Phytosanitary condition of soil
Phytosanitary condition of soil — a soil characteristic reflecting the content of seeds and vegetative reproductive organs of weeds, phytopathogens, pests, and toxic substances formed as a result of the activity of plants, soil microflora, and decomposition products. All the listed factors are part of agrobiocenosis.
Most harmful organisms present in the soil, despite differences in their biological properties, can be characterized by common features: high fecundity, relatively narrow specialization in the plants they affect, and high adaptation to changing conditions, which gives them strong competitive qualities.
Importance
The phytosanitary condition of soil affects the yield of agricultural crops.
Soil phytotoxicity
Soil phytotoxicity, or soil fatigue, soil toxicosis, — the accumulation in soil of physiologically active organic substances called colins. Soil fatigue is also associated with the accumulation of characteristic pathogens and products of their activity.
Colins
The composition and amounts of colins depend on many factors, such as soil moisture and temperature, the diversity of soil microflora, and the plants growing.
Colins affect all vital processes of plants. Depending on the colin content, their effect can be either stimulating or suppressing. For example, an aqueous soil extract taken at the beginning of spring vegetation from continuous crops of barley and winter wheat reduced the seed germination of these crops by more than 20% and suppressed root system growth, which became one of the causes of sparseness in continuous crops (long-term stationary experiments at MAA).
Colins enter the soil from root exudates of plants, during decomposition of plant residues, and as products of microorganism activity. The greatest accumulation of phytotoxic substances is observed when plants of the same species or with similar biological properties are grown in the same place, as well as on soils with anaerobic conditions. When plants of one species or with similar biological properties are cultivated in the same place, organic matter approximately equal in quantity and composition enters annually in the form of root exudates and residues. As a result, the ratio of microorganisms and phytotoxic compounds in the soil changes. For example, plant residues of cereal crops accumulate phenolic compounds, which have a suppressive effect on the development of the crop itself and other cereals.
Anaerobic conditions, i.e., a soil air regime with a severe oxygen deficit, create favorable conditions for the development of anaerobic soil microflora, which leads to the formation of phytotoxic substances. Some microorganisms are able to concentrate around the root system of plants, thereby locally increasing the adverse effect. Toxins secreted by some bacteria can affect respiration and photosynthetic processes, cause changes in chemical composition, and disrupt metabolism in plants, in particular nitrogen metabolism, as a result of which the ratio of protein and non-protein nitrogen changes, and some amino acids, ammonia, and other nitrogen compounds accumulate.
Various substances released into the soil by plants, such as amino acids and carbohydrates, become a source of energy for microorganisms and participate in the metabolism of plant cells of other plants. Thus, root system exudates stimulate the development of root rot fungi. On the other hand, some components of root exudates, by contrast, exhibit inhibitory properties. For example, colins released by soil microflora can have a suppressive effect on pathogenic fungi.
Assessment of the phytosanitary condition of soil
To assess the phytosanitary condition of soil and crop stands, thresholds of weed harmfulness and the harmful effect of pests and phytophages are taken into account.
Management
Achieving absolute cleanliness of crops is practically difficult to achieve and economically unjustified; therefore, in agriculture it is customary to control the abundance of harmful organisms and plants, keeping their populations at a level that does not cause economically significant damage, that is, when the economic costs of control exceed the economic benefits from the increase in production.
Regulation of the abundance of harmful plants and organisms is carried out by applying an integrated set of measures including agronomic, agrochemical, biological, and cultural methods:
- scientifically based crop rotation;
- use of varieties resistant to pests and diseases;
- rational use of soil tillage technologies;
- use of intermediate crops;
- carrying out sanitary and preventive measures;
- use of chemical and biological plant protection products.
The diversity of phytoactive substances and, moreover, their cross-influence in agrocenoses is enormous. The study of these properties is one of the areas of modern science that opens up the potential for regulating the phytosanitary condition of soil. Regulation of the phytosanitary condition makes it possible to influence the ecological and economic efficiency of agriculture.
References
- Bazdyrev G. I., Loshakov V. G., Puponin A. I., et al. Agriculture. Textbook for universities. Moscow: Kolos Publishing House. 2000.
