Potassium solubilising bacteria (KSB) isolated from rice paddy soil: from isolation, identification to K use efficiency

Abstract

The present study was intended to isolate potassium-solubilizing bacteria (KSB) from paddy rhizosphere soil. The isolates were obtained from 40 rice paddy fields across Mazandaran province in northern Iran and screened for their K-solubilizing ability on modified Aleksandrov agar medium. The three selected isolates which showed the best solubilisation of potassium were identified using molecular marker 16S rDNA sequencing. The isolates were identified as Pantoea agglomerans, Rahnella aquatilis and Pseudomonas orientalis. From the flame photometry results, the amounts of potassium released by the isolates from mica at 21st day of incubation were 35.36, 76.04 and 56.58 μg ml−1, respectively. The estimated optimal growth temperature (Ts) were 26.38, 29.17 and 26.80 °C based on segmented model analysis. The pH values of the culture medium with ranges from 6.75–7.26, had a more positive effect on the solubilization of potassium-bearing minerals. The pot experiment results showed that the inoculums of all three KSB enhanced the amount of grain yield and K uptake compared to the control treatment (without K fertilizer). Values were higher when KSB inoculums were used with ½ K chemical fertilizer (47.5 Kg/ha). Bacterial inoculums also increased K use efficiency (AE, PE, APE, ARE and UE) in plants. In conclusion, these findings have successfully demonstrated the effectiveness of locally isolated PGPR with multiple beneficial characteristics such as K solubilizing, IAA production and tolerance to different environment stresses. Therefore, they can be used as biofertilizers to enhance the availability of potassium in the soils and to improve the growth and yield of rice.