Characteristics and Uses

Characteristics

Humic substances are divided into three crude fractions based on their solubilities in aqueous bases and acids:

• Humic acids consist of dark brown to black humic substances that are soluble in dilute alkali solutions but are precipitated under acidification (pH<2) of the alkaline extract.

• Fulvic acids consist of light yellow to yellow-brown humic substances that are soluble in both dilute alkali and dilute acid solutions.

• Humin consists of black-colored humic substances that cannot be extracted from soil by dilute base or acid.

Differences among fulvic and humic acids and humin occur because of variations in the degree of polymerization, molecular weight, and number of functional groups as depicted in the following illustration (adapted from Stevenson, 1982):

Uses

A variety of uses have been developed for humic acids due to their coloration, swelling potential when wetted, ability to chelate with metals, and ability to form complex water- soluble and -insoluble compounds. Typical uses include soil conditioner/stabilizer, drilling mud additive, deodorizer/air freshener, mud bath additive, pigments for printing inks, fertilizers, growth hormones for plants, flotation reagent, chelation/metal ion adsorption, ion exchange resin, mortar/cement additive, and cattle feed supplement.

Fulvic acids are typically used as dietary supplements and soil conditioners.

References

Schnitzer, M. 1978. Humic Substances: Chemistry and Reactions. p. 1-64. In M. Schnitzer and S. U. Khan (ed.) Soil Organic Matter. Elsevier North-Holland, Inc. New York.

Stevenson, F. J. 1982. Humus Chemistry - Genesis, Composition, Reactions. John Wiley and Sons. New York.