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In general, fulvic acid has a higher amount of carboxylic groups and lower average molecular weight than does humic acid. Measured average molecular weights vary with source; however, molecular weight distributions of HA and FA overlap significantly. Age and origin of the source material determine the chemical structure of humic substances.
Due to their very complex molecular structure, humic substances, including humin, do not correspond to pure substances but consist of a mixture of many compounds that remain very difficult to characterize even using modern analytical techniques. [2]
Heat is used to increase the solubility of humic acids and hence more potassium humate can be extracted. The resulting liquid is dried to produce the amorphous crystalline like product which can then be added as a granule to fertilizer. The potassium humate granules by way of chemical extraction lose their hydrophobic properties and are now ...
However, some authors [16] suggest that complex soil organic molecules may be much less stable than previously thought: "the available evidence does not support the formation of large-molecular-size and persistent 'humic substances' in soils. Instead, soil organic matter is a continuum of progressively decomposing organic compounds.″
Fulvic acid is the genus that contains the matter that has the lowest molecular weight, is soluble in acids and alkalis, and is susceptible to microbial action. Humic acid is the genus that contains the intermediate matter that has medial molecular weight, is soluble in alkalis and insoluble in acids, and has some resistance to microbial action.
The carbon increases the organic matter in the soil while the biological control microbes provide an alternative to chemical pesticides. [35] Leonardite is a soil conditioner rich in humic acids that is formed by natural oxidation when lignite comes in contact with air. [36] The process can be replicated artificially on a large scale. [37]
Apparently "humic substance" is a relatively rarely used term and concept, which refers to compounds present in untreated humus; whereas "humic acid", "fulvic acid" and "humin" are not "humic substances", but compounds derived from humus by chemical treatment. While "humic acid" and "fulvic acid" have indefinite chemical composition, they are ...
Humic acids and fulvic acids, which begin as raw organic matter, are important constituents of humus. After the death of plants, animals, and microbes, microbes begin to feed on the residues through their production of extra-cellular soil enzymes, resulting finally in the formation of humus. [ 162 ]