Tea yield maintained in PGPR inoculated field plants despite significant reduction in fertilizer application

A study was conducted to formulate dual plant growth promoting rhizobacteria (PGPR) inoculants, indigenous to each soil series where fields were located, to enhance growth and yield of tea (Camellia sinensis (L.) O. Kuntze), managed with low fertilizers inputs. Field experiments were conducted in five different locations with both early and later stages of mature tea fields representing three soil series Le Kandy, Matale and Ukuwela. Soil series specific dual inoculants (i.e., Azospirillum sp. + Rhodococcus sp. for Kandy, Azospirillum sp. + Microbacterium sp. for Matale and Azospirillum sp. + Bacillus cereus for Ukuwela soil series) were tested in fields having respective soil series. In addition, a common consortium (Azospirillum sp. + Bacillus cereus) was tested across all the three soil series. They were tested along with a modified VP/UM 910 fertilizer mixture composed of 2/3 N and 1/2 P of the recommended application, and compared with three non-inoculated controls: an untreated control, a non-inoculated modified VP/UM 910 fertilizer control, and the VP/UM 910 recommended dose of fertilizer control, each with three replicates. Yield records were maintained and soils and leaf N and P contents were assessed after one year. The made tea yield of each soil series, with its soil series specific dual inoculants, conducted in four locations representing Kandy and Matale soil series, varied from 2521 to 2681 kg ha(-1) yr(-1) and remained comparable to fields with the recommended fertilizer treatment (2491-2697 kg ha(-1) yr(-1)). Comparable yields to recommended fertilizer treatment due to series specific dual inoculant could also be observed in the location representing Ukuwela soil series. Results indicated that a 1/3 reduction of N and 1/2 reduction of P from the recommended fertilizer dosage VP/UM 910 are possible with application of dual PGPR inoculants formulated with soil series specific strains.