Quantification of Indigenous Rhizobial Populations Associated with Pea Nodulation in Kumaon Region of North-western Himalayas

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The purpose of this study was to explore the diversity of native rhizobial populations in pea-cultivating regions of the Kumaon area in the north-western Himalayas and their role in biological nitrogen fixation (BNF). The research employed completely randomized design (CRD), involving the collection of soil samples from 12 locations to analyze rhizobial populations, soil physicochemical properties, and their effects on pea nodulation and nitrogen accumulation. A positive correlation was observed between soil organic carbon (OC) levels and the most probable number (MPN) of rhizobia, with higher OC supporting greater rhizobial growth and BNF. Sites such as Daranti and Khamaria, with elevated OC levels, exhibited higher rhizobial populations and enhanced nodulation, while regions with lower OC, such as Chafi and Sui, showed reduced activity. Daranti recorded the highest rhizobial count 10,000 g⁻¹ of soil, and Timiladiggi demonstrated superior nitrogen fixation efficiency (18.01 mg plant⁻¹ BNF). These findings suggest the potential for isolating and using efficient rhizobial strains, such as those from Timiladiggi, as inoculants to improve BNF in less fertile areas. The study also identified climatic influences on soil properties, with cooler, high-altitude regions promoting greater OC accumulation and rhizobial activity. These results emphasize the importance of utilizing efficient rhizobial strains and enhancing soil OC to boost legume productivity and support sustainable agriculture in diverse agroclimatic zones. Future research should focus on metagenomic analyses to characterize the genetic diversity of native rhizobia and uncover their functional traits.