Nature of soil carbohydrate and its association with soil humic substances |
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| Authors: | M V CHESHIRE J D RUSSELL A R FRASER J M BRACEWELL G W ROBERTSONS‡ L M BENZING-PURDIE C I RATCLIFFE† J A RIPMEESTER† B A GOODMAN‡ |
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| Institution: | Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen AB9 2QJ, UK;Probities and Strategies Directorate, Research Branch, Agriculture Canada, Ottawa K1A 0C5, Canada;Division of Chemistry, National Research Council, Ottawa KA1 0R6, Canada;Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, UK |
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| Abstract: | The fulvic acid and alkali-soluble polysaccharide fractions of a sandy loam arable soil of the Countesswells series have been subjected to acid hydrolysis or methylation and the products examined by infra-red and NMR spectroscopy, pyrolysis mass spectrometry and chemical analysis. Infra-red and NMR spectroscopy of the polysaccharide fraction indicated that the substance was predominantly carbohydrate, although sugars accounted for less than one-third of the weight by chemical analysis. Pyrolysis mass spectrometry con-firmed the presence of sugars by sugar anhydride formation, but also showed the presence of ‘secondary’ or ‘pseudo’ polysaccharide. The fulvic acid contained only 2–3% sugars by chemical analysis, whereas a much larger carbohydrate component was suggested by physicochemical analyses. Infra-red and pyrolysis mass spectrometry difference spectra for the residues after acid hydrolysis indicated the release of material with some of the characteristics of glycoprotein. Most of the carbohydrate present in the fulvic acid was of the secondary or pseudo polysaccharide type. The hypothesis that the secondary polysaccharide could be a degraded polysaccharide structure in which some sugar residues have been partly transformed to melanoidins by Maillard reaction is explored. |
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