Phosphate solubilizing bacteria possess the ability to solubilize insoluble phosphate to soluble forms by enhancing the nutrient status of the soil. This process not only compensates increasing cost of phosphatic fertilizers but also minimizes the negative environmental impacts associated with the application of inorganic fertilizers. Phosphate solubilizing bacteria (PSB) were screened based on the size of a halo/clear zone around the colony (NBRIP agar plate assay) and by measuring solubilize phosphorous content (colorimetric method). The aim of this work was to assess the comparative reliability of quantitative and qualitative methods of isolation of phosphate solubilizing bacteria. Bacterial strains which showed very poor performance in qualitative method were proven to be good phosphates solubilizers in quantitative method and vice versa. Therefore, no positive relationship among the values obtained from qualitative and quantitative methods could be observed. Furthermore, qualitative method did not reflect the real ability of the phosphate solubilizing bacteria to solubilize insoluble phosphates. From the results of the present study, it can be concluded that isolation of efficient phosphate solubilizing bacteria through quantitative method could give better results than qualitative method.
Keywords: Bacteria, clear zone, isolation.