Humic Acids

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Humic Acids


dark-colored amorphous organic substances of high molecular weight, the structure of which has not been conclusively established.

Humic acids are present in peats (about 50 percent) and sooty lignites (about 60 percent); they are less abundant in compact and transitional coals, and they vary from 0 to 100 percent of the organic matter (depending on the degree of weathering) in weathered brown and pit coal. In soils the humic acid content is highest in chernozem (to 10 percent). Humic acids are produced by the bacterial decomposition of dead plant residues and by the prolonged action of atmospheric oxygen or stratal water on organic matter.

The structure of humic acids is determined by the presence of weakly condensed and substituted aromatic nuclei interlinked by parts of a nonaromatic nature. The molecules consist of carboxyl and carbonyl groups, alcoholic and phenolic hydroxyls, and (sometimes) methoxyl groups. Dark solutions are formed when an alkali acts on humic acids. The acids are precipitated in the form of swollen gels from these solutions after exposure to acids and salt solutions of higher-valence metals. Humic acids have the capacity for ion-exchange reactions forming soluble and insoluble humates. Humic acids are powerful geochemical agents that help to break down rocks and minerals; they help to concentrate, scatter, and redeposit elements in the earth’s crust. They are the main constituent of the organic matter in soil (humus), which is responsible for soil fertility.

Humic acids are used in the production of lead accumulators and in stabilizing slurries when drilling wells. They are also plant growth stimulants and components of organic mineral (humic) fertilizers.


Stadnikov, G. L. Proiskhozhdenie uglei i nefti, 3rd ed. Moscow-Leningrad, 1937.
Kukharenko, T. A. “Sovremennoe sostoianie nashikh znanii o strukture i svoistvakhguminovykh kislot iskopaemykh ugley.” Tr. in-ta goriuchikh iskopaemykh, 1955, issue 5.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Conversely, what management activities increase humic acid and organic matter in our soils?
Humic acid was added in the form of a humic acid salt (potassium humate, PH, NUTRICO, Johannesburg, South Africa).
Due to the quadratic behavior of these variables, it was possible to verify that doses of humic acids lower than 200 mg C [L.sub.-1] (Table 3) would provide greater SD (131.15 mg C [L.sup.-1]), H (161.9 mg C [L.sup.-1]), NL (148.69 mg C [L.sup.-1]) e LA (148.52 mg C [L.sup.-1]).
Phosphorus (P) extracted with Mehlich-1 of Caption: Latosol incubated with doses of peat (A) and leonardite (B) humic acids and doses of P, without (pH 4.5) and with (pH 7.0) acidity correction
The treatments consisted of two K fertilisers, regular KCl and KCl coated with humic acid, applied in single dose or split, broadcast on the soil surface.
In the T1, T2, T3, T4, and T5 substrates the molecular absorption spectroscopic techniques in the ultraviolet-visible region, with bands at 270 and 390 nm (aromatic), of the humic acids showed humification.
Richard, "Hydrophobicity of electrophoretic fractions of different soil humic acids," Journal of Soils and Sediments, vol.
FIGURE 2: Organic Carbon content on fractions of the humic substances (SH): fulvic acids (AF), humic acids (AH), humin (HUM), and non-humic substances (SNH) on Humic Cambisol from areas under native grassland (CN), five-year old Pinus (P05), sixteen-year old Pinus (P16), and twenty-one-year old Pinus (P21) (Graph A) and proportion of these chemical fractions related to total organic carbon (TOC) (Graph B).
Interactions between humic acids and metal ions have a complex nature given by their heterogeneous, polyelectrolyte, and polydispersive character.