Characterization of Humic Compounds

Abstract

The synthesis of humic substances has been the object of speculation for many years. Andreux (1994) distinguished lytic mechanisms (lysis of the cellular walls, proteolysis, ligninolysis, transformation of polyphenols and other organic components), the mechanisms of tanning and melanisation which include incorporation of nitrogen and oxygen (Maillard's reaction: condensation of carbohydrates in the presence of amino nitrogen, condensation of polyphenol and amino acids in oxidizing medium) and the incorporation of inherited compounds. Schnitzer (1978) reported the following four hypotheses about the formation of humic substances:-Deterioration of plant material. Certain fractions of plant tissues, particularly woody materials, are only superficially decomposed in the soil to form humic substances; the nature of this "inherited humus" is thus strongly influenced by the nature of the original plant material; the first stage of humification provides the heaviest humic substances which can then be broken down into lighter substances and ultimately into CO 2 and H 2 O.-Chemical polymerization. The plant materials break down into small molecules which are used as a source of energy and carbon by microorganisms ; these microorganisms then synthesize phenols and amino acids which are polymerized into humic substances; in this case the nature of original material has no effect on the type of substance formed.