The laws of return of nutrients and tolerance in soil fertility

The Law of Return of substances to the soil: "All substances used by plants in the creation of a harvest must be fully returned to the soil with fertilizers."

This law, discovered by J. von Liebig (1840), is the scientific basis for the reproduction of soil fertility, a special case of the manifestation of the universal law of conservation of matter and energy; violation of this law, according to the author, "sooner or later must lead to the loss of soil fertility." K.A. Timiryazev (1896) called this law "the greatest discovery of science."

Application of fertilizers is an important means of maintaining and reproducing soil fertility and increasing the productivity of cultivated plants. Nutrients entering the soil with fertilizers help plants more effectively utilize soil moisture, solar energy, and other ecological factors, thereby more fully realizing their potential. The results of studies on the cycle and balance of nutrients in agriculture provide a clear picture of the agrochemical state of soils and the necessary quantities and composition of fertilizers. This allows for maintaining a non-deficit balance of nutrients in the soil.

Commenting on the "law of return," A.M. Lykov, A.A. Korotkov, G.I. Bazdyrev, et al. (1990) note that agriculture as an industry is material in its nature. The harvest, as a material substance, is created from material components, a certain part of it being derived from substances and energy obtained by plants from the soil. Furthermore, the soil is a unique intermediary for plants in providing the factors of life, their growth medium. When the removal of substances and energy from the soil is compensated for, the latter retains its fertility; when substances and energy are compensated for with a certain degree of excess, soil improvement and "expanded reproduction" of its fertility occur.

Law of Tolerance

Law of Tolerance: "The limiting effect on the harvest is exerted not only by a deficiency but also by an excess of any factor." In essence, this law expands and supplements the "law of minimum." The law of tolerance was first formulated by V. Shelford (1913, 1934). The very concept of "tolerance" signifies the endurance of an organism in relation to fluctuations of any ecological factor. Here, the range between the ecological minimum and maximum of a factor constitutes the so-called "limit of tolerance" – the measure of an organism's endurance to a given factor.

The biological and agronomic meaning of the law of tolerance lies in the fact that both an ecological minimum and maximum are characteristic of the growth and development of plants. This law was supplemented by E.P. Odum (1975) with the following fundamental points:

– the range of tolerance of organisms to various factors is not identical. Thus, plants develop normally within a wider range of phosphorus concentrations in the soil than that of nitrogen;

– if conditions for one ecological factor are not optimal for a given plant species, the range of tolerance to other factors may narrow. Thus, with a change in air temperature, the range of tolerance to humidity changes;

– often, conditions found to be optimal in short-term laboratory or pot experiments for a given plant turn out to be sub-optimal under field conditions. In this case, the discrepancy in the optimality of factors is linked to the fact that a vegetation pot as a physical model is not similar to a field based on a number of criteria;

– the limits of tolerance to any factor are not constant throughout ontogenesis. There are critical periods during which many factors are limiting. Thus, alfalfa seedlings die at a pH level at which mature plants are capable of developing.

Law of Crop Rotation

Law of Crop Rotation: "Any agrotechnical measure is more effective under crop rotation than under continuous sowing."

A major role in the substantiation and scientific formulation of this law in the late 18th and early 19th centuries was played by A.D. Thaer. He proposed restructuring the agricultural system based on maintaining the amount of humus in the soil at a constant level. The scientist saw the solution to this problem in "crop rotation" – the alternation of agricultural crops with different root systems. "The introduction of crop rotation is indeed a great merit of Thaer," notes one of the leading national soil scientists L.O. Karpachevsky (1983).

In the interpretation of V.V. Ermolenkov, A.A. Shalyuto, V.N. Prokopovich, et al. (1998), the essence of this law lies in the fact that "higher yields are obtained with crop rotation in space and time than with continuous sowing." The necessity of alternating different crops in fields is due to the fact that various crops influence soil properties and the surrounding environment in different ways.

Substantiating the reasons and significance of alternating agricultural crops in a crop rotation, from the perspective of increasing their yield, D.N. Pryanishnikov wrote as early as the beginning of the 20th century: "The reasons why correct crop rotation of cultivated plants proves more productive than the continuous cultivation of the same crop (or plants more or less identical in their properties) can be divided into 4 groups:

1) chemical causes, i.e., differences in the chemical composition of plants and their consumption of nutrients;

2) physical causes, i.e., differences in soil condition and soil moisture after harvesting different crops;

3) biological causes, i.e., different responses of crops to diseases, pests, and weeds;

4) economic causes, i.e., differences in the quantity and timing of labor required by crops, and their different significance for the farm."

According to V.D. Pannikov and V.G. Mineev (1977), one should also keep in mind the reasons associated with the varying soil-protective roles of certain agricultural plants, as well as the ameliorative significance of some crops, primarily perennial grasses in crop rotation under irrigated farming. They also draw attention to the great importance of proper crop rotation for the rational use of the soil water regime.

The basis of this law lies in the general biological law of unity and interrelation between plant organisms and environmental conditions. The necessity of rotating different crops in fields is determined by the fact that various crops influence soil properties and the environment in different ways. Agrophysical properties of the soil, as well as water, air, heat, and nutrient regimes, change differently. Each crop or group of crops has its own biological characteristics regarding its influence on the composition of soil microflora and the intensity of development of specific physiological groups of microorganisms. It is precisely on the basis of this law that the principles of developing modern crop rotations are formulated.

The Law of Correspondence of a Plant Community to its Habitat

"The Law of Correspondence of a Plant Community to its Habitat: "Each (any) plant community must fully correspond to its habitat"."

As noted by Yu.A. Shtompel (1999), in developing the soil and water conservation concept of A.A. Zhuchenko (1990) as one of the laws of agriculture that must be taken into account when creating sustainable agrolandscapes, the correspondence of a plant community to its habitat is essential. Since each crop possesses species-specific ecological stability, correct agroclimatic macro- and micro-zoning of cultivated plants is necessary." This law, in the scientist's opinion, is of great importance for anti-erosion agriculture practiced on sloping lands.

The Law of Autotrophy of Green Plants

The Law of Autotrophy of Green Plants: "Green plants, using solar energy and absorbing carbon dioxide from the air, and water and mineral compounds from the soil, synthesize all the organic substances they need in quantities that ensure the full development and high yield of the plants."

As noted by V.P. Nartsissov (1976), in terms of the time of discovery and general significance in biology and agronomy, this law should be given first place – it united the theories of photosynthesis and mineral nutrition of plants. In accordance with this law, one of the fundamental principles in yield formation should be the rapid development of an optimal leaf surface capable of maximizing the absorption of solar energy for the synthesis of sugars, amino acids, proteins, enzymes, and other compounds from which new cells, protoplasm, tissues, and plant organs are created.

The Law of Ion Antagonism

The Law of Ion Antagonism: "Certain chemical elements, when present in excess in the soil or in a solution, hinder the absorption of other elements by plants."

This law was first formulated in the mid-19th century by the Scandinavian scientist Oscar Löw. The conclusion that follows from this law: the ratio of elements in the soil must be optimal – otherwise, certain chemical elements present in excess may hinder the absorption of other elements by plants. Therefore, if the ratio of elements in the soil is incorrect, their uptake by the plant can be significantly impeded.