Evaluation of a non-aseptic stepwise culture technique with various carbon sources for nitrogen-fixing bacteria propagation

The reliance on urea fertilizers as nitrogen sources is gradually being replaced by biofertilizers containing nitrogen-fixing bacteria. However, the higher cost of biofertilizers compared to urea remains a barrier for farmers. A potential solution for farmers is to independently produce nitrogen-fixing bacteria cultures using a simple, non-aseptic culture technique. This study evaluates this technique for propagating nitrogen-fixing bacteria. It examines the effects of alternative carbon sources, such as cane sugar and white vinegar, to replace malic acid in Nfb medium. Soil samples, serving as bacterial sources, were inoculated into liquid Nfb medium, and subcultured for six stages. The most probable number (MPN) of nitrogen-fixing bacteria and medium pH were monitored at each stage. The results indicate that white vinegar supported the highest bacterial cell density, reaching 6.3 × 1010 MPN by the fifth culture stage. The increase in medium pH to an alkaline range suggests elevated ammonium concentrations, which are beneficial as a nitrogen source for plants. The culture technique demonstrated promising results and holds potential for practical application by farmers in propagating nitrogen-fixing bacteria.