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The Value of Humic Substances in the Carbon Lifecycle of Crops

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1 © 2017, Bio Huma Netics Inc. The Value of Humic Substances Publication No. HG-170215-01 The Value of Humic Substances in the Carbon Lifecycle of Crops: Humic Acids, Fulvic Acids, and Beyond. By Larry Cooper, with Rita Abi-Ghanem, PhD E veryone 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. 1 What Are Humic Substances? When plants end their life cycle, their components are decomposed through the aid of mineralization and microorganisms and returned to the soil as organic matter. About 70% of soil organic matter is humus, a brown to black complex variable of carbon-containing compounds that is slow to decompose under natural conditions and can persist in the soil for several hundred years. The humic substances that, in turn, make up humus are relatively large organic carbon-chain complexes that are composed of carbon, oxygen, hydrogen, nitrogen, and sulfur. These humic substances, which contribute to the brown or black color of surface soils, can be divided into three major categories: humin, humic acids (HAs), and fulvic acids (FAs). 2 (See Fig. 1.) These are functional categories based largely on molecular size and their solubility in water adjusted to different pH conditions. 3 Humins are very large molecules (molecular weight of 100,000 to 10,000,000 Da) that are not soluble in water at any pH level and are, consequently, very slow to break down. Within soil, humin improves structure, water- holding capacity, and stability. Humin also functions as a cation exchange system that aids the soil's ability to storehouse plant nutrients. Humic acids have a smaller molecular size than humins (molecular weight of 50,000 to 100,000 Da, with 1,000s of carbon rings) and are soluble in water under alkaline conditions. Because other elements readily bind to humic acid molecules in a form that can be easily absorbed by The following article was originally published in the January 2017 issue of AgroPages Magazine. Humic substances play an important role in soil fertility and crop yield. This article provides a basic overview of what humic substances are, how they are created, and how they work. Discussion is provided on how to add humic content to crop soil, including the use of commercial products such as the Huma Gro ® line of carbon-rich organic acids. Figure 1. Chemical Properties of Humic Substances 4

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