Humic substances are organic compounds that are important components of humus, the major organic fraction of soil, peat, and coal (and also a constituent of many upland streams, dystrophic lakes, and ocean water). For a long era in the 19th and 20th centuries, humic substances were often viewed through a lens of acid-base theory that described humic acids, like organic acids, and their conjugate bases, humates, as important components of organic matter. Trial Reports. Through this viewpoint, humic acids were defined as organic substances extracted from soil that coagulate (form small solid pieces) when a strong-base extract is acidified, whereas fulvic acids are organic acids that remain soluble (stay dissolved) when a strong-base extract is acidified. Humic matter in isolation is the result of chemical extraction from the soil organic matter or the dissolved organic matter and represents the humic molecules distributed in the soil or water. A new understanding views humic substances not as high-molecular-weight macropolymers but as heterogeneous and relatively small molecular components of the soil organic matter auto-assembled in supramolecular associations and composed of a variety of compounds of biological origin and synthesized by abiotic and biotic reactions in the soil. It is the large molecular complexity of the soil humeome that confers to humic matter its bioactivity in soil and its role as a plant growth promoter.