Fulvic acids. Structure, composition and formation of fulvic acids
Fulvokisloty (FK)is a mixture of weak organic acids of the aliphatic and aromatic series, which are soluble in water at all pHs (acidic, neutral and alkaline). Their composition and form are very variable. The molecular weight of the FK (1,000 - 10,000) is less than that of the HA, and the oxygen content is twice as high. Because of the relatively small size, the PK molecules can easily penetrate the roots of the plant, stems and leaves, bringing in useful micronutrients. Fertilizers used in the form of aerosols and containing FC in the form of chelates with microelements, at certain stages of plant growth can be an effective means of increasing its productivity. When foliar treatment of plants FC deliver trace elements to the metabolic sites of cells. They are compatible with the plant and thus are not phytotoxic when applied at relatively low concentrations.
Some researchers consider fulvic acids to be the most important part of the organic matter of the soil. However, their high solubility in water casts doubt on the possibility of their long existence in natural objects (excluding groundwater). Moreover, it has been established that enzymes that carry out carbohydrate, nitrogen and phosphorus metabolism are firmly bound to humic acids and are released from the soil together with them, while retaining activity. It is with humic acids that the main part of hydrolytic enzymes is bound. So invertase activity in the presence of humic acids is 5-6 times, urease is 3.5 times, protease is 1.5 times higher than in fulvic acids.
Not so long ago D. Orlov published a work that makes it necessary to consider this problem in a new way. He came to the conclusion that in the natural objects - soil, coal, peat and other sources of humic substances - fulvic acids generally do not exist as an independent fraction. Those FK, which we define as part of the humic substances that pass into the solution when processing the object (lignite, peat, soil) with alkalis and remaining in it after acidification of the solution to pH 2 for the precipitation of humic acids, are formed in solution as a result of analytical procedures that cause a partial hydrolysis of high-molecular humic acids .
Practically all the experimental data indicate that FCs appear only after alkaline or acid hydrolysis of the organic matter of the investigated objects as a whole, and humic acids in particular. Consequently, the analytically determined content of fulvic acids indicates only one or another degree of hydrolysability of natural humic acids, regardless of the object of their production.
Further studies by O.Yakimenko and F.V. Ulankina also lead to the conclusion that the effect of hydrolysis of humic acids during alkaline extraction can not be ruled out on the formation of fulvic acids.
Thus, the role of FC can be considered only in cases when we use humic preparations obtained by treating lignite or peat with alkaline agents, since only after such treatment a mixture of humates and fulvates of alkali metals appears in these products.
In addition, we have as yet unpublished data from two independent studies conducted by GA Kalabin and O.S. Yakimenko on fragments of corn coleoptiles, which showed that the growth-stimulating activity of fulvic acids is manifested only in combination with the fraction of humic acids . The use of the fulvic acid fraction in its pure form, according to their data, does not lead to stimulation, but to inhibition of growth.
Therefore, discussing the mechanism of the effect of humic substances on plants, in the future we will operate with the concept of humic acid, suggesting that FCs are an integral part of it.
In addition to the soil, humic acids are found in large quantities in brown coals, peat, sapropel and some other organic substances.
In the soil, humic acids are bound to other cations, mainly Ca, Mg, Fe, Al. Therefore, they are practically insoluble in water, which allows them to accumulate, forming certain reserves of humus, and then very slowly, as mineralization and consumption by microorganisms, serve as a source of nutrients, growth stimulants, enzymes, vitamins and many other biologically active substances necessary for growth and plant development.
In order for humus substances to become available to plants, they must go into a water-soluble form. This process occurs in the presence of alkali metals and some other elements and compounds to form water-soluble salts - humates.
HumatesAre salts of natural humic acids in which the hydrogen ion of carboxyl and (partially) hydroxyl groups is replaced by a metal atom. Natural humates are formed in the soil as a result of the interaction of humic acids with the ions of the metals of the soil solution in the form of insoluble salts. They determine its genetic, ecological and agronomic functions. In natural objects called caustobioliths - brown coal, peat, sapropel and some types of shale - they are contained in fairly large quantities and serve as a raw material for the production of water-soluble humates of alkaline metals - sodium or potassium humates. Of all the humates, only the humates of potassium, sodium and ammonium are water-soluble. These humates show all the positive properties of soil humic substances, but, due to their high solubility in water,
In the future, using the term "humates", we will bear in mind precisely the water-soluble humates of potassium, sodium or ammonium.
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