Zinc-solubilizing Pseudomonas strains improve zinc nutrition of maize plants grown in sand amended with tire waste powder

The present study was conducted to investigate the potential of Zn-solubilizing Pseudomonas strains to release Zn from tire waste powder (TWP) in a liquid medium and soil. A pot experiment was also conducted to investigate the effects of TWP (as a Zn source) at four rates of 0, 9, 18 and 27 g TWP kg(-1) soil and Pseudomonas strains (Ctrl: without bacterial inoculation, or inoculated with B1: A5, B2: K5, B3: A2, B4: A11 or B5: D12 strain) on growth and Zn nutrition of maize. Fourteen bacterial strains were grown in liquid Pikovskayas (PVK) medium supplemented with TWP, and ten superior Pseudomonas strains with high Zn solubilization activities were selected for the subsequent Zn kinetics study. In the TWP-treated soil, the concentrations of DTPA-extractable Zn were significantly higher in inoculated treatments than those in the control treatment in all incubation times. Individual application of Pseudomonas strains or TWP treatments significantly increased the shoot biomass of maize plants. Furthermore, the combined application of Pseudomonas strains and TWP led to higher shoot Zn concentration of plants as compared to the individual applications. The highest shoot Zn concentration was observed with the use of 18 g TWP kg(-1) soil in treatment inoculated with B4 strain, which was 16.5-fold higher than that in the control. These findings indicate that co-application of effective Pseudomonas strains with TWP in soils can lead to higher Zn bioavailability for plants, i.e. indicating the potential of TWP as a slow-release Zn fertilizer for crops.