The effect of physiologically active humic acids on plants under unfavorable external conditions
The stimulating effect of physiologically active forms of humic acids can be considered a firmly established fact; however, the degree of its manifestation is far from stable. It was noticed as early as the Soviet era that the effect of applying these substances is always relatively higher when external conditions deviate from the norm. Many other researchers came to the same conclusion independently of us.
It is obvious that the study of these conditions has not only theoretical but also practical significance, as it allows for the differentiation of areas and methods for the most effective use of physiologically active forms in agriculture.
However, the most complete solution to this problem will be possible when the biological mechanisms of interaction between physiologically active forms and the subcellular structures and functions of the organism itself are uncovered. Therefore, we will consider the available experimental material from these two perspectives.
Effectiveness of PAH Depending on Plant Mineral Nutrition Conditions
Mineral nutrition is one of the most studied and most regulated-by-human-will factors of the external environment. Without delving into the history of this issue, we note that at the current stage of agricultural development for all technically developed countries, the most important task is to increase the utilization efficiency of mineral fertilizers, especially nitrogen fertilizers, since a direct increase in doses above a certain limit yields no effect.
The works of several authors demonstrating the potential for using physiologically active substances of a humic nature for these purposes are also of undeniable interest. In addition, it is important to know under what mineral nutrition conditions the physiologically active forms are most effective.
Soviet scientists began to address this issue in the late 40s and early 50s. Based on these studies, they concluded that "a certain connection exists between mineral nutrition and the stimulating influence of humic and fulvic acids. It is expressed in the fact that humic acid, thanks to its physiologically active properties, promotes more complete use of mineral food, especially when mineral nutrition conditions deviate from the norm."
As an example confirming the above, we present in Table 1 the results of one of our experiments, which confirmed that the **effectiveness of humate was especially noticeable against a background of nitrogen excess and phosphorus deficiency**.
| Experiment Scheme, Ratio | Applied after 15 days | Weight of spring wheat plants, 30 days | ||
|---|---|---|---|---|
| Without K-humate, In % of 1 N : 1 P | With K-humate, In % of 1 N : 1 P | in % of its control (without humate №) | ||
| 1N : 1P | 100 | 99 | 99 | |
| 1N : ¼ P | + ¾ P | 53 | 111 | 192 |
| ¼N : 1P | + ¾ N | 81 | 79 | 98 |
| ЗN : 1/4P | + ¾ P | 76 | 129 | 158 |
P of the experiment = 1.01%.
However, there were no lethal doses of nitrogen here, so we later set the goal of finding out whether it is possible to increase the resistance of plants to high doses of nitrogen by affecting seeds and the primary growth phases of seedlings with physiologically active forms. In this experiment, corn seeds were first germinated on potassium humate and water (control) until they were two weeks old, then transplanted onto Pryanishnikov's mixture with different amounts of nitrogen (water cultures, phosphorus was given as Sorensen's mixture). 7 days after transplantation, the experiment was recorded by the root test — Table 2.
| Nitrogen norm in Pryanishnikov's mixture, onto which two-week-old seedlings were transplanted | Medium for seed germination and seedling production | Primary roots | ||
|---|---|---|---|---|
| 1st order | Average length of 2nd order, MM | |||
| Average length, mm | Quantity per plant | |||
| 1 | water | 9.4 | 34 | 13 |
| 1 | 0.0025% potassium humate solution | 12.0 | 71 | 19 |
| 4 | water | 11.7 | 24 | 4 |
| 4 | 0.0025% potassium humate solution | 12.7 | 54 | 14 |
| 8 | water | 8.2 | 20 | 4 |
| 8 | 0.0025% potassium humate solution | 11.1 | 44 | 10 |
Table 2 shows that the effect of potassium humate was positive on all nitrogen nutrition backgrounds, but it is especially important that the preliminary cultivation of seedlings on potassium humate increased their resistance even to nitrogen concentrations such as N 8, which were clearly lethal.
Field experiments with rice were conducted at our laboratory, which showed that the presence of physiologically active forms and other organic substances in the fertilizer composition increases the effectiveness of high doses of nitrogen and removes its negative effect in the natural environment (Table 3).
| Experiment Scheme | Background N60P100 | Background N120P100 | Background N160P100 | |||
|---|---|---|---|---|---|---|
| Increase cwt/ha | % | Increase cwt/ha | % | Increase cwt/ha | % | |
| Control (background) | (37.2) | — | (52.0) | — | (59.7) | — |
| Background + N60P90K20 in Imperium Agro.Bio | 6.2 | 16.6 | 6.8 | 13.1 | 3.5 | 5.9 |
| Background + N60P90K20 in mineral fertilizers. | 5.1 | 13.7 | 2.3 | 4.4 | -3.2 | —5.3 |
P of the experiment = 2.3%.
