Humic substances in the environment perform several important functions:
- prolonged accumulation of nutrients and trace elements necessary for growth;
- improve nutrient circulation in the living organism (both plant and animal);
- regulate plant nutrient and water uptake;
- protect from adverse environmental factors and strengthen plant and animal immunity;
- improve the productivity of photosynthesis and increase the chlorophyll content in plants, resulting in increased productivity and plant resistance;
- efficiently absorb toxic heavy metals and ensure their excretion from the body, thus acting as bioregulators.
Humic and fulvic acids intensify the absorption of oxygen in plant cells, stimulate formation of the root system, increase cell membrane permeability, activate enzymes, improve plant respiration. The more intense the plant respiration is, the plant is healthier and able to produce more biologically active substances such as vitamins, amino acids, etc.
Humic acid structure, mechanism of action and application in agriculture
Humic acid salts = accelerated growth and stronger root system
The importance of humates in agriculture is already known from the history. However, the change from the general level of understanding to scientific understanding took place only at the beginning of the last century, when the isolated humic sample in the form of soluble sodium salts was used for planting. This experiment was carried out in the middle of the last century by a young scientist from Ukraine, Lydia Khristeva, who, with a sample of hydrolyzed humic salts, watered plants and this resulted in markedly accelerated growth and a stronger root system. This simple experiment has shown that by converting natural humic substances in the form of sodium (or potassium) salts more than one hundred times increases their biological efficiency.
Further we will briefly explain the effect of humic substances on the system responsible for yield – water, plants and soil.
Below depicted is a molecule of humic acid.
Electron capture = resistance to stress
This is a quinone group where you can see 4 simple and 4 double carbon bonds. In nature, this molecule is a cloud of electrons, where electrons are at a certain level of valence. By receiving a solar energy quantum, the electrons move at a higher energy level, which ensures the accumulation of solar energy. At night, these electrons return to their previous positions, supplying the cell with energy. In this way, humates influence the cell’s energy balance.
In nature, it is manifested in the development of an active development of root system and synthesis of specific enzymes. These enzymes increase plant resistance to stress factors (frost, drought).
Humic acid salts – soluble in water = available for the plant
The peptide group is structurally similar to the lipid structure of cell membrane. In this way, this group can interact with the cell and form a protective membrane around it. During growth and development, the cell is always exposed to stress, such as peroxide, toxins, free radicals and other factors. Studies have shown that 30% of cell energy is used to protect the cell. The protective membrane made of humates performs this protective function by allowing the cell to use available energy for growth and development only.
The group of carbohydrates or sugars, like the peptide group, is a good source of nutrients for microorganisms.
In the side of the molecule there is carboxyl (COOH) and hydroxyl (OH) groups, which perform several important functions. First of all, these groups have an affinity for water, which means humic acid molecules are water soluble. Diluted humic acids change the structure of the water, giving them the melted water structure. Such water is structurally very similar to water in the cell, therefore it can easily enter the plant cell and become part of the plant development process. For this reason, we recommend the use of humate dilutions in the range of from 0.008 to 0.01% for application on leaves. Second, the hydrogen atoms contained in this group may be replaced by metal ions. This happens as follows:
During dissociation, K + or Na + enters the water phase, but humate ions acquire a negative charge. In the presence of negative charges, the humate molecule unfolds, forming a long chain and thus obtaining biological activity. This is the reason why we recommend using humic acid salts instead of pure humic acids contained in lignites, such as leonardite.
Soluble salts – for transportation of trace elements in a cell, insoluble – for contamination binding
Calcium and magnesium humates are insoluble in water, unlike sodium and potassium humates.
Humic acids also will interact with multivalent metals such as iron, zinc, copper and others, whereupon they form other types of compounds called chelates, one of the types of complex compounds. The scientific explanation says: complex compounds are neutral molecules or electrically charged ions formed by joining a central atom to other molecules or ions called ligands. Chelates are complex compounds whose ligands are linked to a central atom via two or more atoms. In addition to the usual bonds, they form coordination bonds. The coordination (semipolar, donor-acceptor) bond is a kind of covalent bond formed between atoms that form different molecules, one of which has an unbound electron pair, and the other does not have two electrons to form a stable external electron shell. Such links are typical of complex connections.
The chelates under normal conditions are insoluble in water, but under certain conditions they are water soluble, which allows to manipulate their solubility. On the one hand, we can supply plants with the metal ions they need – iron, copper, zinc, boron, magnesium, molybdenum and cobalt in their soluble forms, and on the other hand we can protect plants from harmful elements such as mercury, lead, cadmium, radionuclides and others by binding them and thus making insoluble. Humates, therefore, are important both as transporter of valuable trace elements and as binders of contaminants. Satellite photos show that the environment in humate rich regions is environmentally balanced, despite the intensive industry.
Humic substances attract moisture
Due to the high degree of hydrophilicity of humic colloidal structures and their functional groups, they are capable of forming gels. It can explain the effect of humic substances on increasing soil moisture absorption capacity. This fact is very important for dry regions.
Water, through hydrogen bonding, closely interacts with humic acid molecules and allows to maintain soil moisture in dry weather conditions.
Humic substances promote the development of soil microbes
When reacting with calcium, magnesium, aluminum and iron, which is always in the soil, humates form organomineral bridges, combining soil particles that prevent erosion, allow oxygen and moisture to be maintained, and also create a favorable environment for the development of soil microflora. Literature has repeatedly indicated that active soil microorganisms are a key factor in the production of humates.
Humic salts – a soil stimulant and a nutrient vehicle
It is important to emphasize that humic acid salts are not a significant source of nutrients but are soil stimulants and a vehicle for feeding nutrients into plants. By joining a humic acid molecule, nutrients are transported to the plant in available forms and thus help to accelerate plant metabolism.
Humic acid salts increase the effect of fertilizers and pesticides
When used together with mineral fertilizers or pesticides, the presence of humates makes these compounds more effective. In most cases, the use of systemic pesticides can be reduced by 25% or more when used together with humates. Total nitrogen may be reduced by 30% or more if humates are used in accordance with the manufacturer’s instructions. Humates are compatible with all types of fertilization programs, except for products with very low pH. In laboratory tests, precipitation was not observed with materials with a pH above 3. Due to safety reasons, small quantities of our products may be mixed with fertilizers prior to use, to ensure that no residues are present for use at a pH lower than 4.
In order to be biologically active humates should be converted into salts!
Although described above is just a small part of the information on the role and effects of humates on the aquatic, soil-plant system, it gives a basic understanding of these unique compounds. In conclusion, it should be emphasized that humic acids in their natural state that the component of peat or lignite is always linked as insoluble forms of calcium, magnesium or aluminum, and therefore are also of little biological significance. The recommended dose of such products is close to 1000 kg per 0.5 hectare, which is neither practical nor economical. These products should be converted into soluble humates, chelates or pure humic acids to make them biologically active, because only in that way they will be able to provide the above described contribution to agriculture.
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2. Freeman, PG. (1965). The use of lignite products as plant growth stimulants. Technology and use of lignite, IC Bureau of Mines Information Circular, 8471: 150-164.
3. Levinsky, B. (1999). Everything about humates. Irkutsk University, Siberia, 1-23.
4. Senn, TL and Kingman, AR (1973). A review of humus and humic acids. Clemson University. University of Horticulture, Research series No. 145.