CLAY TRANSFORMATIONS FOLLOWING A LEACHING EXPERIMENT ON AN ACID BROWNSOIL

The chemical and mineralogical properties of the Al and B horizons of an acid brown soil (typic Dystrochrept) were compared before and after a 20 month column leaching experiment. At the end of the leaching per iod, the organic carbon content of the Al horizon had decreased by sim ilar to 20% compared with the original horizon. In the leached Al hori zon, the vermiculite layers of both the vermiculite and interstratifie d minerals were transformed into high-charge expanding layers, with th e charge mainly located in the octahedral sheet. The inhibition of exp ansion properties by pretreatment with dithionite-citrate-bicarbonate (DCB) was explained by an increase in total layer charge induced by Fe reduction. In the B horizon, leaching resulted in a loss of sesquioxi de materials, especially in the interlayers of vermiculites. In both h orizons, the amounts of Al extracted by Na citrate and the amounts of Fe extracted by DCB decreased. Analysis of solution composition showed that Al mobilization was closely associated with NO3- leaching.