Humic Substances in soil organic matter
Soil Organic Matter is the organic matter from cadavers or living bodies' excreta in the soil. Soil Organic Matter is a kind of macromolecular substance with very complex structure. Under the coordination of microorganisms, there is another biochemical process in the soil, that is, the synthesis of some small molecule organic matter into a more complex macromolecular organic matter - humic substances. It's so-called humification process.
Humic substances is a kind of macromolecular organic polymer containing carbon, with very large molecular weight and complex structure. Humic substances is the organic matter which is beneficial to plant growth in soil. The scientists treated humus with sodium hydroxide and acid, and obtained some products with lower molecular weight: humic acid, fulvic acid and humin. Humic acid is the main component of humic substances. Fulvic acid was obtained by further acidification and decomposition of humic acid. Humic acids are widely exist in ocean, swamp, peat, soil and fresh water.
Leonardite is the most abundant resources with humic acid so far. It is the product of plant and animal residues after tens of millions of years of natural humification in the crust sedimentary layer. The fuel value of Leonardite is low, but it is an excellent humic acid resource. It has been calculated that the bioactivity of humic acid in some leonardite is 5 times higher than that of organic humic acid substances from other sources.