Population dynamics of Azotobacter chroococcum in sugarbeet rhizosphere depending on mineral nutrition

Population dynamics of Azotobacter chroococcum has been studied in the rhizosphere of a sugarbeet hybrid inoculated with Azotobacter strains 5, 8, and 14. Simultaneously we examined the effects of four levels of nitrogen fertilization (non-fertilized control, 50, 100, 150 and 200 kg N/ha) and the applications of manure and harvest residues. Samples were taken three times, in May, July and October. The experiment included inoculated and non-inoculated variants at all four levels of fertilization, in five replicates. Azotobacter populations were largest, in both non-inoculated and inoculated variants, at the beginning of the season (1st date) and they decreased subsequently. The inoculation of the rhizosphere of the variety Sara increased the number of Azotobacter in relation to the non-inoculated variant at all three dates. The highest increases were registered in the variants with NPK and NPK + manure (1st date) and in the variant with harvest residues and harvest residues + manure (2nd date). Inoculation increased the number of Azotobacter in sugarbeet rhizosphere at all four intensities of nitrogen fertilization. The increase was the highest in the variant with 100 kg N/ha. The increase was the lowest in the variant with 150 kg N/ha.