Humic acid is a principal component of naturally occurring humic substances contained in particular soils. These organic compounds are major constituents of various soil/humus types, such as peat, coal, stream bed sediment, dystrophic lakes, and ancient sea beds. Humic substances are produced by the bio-degradation of dead organic matter, making them water soluble and naturally present in various soil types.
Humic acid is the commercial term often used to refer to the combined humic, fulvic and ulmic acid content found in these ancient organic soil deposits. Humic acid is known to be among the most bio-chemically active materials found in soils. And because of their wide ranging agricultural benefits, humates, as they are broadly referred to, are universally recognized for their effectiveness as a growth enhancing soil supplement.
The fulvic component of humic acid is distinguished by its lower molecular weight and higher oxygen content than the other humic constituents, and therefore plays a key role in facilitating nutrient uptake.
Humic acids are not a single compound, but rather a composite of different molecular weight complexes with similar characteristics. They are usually defined by the process through which they are isolated and extracted, rather than by a particular chemical structure. Among other characteristics, these organic acids provide an excellent source of soil amending carbon. These complex organic acids occur naturally as an amalgam of numerous different acids containing carboxyl and phenolate groups, so the mixture behaves functionally as a dibasic or tribasic acid. Humic acids can also form complexes with ions that are commonly found in the environment, which then form humic colloids. These acidic compounds usually contain carbon, hydrogen, oxygen and nitrogen, with small amounts of sulfur and phosphorus.
Premium grade humic acids used by expert gardeners are most often extracted from a substance known as Leonardite, a form of carbon/oxidized lignite created over time by fully decomposed plant matter. Leonardite is the preferred source of humates because of the high concentration and potency of the humic matter it contains.
Humic acid in its refined form is a dark brown, even blackish, organic bio-stimulant with natural chelation properties. Fulvic acid is created and extracted from the same sources and therefore shares these same properties, but is a short-chain molecule which is yellow, golden in color – both acids are fully soluble. In horticulture it is the humic, and particularly the fulvic acids, which are most reactive and effective in stimulating plant growth.
The Value of Humic Acid in Gardening
Modern chemistry and agronomics has recognized the exceptional value of humic acids for their beneficial impact on plant growth and crop yields. Nutrient and organically-deficient soils such as silt, sand and clay are greatly improved by the addition of humates because of their carbon, hydrogen, oxygen and nitrogen content, and water retention properties. However, it should be understood that humic acid of itself is not by strict definition a fertilizer, as it does not directly provide nutrients to plants; but rather, it is a compliment to fertilizers in that it makes the nutrient components of fertilizers more usable to plants and increases the uptake amounts of those nutrients.
Of special interest to urban gardeners is the function of these organic acids as natural chelators. Humic and fulvic acids contain carboxyl and phenol groups that chelate, or bind, unstable metal ions into stable organic-mineral complexes. Some of these metals are then made more available for root/plant uptake because they are kept in a soluble chelated form. The molecular activity stimulated by soil humates positively affects mineral exchange reactions, which in turn has profound beneficial effects on soils and plant growth.
Some important benefits of humic acids include:
- Increased root vitality
- Increased nutrient uptake
- Increased fertilizer retention
- Increased chlorophyll synthesis
- Healthier plants and improved yields
- Stimulate beneficial microbial activity
Humic Acid and Soil Enhancement
Humic acid can soften and help break up compacted soils, allowing for improved water penetration, aeration and better root zone health, growth and development. When applied to sandy soils, humic acid adds essential organic material necessary for water retention, thus improving root growth and enhancing the sandy soil’s ability to retain, rather than leach out vital plant nutrients. Humates also participate in the decomposition of rocks and minerals in soils.
Humic Acid and Improved Plant Growth
As stated in the previous paragraph, one way plant growth is enhanced by humates is through the structural improvement of nutrient deficient soils, especially clay and sandy soil types. This amended soil composition creates conditions for improved root development.
Additionally, humic acids are known to not only promote microbial growth and colonization, but also to aid in the conversions of a number of elements into the plant available form, which consequently has a stimulatory effect on plant growth. Moreover, humic and fulvic acids have been widely proven to increase the rate of development and length of root systems, and also to accelerate cell division. This results in thicker cell walls, stronger plant stems and increased foliage.
But among the foremost benefits of humic acids is their ability to significantly increase the nutrient uptake by plant root zones. Humic acids accomplish this by freeing up nutrients in the grow media and converting them into easily assimilated forms so they are made available to the plant as needed. For example, if an aluminum molecule is joined with a phosphorus one, humic acid has the unique ability to separate the molecules, which then makes the phosphorus readily available to the plant. Humic acid is also especially important because of its ability to chelate micronutrients, thus increasing their bio-availability.
Humic Acid and Microbial Activity
The activities of beneficial soil microbes are crucial for the sustainability of soils and the efficacy of soil-less grow media. When present in soils, humic acid stimulates microbial activity by providing the indigenous and beneficial microbes with a carbon source for food, thus encouraging their growth and activity. Soil microbes are responsible for solubilizing vital nutrients such as phosphorus that can then be absorbed by the humic acid and in turn made available to plants. Additionally, microbes are responsible for the ongoing development of humus in the soil as they continuously work at breaking down partially decomposed organic matter. This natural production of humus then continues to add to the humic acid base and its benefits.
Nutrient Fertilizer Enhancement & Utilization
In technical terms, humic acid is not a fertilizer; but rather, it is a highly effective agent used as a complement to synthetic and organic fertilizers. The role played by humic acid in increasing nutrient uptake by means of its chelation properties reduces the amount of fertilization needed due to the root systems enhanced ability to utilize the existing nutrients already present in the grow medium. In certain conditions, fertilization can be eliminated entirely if sufficient organic material is present and allows the soil to become self-sustaining through microbial processes and humus production.
Humic Acids as Bio-Stimulants and Root Growth Promoters
As a bio-stimulant, humic acid also promotes hormonal activity in plants. Plant hormones are chemical communicators/agents, which help regulate plant development and responses to environmental conditions such as temperature and water availability. The bio-stimulant characteristics of humic acids also promote antioxidant production in plants which, in turn, reduces free radicals. Free radical molecules result from stress brought on by drought, heat, ultraviolet light, herbicides, etc. Free radicals are harmful because they are strong oxidizing agents which damage lipids, proteins and DNA within plant cells. Antioxidants, in contrast, are metabolites and enzymes which seek out and neutralize free radical molecules, thus protecting plants from their damaging effects. They include lipid soluble substances like vitamin E, beta-carotene, and water soluble materials such as vitamin C and various enzymes.
Humic Acid Functions Summarized
- Unique natural chelation properties
- Promotes and facilitates nutrient uptake
- Stimulates plant enzymes and hormones
- Promotes protective antioxidant activity
- Suppresses disease and root zone pathogens
- Improves soil fertility and microbial activity
- Increases microbial and mycorrhizal activity
- Effective soil enhancer for improved soil structure
- Increased chlorophyll synthesis and healthier foliage
- Plant growth bio-stimulant of important plant functions
- Stimulates root function and growth, increasing nutrient uptake
- Reduces fertilizer requirements and increases yields in most crops
- Stimulates overall plant growth and biomass development by accelerating cell division for thicker cells walls in fruit and vegetables; resulting in prolonged storage and shelf life, with improved appearance of crop and higher yields