The increased effectiveness of mineral fertilizers with the parallel use of physiologically active forms of a humic nature has also been noted in a number of works by our scientists. Numerous works by other researchers also attest to this.
In experiments with millet and oats in sand cultures on Brikha's mixture containing $KN1503$, they proved that the addition of humic and fulvic acid solutions to the nutrient medium not only positively affected the assimilation of K15 but also contributed to better utilization of the nitrogen contained in the humic and fulvic acids themselves. In world practice, striving to differentiate the plant response to mineral and organic fertilizers, experiments were set up in vegetation vessels with various humus substances, such as: manure, fermented straw or peat, isolated humates, and others, against a background of applying mineral salts in different doses. In an experiment with ryegrass, he showed that the plant response curves to different nitrogen doses are related to the level of phosphorus nutrition (Fig. 1).
- However, when the dose of both nitrogen and phosphorus increases, a "ceiling" in their action occurs.
- A further increase in nitrogen and phosphorus even leads to plant suppression.
- The application of humic substances against such a background significantly shifts this "ceiling."
His experiments also clearly showed the influence of humic substances on the removal of nutrients. As an example, Table 4 presents the results of experiments with rye.
We explained the conflicting data on this issue obtained by other authors, on the one hand, by the different methodology of the experiment, and on the other, by the effect of "dilution" of the received substances by the crop mass. Fig. 2 is no less interesting, where data from another vegetation experiment with ryegrass are presented.
| Quantity of each element applied per 1 kg of soil (NPK), g | N | P2O5 | K2O | |||
|---|---|---|---|---|---|---|
| without humus | with humus | without humus | with humus | without humus | with humus | |
| 5 | 0.5 | 0.7 | 0.4 | 0.6 | 29.3 | 28.9 |
| 10 | 0.5 | 1.0 | 0.5 | 4.1 | 30.0 | 35.4 |
| 20 | 2.9 | 3.2 | 3.0 | 3.7 | 31.9 | 36.1 |
| 30 | 4.5 | 5.7 | 1.7 | 4.6 | 34.3 | 35.9 |
| 40 | 4.2 | 9.2 | 4.2 | 5.1 | 35.3 | 42.3 |
In this experiment, against the background of sufficient supply of all nutrients to the plant, the nitrogen dose was varied. It turned out that the highest yield was obtained when it was applied at a rate of 27 mg/l; after that, the yield curve showed a slight plateau and then dropped.
The application of 2.5 mg/l of potassium humates from leonardite sharply changed the picture:
- The negative effect of high nitrogen doses disappeared.
- As their doses increased, the yield of ryegrass increased, although disproportionately.
- Scientists emphasize that this process is also accompanied by better utilization of the absorbed nitrogen within the plant itself, as a greater amount of dry matter is formed per unit of nitrogen.
The difference between this work and previous ones is that we tested different doses of NPK in hydroponics on quartz against a background of varying doses of physiologically active humic substances. In the experiment with corn, he obtained clear results showing that physiologically active humates alleviate the toxicity of high NPK doses, and this effect is well manifested at humate doses of 6, 24, and 96 mg/l (Figs. 4 and 5). The scatter of humate doses in terms of effectiveness is explained by the fact that the physiological action of these substances is based on two principles:
- **Quinoid and polyphenolic groups:** are part of the humic and fulvic acid molecule, which activate the oxidoreduction reaction and the transfer of $H_2$ to $O_2$.
- **The second part of the molecule:** is formed by proteins and other chemical groups that, in our opinion, possess enzymatic properties. This part of the molecule, as he believes, influences photosynthesis.
The equilibrium established between the two factors determines their physiological effect on plants; moreover, depending on the dose of humic acid, one side or the other predominates in its action. In our work, we illustrate that humic acids:
- Normalize the uptake of $NO_3$ ions from solutions containing elevated NPK concentrations.
- Have almost no effect on $PO_4$ uptake.
- Alleviate chlorosis that occurs at high NPK doses by balancing the uptake of nitrogen and magnesium.
The optimal dose of humic acids, in our opinion, can only be found by considering the doses of NPK against which it is applied.
