The inoculation of the legume seed material with active nitrogen fixing bacteria strains before sowing has a significant role for the increase of the legume yield. Inoculation can improve crop yields in cases where appropriate rhizobia are not present in the soil or the soil contains a significant proportion of non-nodulating or ineffective nitrogen-fixing strains. The aim of the investigation was to detect the effectiveness of Rhizobium leguminosarum strains in field beans at different soil microbiological activity. The experiment was conducted at the Institute of Soil and Plant Sciences of the Faculty of Agriculture of the Latvian University of Agriculture from the 5th of June till the 17th of October 2008. The field bean (Vicia faba. L) cultivars - 'Ada', 'Lielplatones', Rhizobium leguminosarum bv. vicia strains No. 110; 408; 501 and 2 types of soils (with different microbiological activity) were used in vegetation pot experiment. The highest shoot dry matter was observed in cultivars cultivated in soil with higher microbiological activity. The highest pod dry matter was observed in cultivars cultivated in soil with higher microbiological activity. The highest total nitrogen amount was in field beans cultivated in soil with lower microbiological activity. Rh. leguminosarum strain resistance to streptomycin decreases with the plants age, from anthesis forward in both soil types and both cultivars. The fingerprinting showed significant difference between Rh. leguminosarum strains.

Studies were conducted at the experimental station of the Stavropol State Agrarian University on leached chernozem, powerful, low-humus heavy loam on loess-like loam in 2017. The goal was to study the effect of the introduction of rocks rich in chemical composition (limestone-shell rock, apatite and phosphogypsum), both separately and jointly, on the microbial phase of the soil. The determination of the number of microorganisms was produced on dense nutrient medium by direct counting of colonies. It was found that the amount of ammonifiers under the control was 37 ml CFU gE−1 (colony-forming units), increasing 1.3–1.5 times with separate use and 2.5–3 times with the joint use of rocks. Similar changes were observed with respect to the number of nitrifiers and aerobic nitrogen fixers of the type Azotobacter. The number of cellulose-depleting microorganisms in the remineralization variants reached 220,00–230,00 CFU gE−1 compared to 115,00 CFU gE−1 under the control. With the introduction of separate rocks, there was a decrease in the occurrence of pathogens, while with a joint introduction they were not detected. The frequency of occurrence of toxin formers, such as Aspergillus and Penicillium, reached 100% at the control and decreased by 20–40% at the experimental variants. It was revealed that the introduction of shell limestone, apatite and phosphogypsum had an effect on the increase in the number of soil microbiota of various physiological groups. Among the fungal microflora, the number of pathogens and toxin formers decreases and the number of pathogen antagonists increases.