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Humic acid is a complex mixture of organic acids produced mostly by the decomposition of plant material, especially lignin. Humic acid is dark brown and is a major constituent of humus. It can also be found in peat, coal, and ocean water.
A substantial fraction of the mass of the humic acids is in carboxylic
acid functional groups, which endow these molecules with the ability to
chelate multivalent cations (Mg++, Ca++, Fe++,...). This chelation of ions
is probably the most important role of huic acids with respect to living
systems. By chelating the ions, they faciliate the uptake of these ions
by several mechanisms, one of which is preventing their precipitation,
another seems to be a direct and positive influence on their
bioavailability.
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