THE ISOLATION OF SOIL HUMIC AND FULVIC ACID COMPONENTS RICH IN "UNKNOWN NITROGEN"

Abstract

Close to 50% of the total N in soils has so far not been identified. Previous studies indicate that this "unknown" N might be bio-available and may participate in the soil N cycle. The objective of this investigation was to develop a procedure which would allow us to isolate from soils, fractions which were rich in unknown N but which would contain only small amounts of known N compounds. We felt that the availability of such fractions would permit us to learn more about the characteristics of the unknown N components without too much interference from the many known N-containing constituents. The isolation procedure involved (a) the extraction and separation of humic (HA) and fulvic acid (FA) fractions from soils; (b) hydrolysis of each fraction with hot 6 mol∙L −1 HCl; (c) separation of neutralized hydrolyzates on Sephadex G-25 gel; and (d) further separation of the highest molecular weight fractions of the neutralized hydrolyzates on G-50 gel, and of the second highest molecular weight fractions on G-15 gel. For soil samples taken from the Ah horizon of the Bainsville soil (a Humic Gleysol) and the Bh horizon of the Armadale (a Podzol), proportions of soil-N in HAs and FAs, and in fractions derived from them were, in HAs + FAs, 29.3 and 56.9%; in water-soluble, hydrolyzed HA- and FA- fractions, 12.0 and 19.7%; and in nonhydrolyzable and water-insoluble (at pH 7) fractions, 9.0 and 16.3%, respectively. Substantial portions of the soil N were left unextracted in the humins. Several fractions were isolated by the procedure described herein; in some close to 98% of the total N consisted of unknown N. Key words: Amino acid nitrogen, ammonia nitrogen, acid hydrolysis, gel filtration