The present study was conducted to investigate the possibility of using iron waste along with Thiobacillus bacteria to supply soybean iron requirement in a calcareous soil. In vitro, two strains of Thiobacillus thiooxidans (T. thiooxidans) and Thiobacillus ferrooxidans (T. ferrooxidans) have been investigated for their bioleaching potential from mill scale and pyrite in in the presence and absence of sulfur. In a greenhouse experiment, the effect of iron sources (control, ferrous sulfate, mill scale, and pyrite) and bacterial inoculation (T. thiooxidans, T. ferrooxidans, and simultaneous application of two bacteria) on iron uptake by soybeans was investigated. In laboratory experiment, the effect of T. ferrooxidans on iron bioleaching from the studied iron waste was greater than T. thiooxidans. T. ferrooxidans was more effective to enhance the iron dissolution from pyrite than mill scale. The application of sulfur increased the bioleaching efficiency. In the greenhouse experiment, inoculation with T. thiooxidans caused a significant increase in shoot iron concentration of soybean compared to control only in the application of pyrite, while T. ferrooxidans significantly increased iron uptake by soybean in the application of all iron sources as well as control treatment. The highest shoot iron concentration of soybean was obtained in simultaneous application of two bacteria species. While the addition of the mineral and waste iron components did not impact on iron uptake by soybeans, soil inoculation with T. ferrooxidans and simultaneous application of T. ferrooxidans and T. thiooxidans had a significant effect on iron biofortification in soybean.

Keywords