Humic Acids

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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.


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Kukharenko, T. A. “Sovremennoe sostoianie nashikh znanii o strukture i svoistvakhguminovykh kislot iskopaemykh ugley.” Tr. in-ta goriuchikh iskopaemykh, 1955, issue 5.
References in periodicals archive ?
TABLE 1: Organic carbon (C) content on 0-40 cm soil layer in the fulvic acids (AF), humic acids (AH) and humin (HUM) of humic substances and sum of these three fractions (SOMA) on four situations of soil use in a Humic Dystrupept in southern Brazilian highlands.
Humic acids buffer the effects of urea on soil ammonia oxidizers and potential nitrification.
2007) in long-term fertilizer experiment noted that the contents of humin, humic acid and fulvic acid in the soil were significantly increased with the application of fertilizer and FYM which could be due to the improved soil organic matter and conducive environment for the formation of humic acid in Typic Haplusteps.
The Experiment was conducted to investigate the response of banana plants to microelements (ME), humic acid (H.
Klumpp, The Role of Reactive Surface Sites and Complexation by Humic Acids in the Interaction of Clay Mineral and Iron Oxide Particles, Org.
Separating fulvic and humic acids could be done through centrifugation at 6,000 rpm for 15 minutes, and then sifted using Watman 42 paper.