Nitrogen fixation capacity of Azotobacter spp. strains isolated from soils in different ecosystems and relationship between them and the microbiological properties of soils.

The objectives of this study were to count and culture Azotobacter spp. in sampled soils, to determine the nitrogen (N) fixing capacity byAzotobacter spp. in pure culture and different soils, and to explore the relationships between N fixation capacity of Azotobacter spp. and microbiological properties of soils in Northern Anatolia, Turkey. Statistically significant relationships were found between the population of Azotobacter spp. in soils and microbial biomass C (Cmic), dehydrogenase (DHA), beta-glucosidase (GA), alkaline phosphatase (APA) and arylsulphatase (ASA) activities. However, relationships between the population of Azotobacter spp. and basal soil respiration (BSR), urease (UA) and catalase (CA) activities were insignificant. The N fixation capacities of native 3 day old Azotobacter chroococcum strains added to Ashby Media varied from 3.50 to 29.35 microg N ml(-1) on average 10.24. In addition, N fixation capacities of Azotobacter spp. strains inoculated with clayey soil, loam soil, and sandy clay loam soil during eight week incubation period were 4.78-15.91 microg N g(-1), 9.03-13.47 microg N g(-1) and 6.51-16.60 microg N g(-1), respectively. It was concluded that the most N fixation by Azotobacter spp. was in sandy clay loam soils.