Indigenous plant growth-promoting rhizobacterial consortia greatly reduces fertilizer need for tea nurseries: Characterization and evaluation

A study was conducted to characterize plant growthpromoting rhizobacteria (PGPR) of tea [Camellia sinensis (L.) O. Kuntze] and to investigate the potential of using them to enhance growth and nutrient uptake of tea plants, and also to reduce the use of chemical fertilizers in tea nurseries in the mid-country of Sri Lanka. Nitrogenfixing Azospirillum sp. (AZO) and phosphate solubilizing bacteria (PSB) isolated from the rhizosphere of tea grown in three main soil series i.e. Kandy, Matale and Ukuwela in Sri Lanka, were screened in an in vitro study. Soil series specific dual inoculants were formulated using the most effective strains of N2 fixer and PSB obtained from each soil series, and they were tested in tea nurseries having respective soil series. In addition, a common consortium was tested across all the three soil series. Dual inoculants were tested along with a modified T 65 fertilizer mixture composed of ½ of N and P replaced with Eppawala Rock Phosphate (ERP) in place of Di Ammonium Phosphate (DAP) in recommended T 65 fertilizer and compared with two non-inoculated controls; modified T 65 fertilizer and T 65 recommended fertilizer, each with ten replicates. Plant growth measurements were taken and N and P uptakes were measured. Application of series-specific consortium to nursery tea plants raised in soil belonging to Ukuwela soil series along with modified T 65 fertilizer mixture improved dry matter contents (12.86 g/plant) and total N and P uptake (786 mg/plant and 155 mg/plant, respectively) compared to that of recommended fertilizer treatment (dry matter contents; 13.24 g/plant, N uptake; 727 mg/plant and P uptake; 166 mg/plant). Results indicated that a 50% reduction of N and replacement of imported DAP with locally available ERP in the present recommendation for tea nursery mixture (i.e. T 65) is possible with the application of dual inoculants formulated with series-specific strains.