Associative microorganisms live in the zone of direct influence of plants namely in the soil, which is in close contact with the roots. They form complex communities on the roots of plants in terms of taxonomic composition and structural and functional o8rganization, which have polyfunctional effect on plants. Rhizosphere biotechnologies with the use of associative bacteria to a specific plant species allow increasing their productivity and quality, which contributes to the stability of agroecosystems. Therefore, the main goal of the current study was to isolate associative to Triticum aestivum L. bacteria from the southern chernozem (Haplic Chernozems), which was sampled in the steppe zone of the Crimea. The methodical approach was used to select associative microorganisms for a specific plant species. The number of microorganisms of the main ecological-trophic groups for three varieties T. aestivum were determined. The maximum number of rhizosphere microorganisms was identified for the Ermak variety, as well as the number of morphotypes isolated from the apical part of the root. As a result of the research, six strains of associative bacteria were obtained. They increased the seed quality of the studied varieties by 5% and the biomass of the seedlings by 80%. Identification by the 16S rRNA gene showed their belonging to different bacterial genera. Thus, the quantitative composition of the chernozem southern of the rhizosphere of three varieties of T. aestivum was determined. Five strains of associative bacteria promising for further biotechnology of the agrocenosis rhizosphere were isolated.

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High yields of winter barley significantly depend on the elements of cultivation technology, among which seeding rate is of considerable importance. The aim of the current research was to identify the optimal seeding rate for winter barley in the current climatic conditions of the steppe zone of the Crimea. Winter barley variety ‘Buran’ served as a material of this study. In the course of the research we studied five variants of seeding rate – 1.0; 2.0; 3.0; 4.0; 5.0 million seeds per hectare. The experiments were carried out in the central steppe zone of the Crimea in 2018-2020 according to the methods of the State variety testing of agricultural crops. The first year of research was favourable in climatic conditions; the second one – unfavourable during the entire growing season. The survey highlighted some key points: the seeding rate influences the main components of winter barley yield – plants (stems) density and productivity of the ear. Over two years, an increase in the seeding rate increased plant density on average from 229 to 465 plants per m2. Ear productivity (grain weight per ear), on the contrary, decreased from 2.5 to 1.3 g. The yield of winter barley depended on the weather conditions of the year and, on average, reached 5.76 t/ha in 2019 and 3.41 t/ha in 2020 (which is 41 % less than in 2019). In 2019, at a seeding rate of 1.0 million/ha, a minimum yield (4.71 t/ha) was obtained. At other seeding rates, the yield of winter barley was statistically equivalent: 2.0 million/ha – 6.07 t/ha; 3.0 million/ha – 5.99 t/ha; 4.0 million/ha – 5.96 t/ha; 5.0 million/ha – 6.11 t/ha. In 2020, seeding rate did not have any effect on the yield of winter barley. It varied from 3.23 to 3.52 t/ha and was within the experimental error. The dependence of the indicators of grain quality on the seeding rates was noted only in 2020 for 1000-grain weight, which was significantly higher at seeding rates of 1.0 and 2.0 million/ha (36.8 and 36.7 g, respectively) compared to other studied ones. According to the efficiency of seed reproduction, the variants with the minimum seeding rates (1.0 and 2.0 million/ha) were the best. The rate of reproduction in these cases was 91 and 55, respectively.

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Pre-sowing inoculation with strains of associative bacteria is one of the promising methods for increasing the productivity of agricultural crops. These microorganisms are able to stimulate the growth processes of plants, improve their mineral nutrition, increase phytoimmunity and resistance to adverse factors. The aim of the research is to study the influence of strains with a high associative potential to Triticum aestivum L. on the microbiocenosis in the rhizosphere of soft wheat of several varieties grown on chernozem southern. The studies were carried out in 2018–2020 using three varieties – ‘Ermak’, ‘Bagheera’, ‘Lydia’. The experiments were laid on plots (accounting area – 25 m2) in systematic design, replicated four times. The climate of the study area is characterized as arid (steppe). Inoculation was carried out before wheat seeds sowing; option without treatment served as a control. Sampling was carried out in the most active phase – flowering (in May 2019 and 2020). In the course of the research, we found that changes in the number of microorganisms of various ecological-trophic groups of chernozem southern in the rhizosphere of wheat occur under the influence of bacterial strains associative to T. aestivum. Wheat variety ‘Bagheera’ was found to be the most responsive to seed bacterization; the average yield increase over two years of research was in the range of 0.2-0.4 t/ha or 5-10%. Calculation of coefficients and indices indicating the direction of mineralization processes in the soil made it possible to establish that inoculation promotes their activation. The results of the correlation analysis based on two-year data obtained after studying three varieties of winter wheat showed that the number of bacteria of the genus Azotobacter has the greatest influence on the yield – the correlation index is 0.81 at p <0.05.