Laws of agriculture

Law of equal significance and irreplaceability of factors of plant life

All factors of plant life are equally significant and irreplaceable.

For the growth and development of a plant, all factors of life must be provided, both cosmic and terrestrial, regardless of the amount of the factor. The absence of one factor, even the smallest, leads to a sharp decrease in yield and death of the plant.

No factor is replaced by another. For example, potassium deficiency cannot be replaced by excess phosphorus, and lack of light cannot be compensated by heat, etc.

Obtaining the maximum possible yields is possible only with a constant supply of all factors of life in sufficient quantity. However, in practice the law of equal significance and irreplaceability of factors is relative due to different costs for providing plants with life factors. This is connected with the possibility of creating in a specific locality such conditions in material-technical, soil, and natural-climatic terms.

The law of equal significance and irreplaceability of factors of plant life lays the material foundation of agriculture: to obtain consistently high yields, one must strive to fully provide plants with all factors.

Law of the minimum

The growth and development of a plant are determined by the factor that is at a minimum.

Justus von Liebig.

It is also called the law of the limiting factor or Liebig's law. The law of the minimum was first formulated by Carl Sprengel in 1828. It was later developed and popularized by Justus von Liebig in the book “Chemistry in Its Application to Agriculture and Physiology” in 1840 using mineral substances as an example. According to his observations, yield growth directly depends on increasing the amount of the factor that is at a minimum, or:

where

Y

— yield;

A

— coefficient of proportionality for a specific factor;

X

— factor intensity.

The discovery of the law of the minimum made it possible in the second half of the 19th century to significantly increase the yields of crops traditionally cultivated in Central Europe by applying mineral fertilizers on depleted soils.

Liebig's barrel.

Graphical representation of the law of the minimum: 1 — maximum possible yield; 2 — actual yield

Traditionally, to illustrate the law of the minimum, the “Dobenek barrel” or “Liebig's barrel” is used. The staves (boards forming the side surface) represent various factors of plant life. The height of the staves equals the amount of a certain factor. The less a plant is provided with a specific factor, the lower the height of the stave. It is precisely this that determines the actual yield, despite the fact that other factors may be maximal, ensuring the potential yield of the crop. If the height of the shortest board is increased by adding the corresponding factor, then the actual yield will already be determined by another stave that turns out to be at a minimum.

Despite the obviousness and simplicity of the law, subsequent studies established a number of clarifications. J. von Liebig recognized a diminishing effect with each increase of an individual factor. A. Mayer proved: the law of the minimum should be taken into account with the entire set of factors, and not only nutrients. E. Wollny expanded the operation of the law in the aggregate of factors to the quality of the yield.

Law of minimum, optimum, and maximum

Maximum development of a plant is possible with optimal provision of life factors.

In the course of a number of experiments, this law was subjected to checks and refinements, as a result of which it was not confirmed.

The law of minimum, optimum, and maximum was proposed as a result of a number of studies; the best-known is Hellriegel's experiment. He grew barley in glass vessels filled with the same fertile soil. All conditions of plant growth were the same, except for soil moisture, determined by full water-holding capacity of 100%. In 8 vessels, moisture was 5, 10, 20, 30, 40, 60, 80, and 100%. At the end of the experiment, yield was distributed as follows:

The maximum barley yield in Hellriegel's experiments occurred at soil moisture of 60% FWHC. Minimum and maximum amounts of moisture did not ensure yield. If we express the difference in yield increment for each next moisture gradation, referred to a unit of moisture, then we obtain a progressively decreasing increase in yield from successive moisture increments while the other factors remain unchanged. This pattern was called Thünen's law.

V. R. Williams analyzed Hellriegel's experiment and showed the particular nature of the obtained pattern. He established that Hellriegel's experiment violates the condition of the single logical difference, which is the most important requirement of an agronomic experiment. Different soil moisture does not create identical conditions for plant nutrition. Moisture is inseparably connected with redox conditions in the soil, and consequently substantially affects soil biochemical processes.

Thus, Hellriegel's experiment is essentially unreliable, and its conclusions are erroneous. This is confirmed by data from E. Wollny's experiment. Under the same conditions as in Hellriegel's experiment, except for fertilizer that cannot be reduced under anaerobic conditions, the results obtained are given in the table.

