Most gardeners know the value of adding compost for growing a healthy garden. Compost, the decomposed remains of plants, animals and their byproducts, provide many of the raw materials for vigorous plant growth. Humic acid is extracted from prehistoric compost piles. Although much of the fertilizer value of the compost has long been leached away, the biostimulant value still remains. Humic acids consist of two parts, humic acid and fulvic acid. Humic and fulvic acids actively help the plant take up nutrient ions that are often locked up in the soil. The extracts, obtained from leonardite, also contain many beneficial trace elements that activate important enzymes in the plant.
The greatest value of humic and fulvic acids are their roles as chelators. “Chela” is a Greek word meaning “claw”. Humic and fulvic acids have functional groups that act as claws, holding mineral ions strongly enough to keep them from reacting with each other and becoming unavailable to the plant, but weakly enough so that they can be released to the plant cells on demand. The humic acid fraction consists of large organic molecules, acting as a sink for important cations such as potassium. Humic acid transports the minerals to the outside of the cell membranes, and releases the minerals for uptake by the plant. The fulvic acid fraction consists of small organic molecules that easily penetrate cell membranes. The more biologically active of the two fractions, fulvic acid transports minerals through the cell membranes and releases them directly to the plant cells.
Humic acids are even more effective when used in conjunction with seaweed extracts. Such interactions have a “synergistic effect”, meaning that they work better when used together than when used separately. According to a ten-year study on biostimulants conducted by Virginia Tech, humic acids and seaweed extracts, when used together in a 5:2 ratio, work 50% more effectively than either product used alone. The seaweed component, rich in plant growth hormones, signals the plant to grow. The humic acid component, with its chelating effect, amplifies the signal of the hormones. The results? Greater root mass, faster growth, and improved stress resistance.
One of the most interesting discoveries from the Virginia Tech study was the effect of the humic acids and seaweed extracts as plant protection agents. The combination was proven to stimulate the production of an enzyme called superoxide dismutase (SOD). Superoxide is a very destructive “free radical” that attacks and oxidizes cell membranes, but SOD breaks down the superoxide molecule into a form less destructive to plants. SOD protects the cell walls, allowing better uptake of water and nutrients. SOD also protects the chloroplast and mitochondrial membranes, allowing better utilization of light from photosynthesis and better energy production from cellular metabolism. Under normal conditions, the plant produces enough superoxide dismutase to protect itself, but under stress conditions, such as UV, heat, drought or salt stress, free radicals build up that destroy plant cell membranes. The extra levels of SOD and other antioxidants stimulated by the seaweed/humic acid combination conditions the plant to quickly recover and remain growing under sub-optimal conditions.
Many enzymes are activated by metal ions called co-factors. The most important essential trace elements that act as cofactors are iron, manganese, copper and zinc. Hundreds of cellular enzymes remain inactive unless turned on by these inorganic cofactors. For example, superoxide dismutase needs metallic cofactors in order to actively protect the plant, either an iron/manganese complex or a copper/zinc complex. Many other crucial chemical reactions are activated by metallic cofactors, without which the plant would weaken or die. The chelating effects of humic and fulvic acids greatly improve the availability of these essential trace elements when they are needed most.
Both seaweed extracts and humic acids contribute many beneficial trace elements to the plant. More than 60 trace elements have been identified in humic acid and seaweed extracts, along with the chelating agents that make them readily available to the plant. In hydroponics, all of the “essential” trace elements are added to the nutrient formula, usually with strong, synthetic chelators such as EDTA or DTPA. “Beneficial” trace elements found in humic acid/seaweed, though not essential for plant growth, have positive effects on plant growth and vigor, and help the plant attain its full genetic potential. Although given to the plant in very small amounts, usually in parts per million or even parts per billion, beneficial trace elements can stimulate plant growth and provide extra protection against pathogens. For example, silicon is not an essential element, but it helps strengthen leaf cells against fungal attack and improves the permeability of root cells to water and minerals. Cobalt is a part of vitamin B12, essential to nitrogen-fixing rhizobacteria. Iodide is sometimes added to plant tissue culture media to stimulate rapid cell growth, and other beneficial elements are being discovered by plant biologists every year. In addition, many beneficial elements are known to accumulate in plant cells, and though they are not essential to the plants, they are essential to the animals that eat them! Therefore, the judicious use of humic and fulvic acids may contribute to the nutritional value of fruits and vegetables, both directly through the addition of beneficial trace elements, and indirectly by improving the plant’s ability to take up and utilize both essential and beneficial elements.