Evaluation of Biological Nitrogen Fixation by Azotobacter Isolates in Solid and Liquid LG Medium by Kjeldahl method

There are different methods for evaluation of the biological nitrogen fixation, which they are mainly included acetylene reduction assay, labeled nitrogen and nitrogen difference methods. Accuracy and sensitivity of these methods are different, but applying of some of these methods isn’t possible in all laboratories, so it cause the use of less accurate methods for evaluation of the nitrogen fixing content. Therefore, this article was aimed to investigate the content of nitrogen fixation (NF) of some bacteria isolates including Azotobacter using the Kjeldahl method. A total of 22 bacteria isolates were used and evaluated. The isolates were cultured in solid and liquid LG media and the content of the nitrogen fixation was measured in solid and pellet of liquid culture. According to the results of digestion, distillation and titration (Kjeldahl) of the cultured sample in the solid medium, the maximum nitrogen-fixation content 261.10 and 258.64 µg/g were found in 14SP- Ш and 14SP2-1, respectively. The highest nitrogen-fixation content in liquid culture medium was obtained in 14SP-I (80 µg/ml). The results of liquid and solid culture media indicated that the maximum nitrogen in14SP-I and 14SP2-1 isolates belonged to the Azotobacter chroococcum, Pseudomonas 35SP-2, and Achromobacter 14SP- Ш. The results of NF in both solid and liquid cultures showed a good correlation (r=0.69**). It seems that the method can be used for screening the efficient nitrogen fixing bacteria, although this is not so a precise method. 14SP-Ι, 14SP-Ш, 14SP2-1, 35SP-2 and 44SP-2 strains can be suggested among the isolates for the greenhouse and farm experiments.