Microorganisms are a heterogeneous group of organisms whose enzymatic systems take 60-90% of the total metabolic activity in soil. Dominance of certain groups of microorganisms affects the processes of soil synthesis and decomposition and it determines the quality of soil and its applicability for the production of safe food. The nonsymbiotic nitrogen fixer Azotobacter is an obligate aerobe living in the soil, the rhizosphere and the plant root. The ability of various strains to fix atmospheric N positively affects plant growth and yields. In this study we have determined the abundance of azotobacter, fungi, actinomycetes and the total number of microorganizms in sugarbeet rhizosphere. Simultaneously we studied the effect of application of nitrogen fertilizer, manure and harvest residues. Samples of rhi-zosphere soil were taken three times in the course of growing season (May, July, September) the ex-periment included two variants (inoculated with azotobacter and noninoculated) in four fertilization levels (nonfertilized control, 50, 100, 150 and 200 kg N/ha), in five replication. The results of the stu-dy for all four fertilization types and all four levels of added N showed that azotobacter abundance was higher in inoculated treatments than unino-culated ones. The highest percentage increases of azotobacter numbers, total microbial abundance and number of fungi and actinomycetes were recor-ded in the inoculated treatments with barnyard ma-nure, NPK fertilizer, and barnyard manure plus harvest residues, respectively. In inoculated and uninoculated treatments alike, the highest azoto-bacter abundance was found in the treatment with no N added, while the lowest was recorded in the treatment with 200 kg N/ha added. The highest total microbial abundance was obtained with 100 kg N/ha in inoculated treatments and 200 kg N/ha in uninoculated ones.

soil; microorganisms; rhizosphere; sugarbeet

Presentation: oral