The term “humus” dates back to the time of the Romans, when it was frequently used to designate the soil as a whole. It was later applied to the organic matter of soils and composts, or to different fractions of this organic matter; as well as, to complexes formed from a variety of natural organic substances.
Humus compounds are complex natural organic compounds that are formed in soils from plant residues, by a process of “humification”. Humus materials are complex aggregate of brown to dark colored amorphous substances, which have originated during the decomposition of plant and animal residues by microorganisms, under aerobic and anaerobic conditions, in soils, composts, peat bogs, and water basins. Chemically, humus consists of certain constituents of the original plant material resistant to further decomposition; of substances undergoing decomposition; of complexes resulting from decomposition, either by processes of hydrolysis or by oxidation and reduction; and of various compounds synthesized by microorganisms.
“Humic acid ” is the commercial term often used to refer to the combined humic and fulvic acid content found in these naturally occurring deposits. Humic acid is known to be among the most bio-chemically active materials found in soil.
Humic acid and related origin
Organic matter ,humic substance,humic acid ,humate and fulvic acid are closely related,all are come from the natural process of decaying plants and animals body.Organic matter is defined that all the organic substance in the soil with Hydrocarbonated base(containing hydrogen, carbon and oxygen).Humic substance is pure substance from process of humification with stronger Cation Exchange Capacity than clay.
Humic acids is the fraction of humic substance that is not soluble in acidic condition and soluble in higher PH solution with high molecular weight.Humate is humic acid salt is completely soluble in water extracted from humic acid after treating with high PH alkaline agentlike NAOH,KOH.Fulvic acid is defined as lower molecular weight soluble in both acidic and alkaline condition.
All of them are soil food and storage of mineral and water.For example,most dark color soil is much more fertile than light color soil,like most northeast part of China,they have a lot of dark color soil and most local peasant call it black soil.As black soil are from decaying plants mostly is humic substance has strong cation exchange capacity,easy to hold minerals and water.
Humic acid is made up of three different compounds, organic matter, humus, and humic substances. Organic matter is the plant and animal residue in the soil at various stages of decomposition. Humus is the end product of microbial degradation. Humic substances are naturally occurring organic materials with high molecular weights that are not easily degraded. The importance of humus, humic acids, and humates has long been recognized, but neither fully understood nor appreciated.