The effect of different doses of herbicide nicosulfuron on morphology of colony and survival of azotobacter

Azotobacter belong to the section of Qramm negativ rod to oval shape bacteria, fam. Azotobacteriaceae. They are non - sporogenic, aerobic heterotrophic, free living M - fixing bacteria (diazotrophs). They presence is greater in the rizospheric soil than in bulk soil (Mrkovacki etal., 2006). In our climate region azotobacter is present from few hundred to ten thousand cells per gram of dry soil, and they can fix, in the field condition, 20 60 kg n ha-1 per year (Mrkovacki et al., 1987). The aim of the experiment was to investigated the effect of different doses of herbicide nicosulfuron (Motivell) on the morphological changes and survival of four azotobacter strains isolated from four different typs of soil. Azotobacter strains in pure culture were taken from the colection of laboratory of Microbiology, and they were isolated from four different typs of soil: chernozem - strain Ac006, humogley - strain ARC003, pseudogley - strain APS001 and luvisol strain ARudo004. Investigation was split in two parts: evaluation of morphological attributes of colonies of four azotobacter strains prior to herbicide application and enumeration of effect of different herbicide doses on surviving (number) and morphological changes of azotobacter colony. All applied doses of herbicide nicosulfuron significantly decreased the number of azotobacter strains isolated from chernozem (strain Ac006) and humogley (strain ARC003). Five and ten fold doses, than recomanded doses, enhance the survivel of strains isolated from pseudogley (APS001) and luvisol ARudo004). Both doses caused the morphological changes of azotobacter colony. Colonies were smaller with thiner profile and stronger pigmentation. All investigated strains had weak survival in variants where the number of cells were lower at the begining.