E. Wollny's experiments showed a completely different character of the dependence of yield on soil moisture compared with Hellriegel's curve: an increase in moisture causes a progressive increase in yield increment per unit of moisture, rather than a decrease.

According to V. R. Williams, E. Wollny's experiment also had methodological shortcomings. Subsequently, E. Wollny conducted a multifactorial experiment on spring rye plants, growing them in three rows of glass vessels, four vessels in each row.

In each row there were three vessels with moisture of 20, 40, and 60% FWHC with unfertilized soil; in the fourth vessel of each row, fertilized soil with moisture of 60%. The illumination of each row was different (weak, medium, strong). The results are presented in the table and figure.

E. Wollny's experiment.

Dependence of yield on growth factors: lighting, moisture, fertilizer.

The increase in yield in vessels with unfertilized soil as moisture increased repeats the results of Hellriegel's experiment. The introduction of fertilizer led to a sharp increase in yield in vessels with soil moisture of 60%. However, adding the lighting factor to the experiment sharply increased the effectiveness of fertilizer. If we sum the yields of the fertilized variants under different lighting, it turns out that the interaction of all factors gives a significant increase in yield, increasing as new factors of plant life are added to the system. These conclusions also refute Thünen's law.

Law of the combined action of factors of plant life

All factors of plant life interact in the process of plant growth and development, that is, they act in combination.

Liebscher and Lundegårdh showed that the more other factors of plant life are at optimum, the more intense is the action of the factor at minimum. Lundegårdh also established the aggregate negative effect on plant development of factors at minimum, calling it “interference” of factors.

Based on the law of the combined action of factors of plant life, a number of researchers attempted to establish a mathematical dependence of yield on life factors. The greatest success was achieved by E. Mitscherlich, who tried to find a mathematical dependence of yield increase on soil fertilization. He established that the yield increase is proportional to the difference between the maximum possible and actually obtained yield and depends on each factor and its intensity. E. Mitscherlich experimentally determined coefficients of utilization of individual nutrients: for nitrogen N — 0.2, phosphorus P₂O₅ — 0.6, potassium K₂O — 0.4, magnesium Mg — 2.0 per 1 mm of precipitation. Subsequent studies showed that E. Mitscherlich's dependence is not universal due to the complexity of biological processes of yield formation. Moreover, soon Trenel showed that it is mathematically incorrect.

Despite the difficulties of mathematical expression of this law, it is important in agricultural practice. V. R. Williams pointed out that maximum yield return can be achieved only with simultaneous action on the entire complex of factors of plant life, which represents a single organic whole whose elements are inseparably linked. Action on one of the factors of life entails the need to act on all the others.

Law of return

Substance and energy removed from the soil with the harvest must be compensated (returned to the soil) with a certain degree of excess.

First discovered by J. von Liebig. D. N. Pryanishnikov and K. A. Timiryazev considered the law of return one of the greatest for science.

Agriculture by its nature as a branch of production is material: the harvest is created from material components — energy and substances consumed by plants from the soil. Soil is also the medium of plant growth and an intermediary in providing them with life factors. Systematic removal of the harvest from fields without returning the energy and soil components used by it leads to loss of soil fertility. If the removal of energy and substances is compensated, soil fertility is preserved; and with compensation in excess, reproduction of fertility occurs.

The law of return is the scientific basis for reproduction of soil fertility. It can be considered a special case of the physical law of conservation of matter and energy.

Law of crop rotation

Alternation in time and space of cultivated plants differing in biochemical, biological, agronomic, and other properties.

The law of crop rotation is the scientific basis of the “principle of crop rotation” or proper crop rotation. Its basis is the law of unity and mutual influence of plants and environmental conditions.

Professor M. G. Pavlov as early as 1838 recognized the law of crop rotation as a law of nature: Any agrotechnical measure is more effective under crop rotation than under permanent sowing.

Other laws of agriculture

In agriculture there are a number of other laws: the law of autotrophy of green plants, based on the theory of photosynthesis and mineral plant nutrition; the law of intake, movement, and transformation of mineral substances in plants, etc.

