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Effect of Fe:ligand ratios on hydroponic conditions and calcareous soil in Solanum lycopersicum L. and Glycine max L. fertilized with heptagluconate and gluconate.

BACKGROUND
The environmental risk of synthetic chelate application promotes the implementation of biodegradables complexes to correct Fe-deficiency in plants. In this paper, the Fe oxidation state, the Fe:ligand ratio and molecular weight distribution for heptagluconate (G7) and gluconate (G6) are consider as key factors for the complexes efficacy as fertilizes. Complexes with different Fe:ligand ratios were prepared and analyzed by gel filtration chromatography (GFC). The ability of Fe:ligand ratios to provide Fe to tomato in hydroponics and soybean in calcareous soil was tested and compared to synthetic chelates (Fe3+ :HBED and Fe3+ :EDTA).


RESULTS
The G7 presented a higher capacity to complex both Fe(II) and Fe(III) than G6, but the Fe(II) complexes show low stability at pH 9 and oxidation in solution. GFC demonstrated the polynuclear nature of the Fe3+ :G7 at various ratios. The effectiveness of the Fe fertilizers depend on the Fe3+ :ligand ratio and the ligand type being the Fe3+ :G7 (1:1 and 1:2) the most effective. The Fe3+ :G7 (1:1) also presented a better response for the uptake of other micronutrients.


CONCLUSION
The Fe3+ :G7 molar ratios have shown to be critical for the Fe plant uptake under hydroponic conditions and calcareous soil. Thus, the Fe3+ :G7 at equimolar ratio and 1:2 molar ratio can be an environmentally friendly alternative to less degradable synthetic chelates to correct Fe chlorosis in strategy I plants. This article is protected by copyright. All rights reserved.