The works of Guminski and Guminska are of great interest in this regard, as they showed that fractions of humates or potassium humate without fractionation can be used as protection against high concentrations of the nutrient solution. They managed to confirm under hydroponics conditions that the addition of humates to the medium increases the crop yield by 40% against the normal nutrient mixture on a background of a 4-fold NPK concentration. They emphasize that the nutrient solution at a triple concentration without humate has a negative effect on the solution.
Other Environmental Factors and the Effectiveness of Physiologically Active Substances
Above, we considered the effectiveness of physiologically active forms depending on the ratio and doses of the main mineral elements. But the uptake of nutrients into the plant is affected not only by their forms and presence in the root nutrition medium, but also by:
- osmotic pressure;
- the presence of toxic ions in the soil solution;
- its pH;
- oxygen availability to the roots, and others.
There is reason to believe that physiologically active substances, causing significant shifts in the plant's metabolism, can influence its reaction to these factors as well.
Hernando dedicated one of his works to the use of soluble humates to alleviate toxicosis in plants caused by the salinity of the root nutrition medium. He introduced $CaCl_2$, $NaCl$, and $MgSO_4$ into a normal nutrient solution, raising its concentration to 5.6 and 12.6 Mo conductivity. Against this background, Hernando tested the effect of different doses of humic acids.
From Hernando's work, it follows:
- Humic acid at certain concentrations alleviates the toxic effect of salinity at 5.6 Mo, which inhibits the normal growth of corn.
- The maximum effect of humic acid is manifested at two doses, namely 12 and 120 mg/l.
- Under the influence of humic acid in plants under salinity, the cation ratio is normalized (Fig. 6).
- The optimal dose of humic acids for high salinity (12.5 Mo) is 80 mg/l.
Hernando's main conclusions:
- Humic acid alleviates toxicosis caused by the disturbance of physiological equilibrium in the root nutrition sphere.
- The level of physiologically active humic acid application is not proportional to the resulting effect.
- Calculating organic fertilizers requires more complex approaches than mineral fertilizers.
We present data from a vegetation experiment characterizing the influence of different doses of humic acid on the growth of peas depending on the pH of the medium. This substance was more effective in the case of unfavorable medium reactions ($pH 4$ and $7.5$) and showed a weak effect in the case of a reaction quite suitable for peas ($pH 6$). It should be noted that at all medium reactions, the maximum effect was obtained from the smallest dose of humic acid used in the experiment.
Summarizing his experimental data, Professor Guminski asserts that the law here is: the greater the deviation of the medium reaction from the optimal for a given plant, the more noticeable the effect of the physiological action of humates (referring to pH deviations that do not lead to plant death).
Studying this issue on a tomato test culture, we concluded that the effect of humic substances increases with a lack of oxygen in the root medium. Averaged calculations showed:
- With aeration, the increase in the weight of the aerial mass of water cultures was 35% and roots +44.4%.
- Without aeration, the increase was +36.4% and +267%, respectively.
We present the results of one of our experiments in water culture with corn seedlings, in which humic acids were introduced into the medium against a background of various conditions of mineral and oxygen nutrition (Table 5). The average temperature of this experiment was $30—32°C$.
| Experiment Scheme | With aeration and shaking | Without aeration, with shaking | ||||
|---|---|---|---|---|---|---|
| % of undamaged plants on the 10th day of the experiment | average root length, M±m | number of 2nd order roots per plant | % of undamaged plants on the 10th day of the experiment | average root length 1 M±m | number of 2nd order roots per 1 plant | |
| Full Pryanishnikov's mixture | 62.5 | 115±7.44 | 44.5 | 51.0 | 101±6.27 | 27.0 |
| The same + potassium humate 10 mg per 1 l | 87.5 | 130±6.57 | 87.5 | 72.0 | 122±5.69 | 39.0 |
| Pryanishnikov's mixture containing 4 N norms | 50.0 | 105±5.41 | 32.0 | 45.0 | 96±4.27 | 15.0 |
| The same + potassium humate 10 mg per 1 l | 68.0 | 135±6.64 | 65.0 | 65.0 | 128±7.60 | 32.0 |
| Pryanishnikov's mixture containing 8 N norms | 37.5 | 98±4.18 | 12.0 | 12.0 | 94 ±4.10 | 4.0 |
| The same + potassium humate 10 mg per 1 l | 37.5 | 96±6.36 | 38.0 | 38.0 | 99±9.12 | 12.0 |
These data show that:
- Plants whose roots were in an environment with reduced oxygen content suffered more from high nitrogen doses than those that were well aerated.
