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Chemical Nature of the Nitrogen in the Fulvic Fraction of Soil Organic Matter¹

ABSTRACT

A study of the forms of N in the fulvic fraction of soil organic matter showed that about one-half of the N occurred in compounds which deaminated readily by acid and base hydrolysis. About one-fourth of the N existed in amino acids; about one-tenth in amino sugars.

Through a modification of Forsyth's selective adsorption technique, the fulvic extract from a Brunizem soil was fractionated into several components, a number of which were pigmented. All of the components contained amino acids; several contained amino sugars. The N compounds which formed NH₃ by hydrolysis occurred primarily in association with pigments. A physicochemical study of the colloids of fulvic extracts showed that the colloids were heterogeneous with respect to both charge and particle size.

A consideration of possible mechanisms for the formation of fulvic pigments in soil prompted the author to postulate that the pigments originated through the condensation of carbonyl compounds with amino derivatives, by mechanisms similar to those proposed for browning processes in natural products.

Contribution from the Department of Agronomy, University of Illinois, Urbana. Published with the approval of the Director of the Illinois Agr. Exp. Sta. This investigation was supported in part by Consolidated Hatch Act Regional Research Funds. as a contributing project to Regional Project NC-17. Presented before Div. III, Soil Science Society of America, Cincinnati, Ohio, Nov. 16, 1959.

² Associate Professor in Soil Biology. Appreciation is expressed to Mr. Clyde Smith for performing many of the chemical determinations, and to Mr. Scott M. Savage and Miss Mary Louise McKenzie for making the electrophoresis and sedimentation measurements.

Received for publication March 8, 1960. Accepted for publication April 18, 1960.