Erroneous interpretation of the results of some studies in which only one factor was changed while the others remained constant led to the formulation of the “law of diminishing soil fertility” or the Turgot-Malthus law, or the law of diminishing returns. It consists in the fact that each additional investment of funds and labor in land is accompanied not by a corresponding but by a decreasing increase in yield.

V. I. Lenin criticized these conclusions:

… the "law of diminishing soil fertility" is not at all applicable to those cases when technology progresses, when methods of production are transformed; it has only a very relative and conditional application to those cases when technology remains unchanged.

Lenin V. I. Complete Collected Works. Vol. 5. p. 102.

Subsequently, experimentally, with simultaneous action on all factors of plant life, the complete unsoundness of the “law of diminishing soil fertility” was established. Thus, in experiments with three simultaneously changing factors — light, nutrients, and soil moisture — it was shown that with full satisfaction of plants with these factors, yield continuously increased.

This increase in yield is limited only by the biological nature of the plant, as well as by the level of development of science and technology. F. Engels came to a conclusion directly opposite to the “law of diminishing soil fertility”:

“The productive force at humanity's disposal is limitless. The yield of the land can be infinitely increased by the application of capital, labor, and science.”

The experiments of V. R. Williams, E. Wollny, and other scientists showed similar results: optimal supply of plants with light, moisture, and nutrients makes it possible to increase yield several times with significantly lower consumption of nutrients and moisture per unit of production. These conclusions made it possible to successfully introduce and use intensive technologies of cultivating agricultural plants, based on all the laws of agriculture, taking into account local soil and climatic conditions and the characteristics of the species, variety, and cultivar of the crop.

Practice of applying the laws of agriculture

The developed farming systems are based on the operation of the laws of agriculture. Modern directions of adaptive-landscape farming systems are built on the use of land resources of a certain agroecological group, oriented toward economically profitable production of high-quality products in accordance with market needs, ensuring the sustainability of the agrolandscape and constant reproduction of soil fertility. The development of farming systems is inseparably linked with the development of new technologies, one of the main requirements for which is adaptability to natural conditions, forms of management, various levels of production intensification, etc.

The methodology for constructing technologies is based on the laws of agriculture. For example, guided by the law of the minimum, limiting factors of yield are identified and eliminated taking into account soil and climatic conditions, specialization, and level of production intensification. Intensification of production changes the significance of certain factors: with the elimination of the deficit of some, the role of others increases. The return of nutrients removed with the harvest, according to the law of return, must be compensated in excess for constant expanded reproduction of fertility.

Non-observance or violation of the laws of agriculture in agricultural practice leads not only to failure to obtain expected results but also to negative results with unjustified economic costs. For example, unjustified land reclamation, intensive technologies, chemicalization, reforming the AIC. Without taking into account the complex of mutual and systemic connections, factors and practices that seemed justified, necessary, and environmentally sound ultimately led to negative consequences for the functioning of agricultural production.

High yields are ensured by combinations of certain factors of plant life at each stage of development. Only with the combined action of all life conditions is full use of each of them possible, which is rarely encountered in practice. More often, the factor at a minimum determines yield formation under specific soil and climatic conditions. For example, in the Non-Chernozem zone these are nutrients; in arid regions, water. Each agrotechnical practice, as a rule, affects 1–2 factors of life in order to create favorable conditions for plant growth and development. Therefore, only a complex of measures makes it possible to regulate all conditions of plant life. Obviously, the greatest significance among these agropractices will be that which affects the factor at a minimum.

In addition to the soil and climatic characteristics of the zone or locality, when developing a complex of agrotechnical measures, the phases of plant development should be taken into account. Practices should ensure an increase in reserves of organic and mineral substances in the soil, increasing its fertility and improving its structure and composition.

List of sources

1. Niklyaev V. S. Fundamentals of Agricultural Production Technology. Agriculture and Crop Production. Moscow: “Bylina”. 2000.
2. Bazdyrev G. I., Loshakov V. G., Puponin A. I. et al. Agriculture. Textbook for Universities. Moscow: “Kolos” Publishing House. 2000.