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

The structural and functional components of the microbial complex of chernozem, in particular, its prokaryotic component, were studied in order to assess the possible toxic effect of potassium chloride applied together with mineral nitrogen fertilizers. Soil samples of typical chernozem were taken from the experimental plots with application of nitrogen-phosphorus and nitrogen-phosphorus-potassium fertilizers. To obtain a stable effect of soluble salts on the microbial community of soil, long-term composting of the samples with alternating drying and moistening cycles was performed. During the first two years of composting, the r the suppression of carbon dioxide emission was detected. It was completely leveled out only five 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 level established for slightly saline soils. Long-term composting of the samples treated with potassium chloride led to a decrease in the number and biomass of the metabolically active prokaryotic microorganisms, which confirmed its toxic effect on the microbial community of the soil. Representatives of the prokaryotic complex tolerant and sensitive towards the increased concentrations of chlorides and nitrates in the soil were identified. Almost all representatives of the Bacteria domain, except for Firmicutes and Verrucomicrobia phyla, were sensitive to these salts. Sensitivity to chlorine ions was confirmed at the generic level (Streptomyces and Micromonospora) for some representatives of the phylogenetic group of Actinobacteria. For the Archaea domain, representatives of the Euryarchaeota phylum were identified as the most tolerant towards the presence of chlorides. Thus, the suppression of the microbiological activity of chernozem under the impact of potassium chloride explains the earlier identified decrease in the availability of nutrients.