Assessment of Some Qualitative Characteristics of Common Biofertilizers in Iran

Abstract
The beneficial effects of biofertilizers can only be achieved if adequate quality control of biofertilizers is available. However, quality control assessment of four common types of biofertilizers in Iran including Barvar2, Biosuperphosphate, Nitroxin and Supernitroplus was the aim of this study. The targets of this research were counting viable numbers of microorganisms which present in the biofertilizers over the shelf life of the product, isolation and biochemical identification of isolates in each biofertilizer and determination of PGPR feauters. PGPR features of biofertilizares (5 treatments) such as phosphate solubilizing, potassium releasing ability, auxin and siderophore production were tested in a completely randomized design with three replications. Treatments were: control, Nitroxin, Barvar2, Biosuperphosphate and Supernitroplus. The results of counting of microbial viable cells in the general and semi-selective media indicated acceptable number of  viable cells in Supernitroplus and Barvar2 (10⁸ cfu/mL), respectively. The results of the identification and confirmation of isolates which used in the biofertilizers showed that two isolates (Ba1 and Ba2) exist in Barvar2, two isolates (Sn1 and Sn2) are in Supernitroplus, 4 isolates (Bio1-Bio4) and 5 isolates (N1-N5) are present in Biosuperphosphate and Nitroxin, respectively. Furthermore, the highest amount of phosphate solubility from tricalcium phosphate source were gained for Biosuperphosphate and Barvar2, with values ​​close to 400 and 350 mg/L respectively. Nitroxin and Barvar2 were successful in the production of auxin. All biofertilizers with an exception Bratvar2 were able to produce siderophore on CAS-agar medium. Although some quality characteristics of biofertilizers were determined in this study but identification of genus and species of bacteria which have been used in these biofertilzers and PGPR features of each isolate should be considered in the new researchs.