Microbiological Activity of Chernozem in the Combined Use of Potassium Chloride with Nitrogen Fertilizers

In order to assess the possible toxic effect of potassium chloride used in conjunction with mineral nitrogen fertilizers the authors studied the structural and functional components of the microbial complex of chernozem, in particular, its prokaryotic component. The object of research was soil samples of typical chernozem, selected from the vegetation experience with variants with the introduction of nitrogen-phosphorus and ni-trogen-phosphorus-potassium fertilizers. To obtain a stable effect of easily soluble salts on the microbial community of the soil, long-term composting of soil samples was carried out with alternating cycles of moistening and drying of the soil. During the first two years of composting, the researches detected the suppression of carbon dioxide emissions; however the suppression leveled out only 5 years later. The initial reduction in carbon dioxide emissions, as well as denitrification activity, reached twofold values. The negative effect was manifested when the content of chlorides and nitrates in the soil was significantly lower than the gradation established for slightly saline soils. Prolonged composting of samples of fertile chernozem under the action of potassium chloride led to a decrease in the number and biomass of the metabolically active prokaryotic complex, which confirms its toxic effect on the microbial community of the soil. The representatives of the prokaryotic complex that are resistant and sensitive to the increased content of chlorides and nitrates in the soil have been identified. Among the representatives of the Bacteria domain, almost all were sensitive, with the exception of two phyllum Firmicutes and Verrucomicrobia. For some representatives of the phylogenetic group Actinobacteria, sensitivity to chlorine ions is confirmed at the generic level (Streptomyces and Micromonospora). For the Archaea domain, representatives of the Euryarchaeota phylum are identified as the most resistant to the presence of chlorides. Thus, the suppression of the microbiological activity of chernozem during the introduction of potassium chloride explains the previously identified decrease in the availability of nutrients for plants.