IMOGOLITE AND PROTO-IMOGOLITE ALLOPHANE IN SPODIC HORIZONS: EVIDENCE FOR A MOBILE ALUMINIUM SILICATE COMPLEX IN PODZOL FORMATION |
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| Authors: | V C FARMER J D RUSSELL M L BERROW |
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| Institution: | Department of Spectrochemistry, The Macaulay Institute far Soil Research, Craigiebuckler, Aberdeen |
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| Abstract: | Examination by infrared spectroscopy and electron microscopy of the fine clays (<0.5 μm) dispersed at pH 3.5 from H2O2-treated soil indicates that imogolite and proto-imogolite allophanes are concentrated in podzolic B2 and B3 horizons, and make up at least 6 percent of one B2 horizon soil, which contains virtually no layer silicate clays. It is argued here that imogolite-type components are the principal source of extractable aluminium and silicon in such horizons, that they may act as cementing agents in indurated horizons, and that proto-imogolite, a soluble aluminium-silicate complex, is the predominant mobile form in which aluminium is transported to B2 and lower horizons of podzols. Comparison of the amounts of aluminium extracted by acetic acid with those extracted by EDTA indicates that extractable aluminium in Bhg, Bh, and organic-rich A2 horizons is present principally in organic complexes. It is proposed that the aluminium fulvates concentrated in these horizons are formed in situ. |
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