Fundamental laws of plant nutrition and life factors

The law of equivalence and irreplaceability of plant life factors: "All plant life factors are absolutely equivalent and irreplaceable; no single life factor can be replaced by another."

According to this law, the growth and development of plants must be provided with an influx of all plant life factors—both cosmic and terrestrial (light, heat, air, water, elements of mineral nutrition). The absence of any one of them leads to the death of plants, and one factor cannot be replaced by another. For example, the fact that plants consume a large amount of water and relatively few mineral nutrition elements in the process of their vital activity does not in any way signify the superiority of water as a factor. A plant may die even due to a lack of a single microelement—such as boron or copper; at the same time, a boron deficiency cannot be compensated for by copper or zinc, just as nitrogen cannot be replaced by phosphorus or potassium, and vice versa. In the formulation by V.R. Williams (1939), this law states: "For their life, plants require the simultaneous and joint presence or an equal influx of all conditions or factors of their life without exception."

V.V. Yermolenkov, A.A. Shelyuto, V.N. Prokopovich, et al. (1998) note that the manifestation of this law is both absolute and relative in nature. The absolute value is expressed by the fact that a plant may require both large and infinitesimal quantities of factors, yet the absence of any one of them is equivalent to the death of the plant. In practice, obtaining the maximum possible harvest is only possible with an uninterrupted supply of all life factors to the plants in optimal quantities. However, in specific production conditions, this law acquires a relative value due to the unequal costs of providing plants with different factors.

The law of equivalence and irreplaceability of plant life factors emphasizes the materiality of agricultural production and does not allow for reliance on "miraculous" recipes for obtaining a harvest without material costs or costs in "homeopathic doses."

Law of the Minimum

The law of the minimum was first formulated by J. Liebig in 1840: "The productivity of a field is in direct dependence on the necessary constituent part of plant food contained in the soil in the most minimal quantity." He believed that the growth in harvest is directly proportional to the increase in the quantity of the factor that is in the minimum:

where: Y – harvest;

X – intensity of the factor;

A – coefficient of proportionality for the given factor.

The identification of this regularity had immense practical significance, as the application of mineral fertilizers">application of mineral fertilizers first received a scientific basis. According to this law, under optimal conditions for all other factors, the level of harvest is determined by the factor that is in the minimum. J. Liebig illustrated the "law of the minimum" with various examples. For instance, if we have a chain supporting a certain load, and we gradually increase that load, when will the chain break? – When the weakest link snaps. Thus, in order for the chain to be stronger, one must first find and strengthen that very weakest link.

According to D.N. Pryanishnikov (1965), the so-called "Döbeneck's barrel" is best suited to illustrate this law—a wooden barrel where the individual staves (planks) are not of the same height—one is higher, the other is lower.

Such a barrel can be filled with water only up to the height of the lowest stave. Similarly, the harvest can only be raised to the level at which the nutrient is in the minimum. Until you have found this minimum factor, you will not increase the harvest.

Fig. 88. Graphic representation of the law of the minimum:

1 – maximum possible harvest; 2 – actual harvest.

Despite the apparent simplicity and obviousness of this law's operation, it still bears a relative character. This was experimentally confirmed by A. Mayer, E. Wollny, J. Sachs, H. Hellriegel, and V.R. Williams. Thus, A. Mayer showed that the law of the minimum must be taken into account not only regarding the action of plant nutrients but also the entire aggregate of life factors. E. Wollny extended the law of the minimum to harvest quality, establishing the dependence of the effect of an individual factor on the entire set of other factors. In vegetation experiments, H. Hellriegel established the dependence of plant productivity on soil moisture. As follows from his data, the maximum harvest corresponds to an optimal soil moisture of 60% of its full water-holding capacity. In the absence of moisture, as well as in its excessive abundance, the harvest was zero. The change in harvest depending on soil moisture confirmed the decreasing efficiency of successive equal quantities of any plant life factor.

R. Sachs (1857), building on the research of A. Mayer, E. Wollny, and H. Hellriegel, formulated the law of minimum, optimum, and maximum: "The yield magnitude is determined by the factor that is in the minimum. The highest yield is achievable with the optimal presence of a given factor. With the minimum and maximum presence of a factor, a yield is impossible." Later, V.R. Williams (1939) somewhat specified this law: "The highest yield is achievable with an average 'optimal' presence of a factor; with the smallest (minimum) and largest (maximum) presence of a factor, a yield is unachievable (equal to zero)." The reaction of plants to minimum, optimum, and maximum temperatures, lack or excess of soil moisture, and an increase in fertilizer application rates are the result of this law.

Guided by the "law of minimum" in various soil and climatic zones of the Russian Federation, under conditions of different levels of production intensification and degrees of specialization, factors limiting yield growth are identified and eliminated. Thus, the intensive application of mineral fertilizers in a number of regions of our country has led to an increased response of field crops to micronutrient fertilizers. At the same time, as agriculture intensifies, the regulation of the water regime and the acid-base properties of the soil becomes increasingly relevant; ensuring the soil with organic matter becomes particularly relevant in this context. At the same time, the works of E.P. Odum (1975) and A.S. Obraztsov (1990) note that the "law of minimum" is strictly applicable only under steady-state conditions, when the influx of matter and energy is balanced by their outflow. If the balance of any substance is disturbed, the growth rate of biomass changes, the steady state and the "minimum effect" are absent, and the result already depends on all components. This state, according to the scientists, can continue until the "inflow-outflow" equilibrium is restored and the growth rate is again limited by the factor that is in the minimum.