Alterations in mineral nutrients in soybean grain induced by organo-mineral foliar fertilizers

Chemical composition of soybean grain may be modified by application of foliar fertilizers. The aim of this study was to test the effect of different organo-mineral foliar fertilizers: Zlatno inje, Bioplant Flora, Algaren BZn, Zircon, as well as plant growth regulator Epin Extra, on potential availability of mineral elements (Mg, Fe, Mn and Zn) from grain of three commercial soybean varieties: ZP-015, Nena and Laura (variety lacking in Kunitz trypsin inhibitor). In addition, phytate (Phy) and β-carotene contents were determined. ZP-015 achieved the highest P, Mg, Fe, Mn and β-carotene contents. Laura had the highest Phy level, which might reflect the diminished availability of nutrients from grain. Compared to control, most of the applied fertilizers increased β-carotene and decreased Mn content in all three soybean varieties. Increase in β-carotene content was followed by increase in Fe content, mainly in grains with larger weight, as a part of improved yielding potential. Positive effect of Zircon application was evident on increased grain weight, and β-carotene and Fe content. These parameters together with the lowest values found for Phy/β-carotene and Phy/Mg ratios may explain the enhanced Mg and Fe bioavailability. On the other hand, positive effects of Epin Extra were mostly reflected by a decrease of Phy and an increase in Fe and Mn, thus becoming more bio-available. Accordingly, the organo-mineral foliar fertilizers based mainly on phenolic acids (Zircon) and bioregulator (Epin Extra) are to be recommended for soybean fortification.