CHANGES OF MINERALOGICAL AND SURFACE PROPERT IES OF WATER D ISPERSIBLE CLAY AFTER ACID TREATMENT OF SOILS

A B S TRACT: Mineralogical and water adsorption properties of water dispersible clays extracted from five soils of different ypology after treatment with acid to different pH levels, were studied. The mineral composition, total and divalent iron content, surface areas and average adsorption energies of water dispersible clays were complicated functions of pH, reflecting the simultaneous effects of mineral destruction and aggregate disruption processes under influence of protons on soils. The magnetic susceptibilities of water dispersible clays were the lowest at pH 2 and roughly constant at higher pH values indicating the dissolution of crystalline forms of Fe below pH 3. The broadening of the peaks of adsorption energy distribution functions with decrease in pH is related to increasing formation of amorphous material from mineral phases. Since the mid 1980s, soil acidification has been a subject of intensive research in many countries (Dechnik et al., 1990; Ulrich et al., 1980). One of the most important results of acidification processes is the intensive destruction of clay minerals and other silicates and accumulation of poorly crystal-lized and amorphous material (Verhoff & Brummer, 1991, 1993). This is connected with the trend of structural deterioration of soils as the degree of leaching intensifies (Dilkova & Kerchev, 1990). Since water dispersible clay (WDC) is a valuable indicator of soil aggregation status reflecting soil erodibil ity, crusting, water infi ltration, etc. (Walczak, 1984; Brubaker et al., 1992) model experiments of soil acidification were undertaken focusing on the qualitative and quantitative changes of the WDC due to acid treatment of soils. MATERIALS AND METHODS Samples were taken from humus horizons of the following five soils from the eastern part of th