Purpose The aim of this work was to test the hypothesis that Fe mining sub-products and thiols can alleviate a moderate Fe-deficiency in the Strategy I species soybean (Glycine max) grown in a calcareous soil in greenhouse conditions. Methods Combinations of three Fe sources [Fe(III)-EDDHA and two Fe mining sub-products, one containing Fe oxides and FeS2 and the other Fe oxides], and three thiols (glutathione, dithiothreitol and thiophenol) were applied in solution to the soil, three times in a 55 day period, and different parameters related to Fe deficiency were measured. The thiol-mediated solubilization of Fe from the Fe mining sub-products was assessed by measuring in the solution total Fe and the reducible Fe pool using an Fe(II) chelator. Results Application of Fe-EDDHA, the two Fe mining sub-products and the three thiols relieved the Fe deficiency symptoms to different extents, increased the Fe concentrations and contents throughout the plant and changed the redox state of leaves and roots, as judged from the changes in reduced and oxidized glutathione, ascorbate and antioxidant enzymes. When using Fe(III)-EDDHA, the addition of thiols led to a better leaf regreening. However, the addition of thiols did not cause further regreening in the case of the Fe mining sub-products, in spite of being able to solubilize Fe from them. Conclusion Application of Fe-mining sub-products, thiols and the combination of Fe(III)-EDDHA and thiols could be used to alleviate moderate Fe deficiency in G. max grown in a calcareous soil.

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