Humic substances, present in all soils and waters, come from decomposing plant elements. They can be fractionated by extraction into humin, humic acids, fulvic acids and ulmic acids. Its salts are called humates, fulvates and ulmates. Standing out as the main fraction, humic acids constitute the biological core of humus.

In fertile soil, the maximum concentration of humic acids reaches 3%, while peat has approximately 3% to 10%. In certain layers of soft lignite (Leonardite), which have not reached the lignite state, humic acids are found with concentrations of up to 85%. Leonardite is distinguished from lignite by a higher degree of oxidation and a higher content of humic acids, as noted above.

Since the discovery of this high concentration of humic acids in Leonardite, its commercial production for agriculture has experienced a notable increase.