Effect of Azotobacter chroococcum on sugar beet and microbial activity of rhizosphere

In sugar beet production, one of the most important factors that affect the yield, apart from genetic properties, is the use of mineral fertilizers. Considerate amounts of mineral fertilizers are used in sugar beet production. However, if agroecological conditions are not optimum, mineral fertilizers cannot be completely absorbed, which may lead to soil contamination. Therefore, research has been focusing on ways of using atmospheric nitrogen by means of nitrogen-fixing bacteria. Numerous researches have proved that one part of mineral fertilizers can be replaced by biological nitrogen. The aim of this research was to determine the effect of genotype, azotobacter and the amount of mineral fertilizers on the root yield of sugar beet and on the microbiological activity of the sugar beet rhizospheric soil. Three hybrids of sugar beet were used during the two years of the research. The seed of the hybrids was inoculated with three strains of azotobacter. Various amounts of NPK were used (0;30;60;90 kg/ha). At the end of the vegetation period, the following were determined: root yield, total number of bacteria, number of azotobacter, oligotrophic bacteria, ammonifiers, fungi, and actinomycetes in soil. Dehydrogenase activity was measured. The results were processed statistically (analysis of variance for factorial trials) and the effect of the factors was determined upon the expected mean square values. The yield was mainly affected by the amount of mineral fertilizers. However, the effect of mineral fertilizers was different with different inoculation treatments. The effect of the examined factors was dependant upon genotype, amount of mineral fertilizers, inoculation and the year of trials. The interaction between genotype, mineral fertilizers, inoculation and the year of trials was the factor that had the greatest effect on the number of almost all the examined soil microorganisms. U proizvodnji secerne repe za postizanje visokih prinosa, pored genetskih svojstava sorti, vazan faktor je i primena mineralnog djubriva. U ovoj proizvodnji koriste se znacajne kolicine mineralnog djubriva. Medjutim, u slucaju da agroekoloski uslovi nisu optimalni za valjano iskoriscenje unetog djubriva ono nece biti iskorisceno, te moze uticati na zagadjenje zemljista. Zato su vec duzi niz godina istrazivanja usmerena u pravcu iznalazenja mogucnosti koriscenja atmosferskog azota posredstvom bakterija azotofiksatora. Mnogobrojnim ispitivanjima utvrdjeno je da deo mineralnog azota