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Distribution and Abundance of Azotobacter in Wheat Fields of Bangladesh

Muhammad Ali Akond
Department of Botany, Jahangirnagar University, Savar, Dhaka 1342, Bangladesh

Sanzida Mubassara
Department of Botany, Jahangirnagar University, Savar, Dhaka 1342, Bangladesh

M Motiur Rahman
Department of Botany, Jahangirnagar University, Savar, Dhaka 1342, Bangladesh

Abstract/ Executive Summary:

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 potential

Location: Ten various wheat fields of four different collection areas such as Manikganj, Dhamrai, Gajipur and Savar

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Bio fertilizer

Objectives:

To study the distribution and abundance of Azotobacter in some wheat field soils of Manikganj, Dhamrai, Gajipur and Savar, Bangladesh.

Methodology:

Samples of non-rhizosphere soil, rhizosphere soil and wheat plant were collected from ten various wheat fields of four different collection areas such as Manikganj, Dhamrai, Gajipur and Savar. Rhizosphere soil was collected from the rhizosphere region of the plants at the depth of 2-3 cm and non-rhizosphere soil was also collected from a nearby place of the field at the same depth. The soil pH was determined by an electric pH meter. For this purpose a suspension with a soil:water ratio of 1:2.5 (w/v) of each collected sample was used. One gram of each soil and root sample was used for the purpose of isolation of Azotobacter. Roots were washed first with tap water and then with distilled water twice. The pieces of roots were taken in a sterile mortar and macerated with the help of a sterile pestle. Then 10 ml of sterile distilled water was added to prepare a suspension of root sample. Suspension for soil sample was made using the serial dilution method. Plates of LG agar medium were inoculated with the suspension of root and soil samples by streaking method. Plates were incubated at 30^oC for 5 days. Development of flat, soft, milky and mucoid colonies was the indication for the growth of Azotobacter. For enumeration of Azotobacter suspension of both root and soil samples were prepared using serial dilution method and plated on LG agar medium. After incubation 5 days at 30^oC, the colonies appeared on the agar plates were counted. Nitrogen fixation was determined in terms of the quantity of nitrogen gained in 5-days-old culture of each isolate developed in 50 ml LG broth medium. Nitrogen in culture was estimated by micro-Kjeldahl method.

Source of Information: Bangladesh J Microbiol, Volume 24, Number 2, December 2007, pp 151-153

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

It was found that the selected strains could fix nitrogen ranging from 5.45 to 9.26 mg N/g substrate by 5-days-old 25 ml culture. The strain M₁ could fix the highest amount of nitrogen (9.26 mg N/g substrate) and the strain M₄ fixed the least amount (5.45 mg N/g substrate). The present study showed that the isolates recovered from the wheat fields are of average standard in terms of their nitrogen fixing potential in the laboratory condition.

Knowledge Management: Journal