- The effect of potassium humates against the background of 4 nitrogen doses was more noticeable than with a single dose.
- The effect of humates was relatively higher with a lack of oxygen in the medium.
Consequently, physiologically active forms of a humic nature increase the resistance of plants even when 2 unfavorable factors are superimposed — lack of oxygen and excess nitrogen. However, such an effect from humates is no longer observed in the 8N variant.
We studied the issue of the effectiveness of physiologically active humates in the presence of $K$ bicarbonate and concluded that under the influence of humic acids, the resistance of plants (tomato test culture) to the toxic effect of $KHC0_3$ increases.
- This effect is more pronounced again with a reduced amount of oxygen in the root nutrition medium.
- They associate the toxic effects of soda with the precipitation of Fe, which is counteracted by humic acid.
The influence of temperature on the effectiveness of physiologically active forms can be demonstrated by the data in Table 6. It was noticed that in cases where the temperature of physiologically active forms is below the level needed for enzymatic processes, physiologically active forms do not give the proper effect.
| Culture | Experiment Scheme | 14 —18°C | 8 —12°C | ||||
|---|---|---|---|---|---|---|---|
| length of the first order root, mm | number of second order roots, mm | stem length, mm | length of the first order root, mm | number of second order roots, mm | stem length, mm | ||
| Winter wheat | Water | 36 | none | 85 | 36 | none | 75 |
| Potassium humate | 150 | 220 | 200 | 124 | 119 | 95 | |
| Spring barley | Water | 56 | none | 180 | 32 | none | 100 |
| Potassium humate | 173 | 145 | 180 | 280 | 180 | 180 | |
Using $P^{32}$, it was noted that at temperatures that inhibit enzymatic processes, humic substances not only do not stimulate the uptake of phosphorus into the plant but, on the contrary, contribute to its release into the medium.
| Experiment variants | Number of impulses/min per 10 kg of dry matter | |||||||
|---|---|---|---|---|---|---|---|---|
| Experiment numbers 1, 2, 3, 4 | Experiment numbers 1, 2, 3, 4 | |||||||
| t +11 | t +8 | t +22 | t +18 | t +11 | t +8 | t +22 | t +18 | |
| Water + P32 | 1330 | 837 | 323 | 484 | 2156 | 1995 | 683 | 618 |
| Humic acid + P32 | 1226 | 615 | 276 | 334 | 2632 | - | 855 | 767 |
An increase in the relative effectiveness of humic acid can also be observed with a decrease in soil moisture. The experiment was conducted on chestnut soil with spring wheat (Table 8).
- When watering up to 60% of full moisture capacity, humic acid slightly increased the grain yield and slightly reduced the straw yield.
- With insufficient moisture in a later period (watering up to 35% of full moisture capacity), the picture changed sharply. Humic acid had a significant positive effect on the formation of reproductive organs and even contributed to stem growth.
| Experiment Scheme | Fertilized with humic acid | Watering up to 60% of full moisture capacity (g per vessel) | Watering up to 35% of full moisture capacity (g per vessel) | ||||
|---|---|---|---|---|---|---|---|
| stem weight | spike weight | grain weight | stem weight | spike weight | grain weight | ||
| Without fertilizer | No | 11.0 | 7.5 | 5.1 | 6.3 | 4.7 | 3.3 |
| » | Upon filling | 10.8 | 7.9 | 5.4 | 7.0 | 5.4 | 3.3 |
| » | The same + 2 waterings | - 9.3 | 8.0 | 5.6 | 7.4 | 5.8 | 3.7 |
| NP | No | 22.0 | 17.9 | 12.8 | 12.0 | 7.2 | 4.6 |
| Upon filling | 19.2 | 18.1 | 13.0 | 15.3 | 14.0 | 5.8 | |
| » | The same + 2 waterings | - 22.4 | 20.0 | 13.8 | 11.5 | 11.1 | 4.4 |
| **The same, in % of controls** | |||||||
| Without fertilizer | Upon filling | 92 | 105 | 106 | 111 | 116 | 100 |
| » | The same + 2 waterings | 84 | 106 | 109 | 119 | 125 | 112 |
| NP | Upon filling | 87 | 101 | 101 | 120 | 194 | 125 |
| » | The same + 2 waterings | 102 | 111 | 108 | 96 | 154 | 96 |
Note: all vessels were watered up to 60% of full moisture capacity until tillering.
