Clay transformations following a leaching experiment on an acid brown soil

INRA, Cycles Biogeochimiques, Champenoux, France

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 period, the organic carbon content of the Al horizon had decreased by approximately 20% compared with the original horizon. In the leached Al horizon, the vermiculite layers of both the vermiculite and interstratified minerals were transformed into high-charge expanding layers, with the charge mainly located in the octahedral sheet. The inhibition of expansion 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 sesquioxide materials, especially in the interlayers of vermiculites. In both horizons, 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 NO (super -) ₃ leaching.

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