Laws of agriculture and principles of crop productivity formation

Subsequently, R. Sachs expanded and transformed this law into the law of the minimum, maximum, and optimum, according to which the highest harvest is achievable given an average (optimal) presence of a specific factor. At the minimum and maximum values of this factor, the harvest becomes impossible altogether.

The law of the combined action of plant life factors. Individual factors of life do not act in isolation, but in close interaction with each other. Plants are continuously influenced by the entire complex of factors. They manifest their strength to the greatest extent only through combined action. Later, E. Mitscherlich gave this law a mathematical expression in the form of

C (AY) where Y is the expected harvest; X is the intensity of the factor under study; C is the coefficient of the variable factor's action; A is a conventional constant characterizing the highest harvest.

The main corollary of the law of the combined action of factors is the principle that the highest efficiency of land use cannot be ensured by any single agrotechnical practice; a complex of necessary measures must be implemented.

Another corollary of the law of the combined action of factors is the law of adequate interdependence between the phytocenosis and the biotope (simplified: the unity of organisms and the environment). This law has been established and confirmed by numerous studies by geobotanists and ecologists.

The essence of the law of adequate interdependence between the phytocenosis and the biotope is as follows. Under natural conditions, a specific plant community (phytocenosis) forms in each concrete territory. In the process of long-term selection, as a consequence of many years of interspecific and intraspecific competition and various forms of relationships between plants, a community stable in its floristic (species) composition, structure, and productivity is formed. Different species complement each other in utilizing both terrestrial and underground space, as well as the time interval, due to the natural succession of some species by others throughout the growing season. The organic mass formed in the community, as well as the various mineral elements contained within it, remains almost entirely at the place of growth (ecotope). Under the influence of vegetating plants, their root systems, vital secretions, processes of decomposition and mineralization of plant residues, and the vital activity of soil-dwelling organisms (microbes, fungi, nematodes, larvae of insects, earthworms, etc.), the place of growth—and not just its part, the soil—is transformed into a habitat (biotope). Under these life conditions, the biotope optimally corresponds to the requirements of the specific plant community: its productive capabilities reach a natural maximum.

With the intensification of the aforementioned processes, the natural plant community acquires such important properties as resistance to natural disturbances and stability in the formation of organic matter. And the more species there are and the more diverse the forms of relationships between them, the more stably the community functions. Later, it acquires a new unique property: the ability for self-regulation, or, in other words, the ability for full-scale self-reproduction, including in terms of composition and structure. The community moves into a qualitatively new state called a biocenosis or ecosystem.

When involved in agricultural production, the entire natural plant community with its established structure, composition, and relationships is completely destroyed. In ploughed territories, crop plants are cultivated to solve the most important task of agriculture: to obtain the largest amount of crop production of a certain quality from each hectare of sowing. Therefore, in comparison with natural communities, agricultural crops have a number of features: they are usually monospecific, more often represented by annual plants, the removal of mineral nutrients with the harvest exceeds their input into the soil with the insignificant amount of plant residues, soil fertility steadily declines, the infestation of crops with harmful organisms increases due to the cultivation of one crop for two or more years in a row in the same field, the yield of plants drops and fluctuates strongly by year, etc.

To avoid these and similar negative phenomena in farming, various methods of crop cultivation have been constantly tested. First of all, due to the relative simplicity of the technical solution, the aim was to sow crops that are completely different in their biology in the same field year after year.

V. D. Pannikov based the most important principle of farming—crop rotation—on what is stated above. Its essence lies in the alternation of crops in space and time, which allows, all other things being equal, to obtain a higher harvest than with repeated sowings of the same crop in the same field (monoculture). The necessity of a periodic change of different crops in fields is determined by the fact that each of them affects the soil and the environment differently, changing the agrophysical, hydro-air, thermal, and nutrient regimes of the soil along its vertical profile, as well as the composition of microflora and the intensity of the development of pathogenic organisms. On the basis of this law, scientific principles of crop rotation are developed. For example, by year, sowings or even sowings and fallow fields are alternated in one field: perennial grasses — winter wheat — potato — 3.1. Concept of a crop cultivar and features of its creation 51 oats — green fallow — winter rye, etc. Compliance with this principle in farming practice allows for the elimination of many, but far from all, negative phenomena of modern agriculture. Therefore, the principle of crop rotation objectively expresses only part of the law of adequate interdependence between a natural plant community and the conditions of its habitat.

The law of return of nutrients. K. Marx called its discovery one of the greatest merits of J. Liebig. According to this law, if the balance of available nutrients in the soil is disturbed due to their removal with the harvest or as a result of other reasons, it must be restored by applying appropriate fertilizers to the soil. This is of great importance for maintaining soil fertility, achieving high yields, and obtaining produce of the required quality.

Transformation of the laws of agriculture in the 20th century

In the 20th century, the law of return of nutrients was transformed into the law of increasing soil fertility, or the progressive growth of effective soil fertility as agriculture intensifies.

The operation of this law manifests itself when other laws of agriculture are observed, especially the law of return of nutrients, since a significant part of these substances is annually removed with the harvest, which gave R. Malthus a reason to speak of diminishing soil fertility.

However, with a rational, non-predatory approach to the soil as a result of agricultural intensification, driven by:

• mechanization and chemicalization of technological processes;
• fertilizer application;
• reduction in the number and harmful effects of weeds, diseases, and pests;

on the contrary, the productivity of field soils increases.