Conclusion: The effectiveness of humic acid is higher when the plant is placed in conditions that deviate from the norm. Humic acid increases the drought resistance of plants.
REGARDING THE NATURE OF THE PHENOMENON AND ITS POSSIBLE SIGNIFICANCE
First of all, it must be noted that a number of medicinal products have long been known in medicine that have the feature of increasing the body's general resistance. These are:
- preparations of ginseng, Siberian ginseng, rhodiola rosea, and other plants;
- synthetic preparations — benzimidazole derivatives, for example, diabazol;
- tissue preparations and stimulants proposed by Academician Filatov.
Most researchers working with these substances believe that the similarity in their action is explained by their direct influence on cells and protein synthesis. As for the nature of the action of physiologically active humic substances on plants, although there is a vast literature on this issue, there is still no theory that can explain the nature of the increase in the general resistance of the plant organism under their influence.
It must be emphasized that in plants, their growth, which is an integral function of many biochemical and physiological processes unfolding in the cells, can serve as a characteristic test of the reaction to external conditions. The determining processes among these should be considered:
- energy processes;
- synthesis of nucleic acids responsible for the transfer of genetic information and information in protein synthesis;
- the synthesis of protein enzymes themselves, which direct and control the entire cycle of cellular metabolism.
Consequently, it can be assumed that the action of physiologically active humic acids, which increase non-specific resistance, should be aimed at normalizing and stimulating those same leading processes of cellular metabolism that are inhibited or blocked by inhibitory environmental factors.
Research carried out by our employees shows that physiologically active humates somewhat alleviate the action of a number of differentiated inhibitors:
- respiration (p-nitrophenol);
- oxidative phosphorylation (2,4-dinitrophenol);
- synthesis of nucleic acids and protein (8-azaguanine, DIC-nuclease, pyrophosphate 1 Ma actinomycin D, chloramphenicol).
At the same time, the blocks of such functionally dependent processes and parameters as mitosis, nuclear volume, and the growth of individual plant organs are removed. To illustrate, here are the results of some experiments (Tables 10, 11).
| Experiment Scheme, seed growing medium | medium onto which seedlings were transplanted | Root length, mm | ||
|---|---|---|---|---|
| 48 hours after transplantation | 72 hours | 96 hours | ||
| Water | Water | 18.8 | 39.6 | 53.4 |
| Potassium humate, 0.005% | Potassium humate, 0.005% | 24.8 | 55.0 | 77.8 |
| 8-azaguanine, $10^{-3}M$ | 8-azaguanine, $10^{-3}M$ | 11.9 | 19.8 | 20.8 |
| 8-azaguanine, $10^{-3}M$ | Water | 11.9 | 34.2 | 44.6 |
| 8-azaguanine, $10^{-3}M$ | Potassium humate, 0.005% | 11.9 | 43.2 | 54.0 |
| Experiment Scheme, seed germination medium | medium onto which seedlings were transplanted | Root length, mm after transplantation | ||
|---|---|---|---|---|
| after soaking, 48 hours | 72 hours | 96 hours | ||
| Water | Water | 18.0 | 39.6 | 53.4 |
| Potassium humate, 0.005% | Potassium humate, 0.005% | 24.8 | 55.0 | 77.8 |
| Potassium pyrophosphate, $10^{-3}M$ | Water | 14.5 | 34.2 | 44.6 |
| Potassium pyrophosphate, $10^{-3}M$ | Potassium pyrophosphate, $10^{-3}M$ | 14.5 | 35.6 | 42.4 |
| Potassium pyrophosphate, $10^{-3}M$ | Sodium humate, 0.005% | 14.5 | 56.2 | 69.2 |
| Experiment Scheme, medium in which seeds were soaked for 48 hours | medium into which seedlings were transplanted for 6 days | Seedling length, mm | Wet weight of seedlings from the dish, g | Protein content in % 'a abs. dry weight | Free amino acid content, mg/% |
|---|---|---|---|---|---|
| Water | Water | 143 | 3.25 | 14.86 | 181.1 |
| Chloramphenicol | Chloramphenicol | 73 | 1.33 | 10.94 | 1230.0 * |
| Chloramphenicol | Water | 98 | 2.10 | 13.57 | 707.2 |
| Chloramphenicol | Potassium humate | 119 | 2.60 | 15.56 | 551.4 |
| Medium in which germinated seeds were held for 24 hours | Seedling growing medium | Number of cells examined, pcs. | Mitotic Index - absolute spread |
|---|---|---|---|
| Water | Water (control) | 5400 | 45.4±4.9 |
| Chloramphenicol, 0.025% | Chloramphenicol, 0.025% | 6000 | 12.5±2.5 |
| » | Water | 6000 | 18.0±3.6 |
| » | Potassium humate $3.1 \times 10^{-5}$ m/l | 6000 | 34.0±3.4 |
It is obvious that under the influence of the studied physiologically active forms, the blocks of leading biochemical and physiological processes at the cellular level are not only removed but also stimulated by them. Special experiments using isotopic methods were conducted to establish the fact of accelerating the synthesis of nucleic acids under the influence of physiologically active humates (Table 14).
