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The Value of Humic Substances in the Carbon Lifecycle of Crops

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2 The Value of Humic Substances HumaGro.com 800.961.1220 plants and microorganisms, humic acids function as important ion exchange and chelating systems. Fulvic acids have molecules that are smaller than humic acids (molecular weight of 5,000 to 10,000 Da, with 100s of carbon rings), are water soluble at all pH levels, and have a higher oxygen content than humic acids. Because of their relatively small molecular size, fulvic acids can easily enter plant roots, stems, and leaves, transporting trace minerals directly to metabolic sites in plant cells. As mentioned, these three humic-substance categories are largely functional in nature: scientists have had a difficult time classifying them based on identifiable physical structure (chemical formulae) because the structures always vary depending on the original organic source, the conditions of decomposition, and the stage of decomposition. Different samples of substances identified as humic acids, for example, may function quite differently in soil. Benefits of Humic Substances The Humic Products Trade Association 5 has conducted a review of the scientific literature and has approved three primary label claims for agricultural application of humic substances: • Improved root mass and growth • Enhanced nutrient availability and uptake • Higher crop yield and quality How are these benefits accomplished? We'll discuss a few of these mechanisms here: • The presence of carbon-containing humic substances in soil results in electrical processes that cause very small soil particles to attract each other to create a crumb structure in the top soil, which has open spaces that allow gaseous exchange with the atmosphere and better water infiltration. This resulting soil structure also increases the water-holding capacity of soil, protecting plants during times of drought. • Energy stored within the carbon bonds of humic substances represents an excellent food source for soil microorganisms that perform a wide range of functions that contribute to soil and plant health—everything from solubilization of minerals that are bound up in the soil to releasing antibiotics that protect plants from pests. • Humic substances have an insulating property that helps to stabilize soil temperatures and slow the rate of water evaporation, which protects plants during change periods of heat and cold. • Humic substances can also stabilize or inactivate certain soil enzymes released by plant pathogens, rendering them less able to damage plants. • Further, humic substances can buffer soil pH, making the soil less alkaline or less acidic. This results in helping trace elements that may have been bound up in the soil due to acidic or alkaline conditions to now become available to the plants as nutrients. • Additional soil benefits are that toxins left in the soil from pesticides can be degraded or inactivated by humic acids, and the addition of humic substances to soils containing excessive salt can help reduce the salt concentration, making the soil more suitable for plant growth. • Humic substances help regulate the retention and release of plant nutrients. The higher cation exchange capacity (CEC) that occurs when humic substances are present in soil increases a soil's ability to retain positively charged plant nutrients (e.g., NH 4 + , Mg 2+ , Ca 2+ , and Na + ) and reduces the potential for leaching. Soil CEC also influences the application rates of lime and herbicides required for maximum effectiveness. 6 • When adequate levels of humic substances are present in soil, plants have an enhanced ability to take up

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