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Analytical Properties of the Soluble, Metal-complexing Fractions in Sludge-Soil Mixtures: V. Amino Acids, Hexosamines, and Other Carbohydrates in Fulvic Acid¹

ABSTRACT

The quantitative distribution of amino acids, hexosamines, and other carbohydrates was determined for three representative, purified fulvic acids extracted from anaerobically-digested sewage sludges. The amino acid content ranged from 5 to 9 wt % in the three fulvic acids and the distribution of acidic, neutral, and basic amino acids generally was similar to that in soil-derived fulvic acids. The principal difference between the two types of fulvic acid was with the S-containing amino acids, which were more abundant in the sludge-derived fulvic acids. The content of galactosamine was very high in the three fulvic acids studied, with the result that the glucosamine/galactosamine ratio was about an order of magnitude lower in these fulvic acids than what is typical for soil-derived fulvic acids. The content of neutral and acidic sugars ranged from 12 to 25 wt % in the fulvic acids, with a distribution of neutral sugars that was similar to what is found typically in natural soil organic matter. Thus the amino acid, hexosamine, and carbohydrate components of sludge-derived fulvic acid may account for up to 50 wt % of this material. The major differences among these components between sludge-derived and soil-derived fulvic acids appear to be related to the high sulfur content of the sludge-derived fulvic acids and their expected high content of anaerobic bacterial residues.

¹ Contribution from the Dep. of Soil and Environmental Sciences, University of California, Riverside, CA 92521.

² Research Associate IV, Visiting Professor, Research Associate II, Professor of Soil Science, Research Associate III, and Graduate Research Assistant, respectively. Present address of Dr. Schaumberg is Dep. of Chemistry, Sonoma State Univ., Rohnert Park, CA 94928. Permanent address of Mr. Heick is Dep. of Plant Pathology, Univ. of California, Riverside.

Received for publication November 15, 1979. Accepted for publication March 4, 1980.