CHARACTERIZATION OF THE ORGANIC MATTER ASSOCIATED WITH A SOIL CLAY

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Abstract
We characterized the organic matter associated with the fine clay fraction separated from the Ae horizon of a Typic Haplorthod, using chemical, infrared, carbon-13 nuclear magnetic resonance, and gas chromatographic-mass spectrometric methods. Infrared and 13C NMR spectra of the initial clay-organic complex showed the prominence of long-chain aliphatics. Extraction with 0.5 M NaOH removed substantial amounts of fulvic acid. n-Hexane and chloroform extracts contained n-alkanes, ranging from C16 to C35, long-chain alcohols, and more complex aliphatics. About half of the clay-associated organic matter consisted of humic materials; the other half was composed mainly of long-chain aliphatics. From the characteristics of the materials isolated and identified, it appears that the long-chain aliphatics have low mobilities in soils and that it is fulvic acid that is capable of penetrating clay interlayers. If aliphatics are present in clay interlayers, they have most likely been transported there by fulvic acid or other humic materials within which they are captured and that act as vehicles for the transport of hydrophobics within soil profiles.

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