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ABSTRACT
Studying the ecological risk of the herbicides used in modern agriculture is very important for environment protection from pollution. Therefore investigations of herbicide effect on important for soil fertility and plant nutrition microorganisms is actual and necessary. An ecological assessment of two herbicides/gardian and pivot/was done by measuring the bacterial growth of non-symbiotic nitrogen fixing bacteria—Azotobacter chroococcum 18 and two strains of Azospirillum brasilense—Sp. 7 and Sp. 107. Inhibition of bacterial growth is observed and it depends on the herbicide used, its concentration and the bacterial strain. Three rates of herbicides were studied. Gardian inhibition on the bacterial growth varies from 22 % to 75%. The decrease of the size of bacterial colonies of A. brasilense Sp. 7, when the highest concentration is used is 75%; in case of A. brasilense Sp. 107 - it is 50%. In case of pivot application A. brasilense Sp. 107 is more resistant again/inhibition varies from 17% to 50%/; for A. brasilense Sp. 7 it is respectively 33% and 56%. In case of A. chrococcum the inhibition of the highest concentration of gardian is 56% and of pivot - 50%. The results show that gardian is more toxic than pivot as concerning the growth of the bacterial species studied.