Phytosanitary condition of the soil is a soil characteristic, reflecting the content of seeds and vegetative organs of reproduction of weeds, phytopathogens, pests, toxic substances produced by plants and soil microflora, as well as by decomposition products. All these factors are part of agrobiocenosis.
The majority of pests in the soil, in spite of differences in their biological properties, can be characterized by common features: high fertility, relatively narrow specialization of affected plants, high adaptation to changing external conditions, which provides them with high competitive qualities.
Phytosanitary state has a significant impact on crop yields. To assess the phytosanitary state of soil and crops, the thresholds of harmfulness of weeds and harmful effects of pests and phytophages are taken into account. Achievement of absolute cleanliness of crops in practical terms is difficult to achieve and economically unjustified, so in agriculture it is customary to control the number of pests and plants, keeping their populations at a level that does not cause economically significant damage, that is, when the economic cost of control exceeds the economic benefits of increased production.
The number of pests of plants and organisms is regulated through the development and application of a single set of measures, including a variety of agrotechnical, agrochemical, biological, cultural and other methods.
Phytotoxicity of soil
Soil phytotoxicity, or soil toxicosis, is the accumulation by the soil of physiologically active substances represented by a wide range of organic compounds called colins.
The composition and amounts of colins depend on many factors, such as soil moisture and temperature, a variety of soil microflora and growing plants.
Colins affect all processes of plant life, and, depending on concentrations, their effect can be both stimulating and depressing. For example, according to the data of stationary experiments of the Moscow Agricultural Academy it was established that soil aqueous extract taken at the beginning of spring vegetation from permanent crops of barley and winter wheat reduced seed germination of these crops by more than 20% and suppressed the growth of the root system, which was one of the causes of the thinned permanent crops.
Colins enter the soil from plant root excretions, decomposition of plant residues, and in the form of products of microorganisms. The greatest accumulation of phytotoxic substances is observed when growing plants of the same species or with similar biological properties, as well as on soils with anaerobic conditions.
Cultivation of the same species or plants with similar biological properties on the same site annually receives approximately equal amounts and composition of organic matter in the form of root excretions and residues. As a result, the ratio of microorganisms and phytotoxic compounds in the soil changes. For example, crop residues accumulate phenolic compounds, which have a depressing effect on the development of the crop itself and other crops.
Anaerobic conditions, i.e., airy soil conditions with severe oxygen deficiency, 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, having adverse effects.
Toxins released by some bacteria can affect respiratory and photosynthetic processes, cause changes in chemical composition and disrupt metabolism in plants, particularly nitrogen metabolism, which changes the ratio of protein and non-protein nitrogen, the accumulation of some amino acids, ammonia and other nitrogen compounds.
Various substances excreted into the soil by plants, such as amino acids, carbohydrates, become a source of energy for microorganisms and participate in the metabolism of plant cells of other plants. Thus, excretions of root systems (exudates), stimulate the development of root rot fungi, ophiobolus conidia, and others. On the other hand, some components of root excretions, on the contrary, show inhibitory properties.
Phytotoxins can also have positive effects. For example, colins excreted by soil microflora can have a suppressive effect on pathogenic fungi.
The diversity of phytoactive substances is huge and their cross influence in agrocenoses is even more so. The study of these properties is one of the areas of modern science, which opens up the potential to regulate the phytosanitary state of the soil, through which you can significantly affect the environmental and economic efficiency of agriculture, which in several countries is realized and implemented in agricultural technology.
Reproduction of phytosanitary condition of soil
To reproduce the phytosanitary condition of the soil, the following measures and techniques are used:
- scientifically based alternation of crops, i.e. replacement of one crop with other crops with different properties;
- use of varieties resistant to pests and diseases;
- rational use of tillage technologies;
- use of intermediate crops;
- carrying out sanitary and preventive measures;
- use of chemical and biological means of plant protection.
Farming. Textbook for universities / G.I. Bazdyrev, V.G. Loshakov, A.I. Puponin et al. – Moscow: Publishing House “Kolos”, 2000. – 551 с.