Distribution and Abundance of Azotobacter in Wheat Fields of Bangladesh

The distribution and abundance of Azotobacter as well as heterotrophic bacteria in root, rhizosphere soil and non-rhizosphere soil samples from various wheat fields of four different areas under three districts were investigated in this study. The potential for nitrogen-fixation of five Azotobacter isolates was also detected. All samples tested were positive in their capacity to harbouring Azotobacter with a range of 26-100%. The population of heterotrophic bacteria ranged from 2.1 x 107 to 1.2 x 108 cfu/g sample. Ranges of total number of Azotobacter in different samples were 5.2 x 104 to 7.2 x 104 cfu/g, 17.2 x 104 to 25.5 x 104 cfu/g, and 12.4 x 104 to 16.7 x 104 cfu/g respectively for root, rhizosphere soil and non-rhizosphere soil. A positive correlation was found in Azotobacter colonization between root and rhizosphere, but it was negative in case of the population between heterotrophic bacteria and Azotobacter in rhizosphere. The highest amount of N was found to be fixed by the isolate M1 and the lowest by the isolate M4 and it was respectively 9.26 and 5.45 mg N/g substrate. In terms of the capacity to fix nitrogen in laboratory condition the five isolates of Azotobacter could be arranged as M1> M3 > M5 > M4 > M2. Keywords: Azotobacter, Wheat field, Nitrogen fixing potentialDOI: http://dx.doi.org/10.3329/bjm.v24i2.1262