Everyone who works in agriculture is aware of the basic lifecycle of crops: plants are seeded, they are nourished and they grow, they are harvested, and what is not consumed by (us) higher life forms is returned to the soil—where it is broken down through mineralization and by microorganisms so that it can be used to nourish the next cycle of crops. That relatively simple scenario is created by a wonderfully complex interchange of chemical, physical, and biological actions that scientists are still struggling to fully understand after 10,000 years of practical farming.
As with everything else on this planet, the story of humic substances begins and ends with carbon. All life on this planet is carbon-based: humans, animals, plants, insects, microorganisms . . . carbon is essential to building everything biological and keeping it powered and in working order. Plants pull carbon from the air (carbon dioxide) and through a series of reactions merge the carbon with energy from sunlight (photosynthesis) and hydrogen from water, eventually creating carbon-rich organic compounds required by plants throughout their metabolic pathways. A very important characteristic of carbon as an element is that it has a unique capacity to modify itself and, through functional group extensions, combine with many other elements to form shorter and longer carbon chains, rings, and complex organic compounds as required in the processes.