Changes in Soil Zinc Chemical Fractions and Improvements in Wheat Grain Quality in Response to Zinc Solubilising Bacteria

Abstract

This study was performed to investigate the impacts of two indigenous strains of zinc (Zn) solubilising bacteria on Zn fractionation in soil, Zn uptake and the molar ratio of phytic acid to Zn (PA/Zn) in wheat grain cv. Chamran. The experiment was implemented in a completely randomised factorial design that included the treatment of bacterial inoculation consisting of B0 (control), B1 (Bacillus megaterium), B2 (Enterobacter cloacae), B3 (a mixed inoculation of both bacteria), and ZnSO4 fertiliser at three application levels: Zn0 (control), Zn1 (5.1mgkg-1), and Zn2 (10.1mgkg-1). Bacillus megaterium was isolated from the rhizosphere of Zea mays, which can solubilise Zn and phosphate and produce auxin. Enterobacter cloacae, which had been isolated from sugarcane root, was screened qualitatively and determined to be the best isolate to solubilise Zn. The results indicated the maximum values of organically bound (2.08 mg kg-1) and exchangeable Zn (0.89 mg kg-1) in the Zn2B3 treatment. Also, the highest amounts of carbonate bound (9.25 mg kg-1), FeMn-oxides (10.70 mg kg-1), and residual fractions (16.17 mg kg-1) were recorded for the Zn2B0 treatment. The relative proportions of residual, FeMn-oxides, carbonate, organic, and exchangeable Zn fractions in Zn0B0 were 40.48, 29.2, 27.1, 2.18, and 0.84%, respectively. These proportions changed to 37.24, 29.51, 26.9, 4.3, and 1.75%, in the Zn0B3 treatment. Maximum values of Zn uptake and grain yield were associated with the Zn2B3 treatment, showing increases (compared to the control) of 214 and 46%, respectively. The lowest ratio of PA/Zn was obtained in the Zn2B3 and Zn2B2 treatments, which exhibited reductions of 31.38 and 30.86%, respectively, when compared to the control.