Humus, Humic Acid and Fulvic Acid
Humus is defined as the organic matter in soil, a mixture of partially and totally humified substances. Compost is an intermediate product consisting of humic substances and partially decomposed organic matter.
The use of numerous names to describe commercially available humic materials has contributed to the confusion. Humates, humic acid, leonardite, brown coal, lignite, slack lignite, oxidized lig- nite, weathered lignite, humalite, fulvic acid, fulvates, ulmic acid, humic shale, carbonaceous shale, colloidal minerals, humin, concentrated humus, soil organic matter, peat, humus acid, humus coal and dead organic matter are some of the terms that are used to describe and/or market humic substances.
Potassium hydroxide is the typical alkali used by manufacturers to extract humic acid from leonardite. Since the remaining liquid solution is very alkaline, in the range of 8 to 12 pH, it is incompatible with acids. Here lies some of the confusion, the humic acid synthesized by this operation is not actually an acid. Because it can also be described as the product of adding acid to an alkaline solution, it is a salt — therefore the word “humate” may be more appropriate.
Some manufacturers follow the traditional method described above by treating the alkaline extract with acid, precipitating out the humic acid portion, leaving behind the so-called fulvic acid fraction in solution. The fulvic fraction is acidic, with a distinctive yellowish tint. Note, however, that the operation is vague. There is no definite pH at which the precipitate and acid are separated.
As various fractions of humic substances are soluble in a wide pH range, it makes sense that some fractions must be soluble at neutral pH. Some manufacturers treat humic materials with water, extracting the water-soluble fraction, calling that fraction either fulvic acid or “colloidal minerals,” which are promoted in human neutraceutical markets. Fulvic acid can be operationally defined as “the fraction of humic substances that is soluble in water under all pH conditions.”
The marketing of humic substances is interesting in that there is a lack of standardized analysis within the industry for fulvic acid and humic acid. For example, if liquidized humic materials are subjected to analysis, it is difficult to determine what the analysis reveals because of the infinite number of reassociations of free radicals that are possible during the extraction process. Some scientists argue that the reaction products are substances created by alkali treatment as complex degradation products, stripped of many of the original functional groups and recombined into an indescribable material. This may seem to be a nit pick, but some scientists like to argue about it.
The humin fraction gets very little attention. It may seem somewhat inert, but it has been described as acting like a sponge, soaking up nutrients. M.H.B. Hayes and C.L. Graham report in “Procedures for the Isolation and Fractation of Humic Substances” that the composition of humin is the same as humic acid and fulvic acid. They say that humin may be a humic substance in association with mineral oxides or hydroxides (from the reaction), or that humin may be coated with hydrocarbons or lipids (fats) stripped during the reaction, making them insoluble to aqueous solvents. Nobody really knows for sure.
Some people think that fulvic acid is more biologically active than humic acid because of its smaller molecular size. There is some truth in these representations as there is evidence that the lower molecular weight fractions have the ability to cross plant membranes and improve permeability of cell walls. It is true that fulvic acids have a higher “total acidity” than humic acids, but the chemical reactivity and chelating ability of humic acids is equal to or greater than fulvic acid, making them very bioactive substances. The humic acid fraction may be more effective than fulvic acid at solubilizing extremely stable aluminum and iron phosphates.
Carbon nuclear magnetic resonance and mass spectrometric analyses have revealed that the main structural features of humic acid, fulvic acid and humin are nearly identical. To scientists who study humic substances, the names have no meaning chemically. Some scientists say that humic substances from different sources are essentially the same.
Reported variations in plant response to different sources of humic substances are rare. In one case reviewed by Y Chen and T. Aviad in “Effects of Humic Substances on Plant Growth,” the young age of the humic materials were suspect, because humification is a time-dependent process. As the material ages, more bioactive ingredients become incorporated into the humic complex.
COMPLEX GEOBIOLOGICAL SYSTEMS
The lower molecular weight (the mass of a substance expressed in gram equivalents of its atomic mass) of fulvic acid is sometimes said to account for its greater biological availability. That is somewhat correct, but vague — the industry has not agreed on standardized molecular weights for fulvic acid. Defining humic acid, fulvic acid and humin by their molecular weights is a controversial concept.
Humic substances change their structure depending on pH and the type of metals present. High pH (or the presence of multivalent ions, such as calcium Ca +) makes humic substances open up their long-chain polymers, whereas low pH makes them close. In the presence of toxic metals, humic substances remove the metals from the surrounding environment by forming insoluble aggregated spheres around them.
Humic substances are polymer-like molecules that demonstrate self-organization. The bi-layers formed by humic substances to surround otherwise insoluble minerals are reminiscent of the way all living things utilize biochemical reactions. The self-organized (micellular) colloidal phases act like biological molecules in cellular systems, showing a strong resemblance to the biological mechanisms of living membranes, as described in college textbooks. Humic substances are more like living creatures than chemical entities, but they don’t reproduce.
Slight changes in pH will actually cause the humic polymers to fracture, breaking up the original molecules. The fractured molecules are then free to associate with numerous other free radicals, metals or impurities. Humic substances are made up of hundreds of different molecules of many different sizes (polydispersity) with many ways to orient them-selves by twisting, bending, compressing, and expanding (conformational changes). They are held together loosely by weak forces in a colloidal state.
Any change in solution pH, concentration or the presence of metal ions — especially calcium ions — will cause huge changes in the physical makeup of the humic molecules. Even slight changes cause the molecules to change in orders of magnitude. Rapid changes in molecular structures are not unique to humic sub- stances — water molecules, for example, change their structure 10 trillion times a second. Although water is an extremely simple molecule, the determination of its structure at any given instant is still not fully known. The amazing complexity of humic substances may forever keep their structures a secret.
FULVIC ACID
The primary reason why there is so much confusion about humic substances is the fact that the procedures used to describe them are based on “classical” aqueous extraction. If minerals are present in the parent material, they become complexed by humic substances. This allows more humic and non-humic material to be solubilized during extraction by breaking down ion bridges that would normally hold the molecules together in higher-purity materials. Unless the super- natant is separated by special procedures (such as passing over an XAD-8 resin) to isolate the fulvic portion, the extracted substances may contain amino acids, proteins, sugars or fatty acids in addition to the fulvic acid.
In biological molecules, it is an established fact that the presence of functional
groups such as carboxyl, phenol, quinone and hydroxyl are responsible for the activity of these molecules. There is some evidence that there are more functional groups in fulvic than in humic acid. The effectiveness of fulvic extracts may be influenced by the way they are synthesized during chemical processing. The fulvic fraction of humic substances is undoubtedly a beneficial part of oxidied lignites.
