Assessment of potassium releasing ability of some bacterial isolates in in-vitro condition and identification of efficient isolates

Potassium (K) is an essential macronutrient that plays an important role in the growth and development of plants. Throughout the present study the possibility of K-release from mica minerals was evaluated through the action of several bacteria isolated from rhizosphere samples of grasses. The experiment was conducted as a factorial one, based upon a completely randomized design of three replicates comprised of two factors including 8 isolates of bacteria and two sources of potassium mineral. Following isolation of bacteria from the plant roots through NFB medium, eight selected isolates were ultimately used for the final experiment. Potassium release capability of these isolates was assessed using liquid Aleksandrov culture medium. Acid washed pretreated minerals, as a source of potassium, were added to 30 ml of Aleksandrov medium. Following incubation for one week at 26 °C and shaking at 120 rpm, released K in supernatant was assessed through flame photometer. The highest K release on the average was obtained by the isolate Az-8 (11.16 mg/l) and it was revealed that this bacterium was more efficient in releasing K from biotite than from muscovite, and the lowest rate of K release was obtained by Az-15 (2.8 mg/l). The results also revealed that K released from biotite exceed muscovite when the two types of mica compared. Among the bacterial isolates Az-8, Az-12 and Az-19 showed great potential for K release and their molecular (16S rDNA) and biochemical identification revealed that Az-8, Az-12 and Az-19 belonged to Pseudomonas genus. According to the promising results of in-vitro assays, inoculation and application of these efficient isolates will be recommended in greenhouse and field tests with different crops.