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Properties and Decomposition and Binding Action in Soil of "Humic Acid" Synthesized by Epicoccum nigrum¹

ABSTRACT

Epicoccum nigrum cultured in a glucose-asparagine or glucose peptone medium synthesized a "humic acid" in yields of 2 to 6g from 15 l of medium. The fugnus "humic acid" and the humic acid fraction from leonardite used for comparison were both highly resistant to decomposition in soil and significantly improved soil aggregation and hydraulic conductivity at 0.1 to 0.5% concentrations. The carbon content ranged from 53 to 59% and the Nitrogen of most samples from 6 to 8.5. As the pH of the nutrient medium at termination of incubation increased, the nitrogen content of the humic acid fraction increased. Total acidity, COOH groups, phenolic OH groups, exchange capacity at different pH values, and molecular weights were all within the ranges reported for humic acids of soils and peats. Following reductive degradation with sodium amalgam and acidification to pH 1.0, ether extractable substances equivalent to 15 to 20% of the acid hydrolyzed humic acid were recovered. Chromatographic analysis of the ether extract separated 14 phenols including orcinol, orsellinic acid, 2, 4-dihydroxy toluene, 2, 4-dihydroxy-benzoic acid, 3, 5-dihydroxybenzoic acid, 2, 4, 5-trihydroxy toluene, and 2, 3, 5-trihydroxy toluene. From 30 to 48% of the nitrogen in the humic acid was released by proteases or hydrolysis with HCl.

Key Words: aggregation, soil • phenols • molecular weight

¹ Joint contribution University of California Citrus Research Center and Agricultural Experiment Station, Riverside, California and Institut für Biochemie des Bodens, Forschungsanstalt für Landwirtschaft, Braunschweig, Germany.

² Professor of Soil Science and Professor of Soil Physics, respectively, University of California, Riverside, and Biochemist, Institut für Biochemie des Bodens, Braunschweig, Germany. The authors give thanks to J. O. Ervin, J. Warneke, R. Shepherd, Miss Ellen Pleiss and E. Baume for laboratory assistance; Dr. J. C. Salfeld for furnishing equipment for thin-layer chromatography and sodium amalgum reduction of humic acid; to Dr. H. Söchtig for making some of the sephadex gel measurements; and Dr. W. Flaig for helpful suggestions

Received for publication January 11, 1967. Accepted for publication March 17, 1967.