas Dystric Luvisols have formed on the s lopes in a rejuvenated material. The Cambisols are more acid and less satur ated in bases than are Luvisols. They are strongly depleted of clay and con tain less weatherable minerals. Easily weatherable minerals are concentrate d mainly in the clay fraction of both soil types. Clay minerals of size < 2 mu m therefore act as major sinks for protons in these soils. A simplified expression taking into account the total reserve in bases, total aluminium and iron occluded in silicates is used to estimate acid neutralizing capac ity. Our estimates confirm that these acid loessic soils are indeed poor ac id buffers. They show that the Dystric Cambisols depleted of clay are sensi tive to potential acidification, whether natural or man-made.