| Seeds were germinated on: | Specific activity in impulses per -/ total phosphorus, Kx | T, hours (M±m) | ||
|---|---|---|---|---|
| (M±m) | ||||
| Free nucleotides | Water | 3194±146 | 424±24 | 16.0± 1.0 |
| K humate solution | 4295±172 | 625±35 | 11.0± 1.0 | |
| DNA | Water | 1647± 41 | 196± 5 | 35.0± 1.0 |
| K humate solution | 1985±268 | 243±37 | 29.0± 4.0 | |
| Low-polymer RNA | Water | 1861±187 | 225±25 | 31.0± 3.0 |
| K humate solution | 2633± 94 | 336±14 | 21.0± 1.0 | |
| High-polymer RNA | Water | 541 ± 52 | 61± 6 | 116.0±11.0 |
| K humate solution | 831 ± 78 | 94± 9 | 74.0± 7.0 | |
It is obvious that under the influence of humates, the coefficient of molecule renewal increases. In other words, the assertion that physiologically active humates accelerate the rate of nucleic acid synthesis is confirmed.
Thus, all this experimental material is consistent with the idea that under the influence of physiologically active forms, the plant organism acquires an increased ability for reparative processes at the cellular level, which explains the increase in the plant's overall non-specific resistance.
Ecological Factors and Practical Significance
Nevertheless, there is already reason to believe that the use of physiologically active humic substances to increase the general resistance of plants is possible. A number of conditions, and above all ecological ones, should be taken into account.
Comparing the technology adopted in Poland (processing raw materials with $H_3PO_4 + KHCО_3$) with the technology used in Japan (processing with $HNO_3 + MgCО_3$), he concludes, based on the results of field experiments, that:
- At high ambient temperatures, Polish preparations have an advantage.
- At low temperatures, Japanese ones do.
Touching upon the nature of the biological activity of the preparations, we note that physiologically active humates mainly affect the processes of respiration and photosynthesis in plants.
- Fulvic acids extracted with cold water have the most active influence on oxidative processes during respiration.
- Humato-melanic acids influence photosynthesis.
Application depending on conditions:
- **Fulvic acids:** Provide a positive simulation effect at ambient temperatures above $20°C$, but a negative one at lower temperatures.
- **Humato-melanic acids:** Stimulate the photosynthesis process and partially replace K salts. They yield the best results in variants with a full dose of mineral fertilizers, with a half dose of K salts, and with a small dose of $MgSO_4$.
Prospects in different regions:
- **In humid regions:** Application to the soil in combination with mineral fertilizers and in the form of complex fertilizers is promising. The main active factor is associated with humato-melanic acids.
- **In dry regions:** The use of water-soluble humic preparations in foliar feeding is the most promising. The main active factor is associated with fulvic acids.
It should be emphasized that the ecological approach largely allows for predicting the most promising areas for the application of these substances and determines the optimal options for their use in specific conditions.
When assessing soil fertility, the presence of physiologically active substances in them must be taken into account.
The use of physiologically active substances of a humic nature to combat toxicosis from high doses of mineral fertilizers seems very tempting, especially since they increase the utilization efficiency of mineral nutrition elements.
Practical methods for applying these substances can be various:
- Use of special preparations for root and foliar feeding against a background of mineral fertilizers.
- Complex humic fertilizers obtained on the basis of peat or leonardite.
- Composts and humus.
In light of all the above, it can be said that the further technical progress goes on Earth, the more important the role of both the organic matter of the soil itself and the fertilizers containing them becomes, and the more attention the study of soil and fertilizer humus deserves from the scientific community.