Nano- and Pheroid technologies for development of foliar iron fertilizers and iron biofortification of soybean grown in South Africa

Background: Foliar iron (Fe) fertilization of crops may increase Fe concentrations in edible portions of plants and improve yield in soils with low available Fe. However, the role of foliar Fe fertilization in increasing seed Fe has not been studied in soybeans (Glycine max). In this study, the Pheroid (R) nutrient delivery technology was combined with FeSO4 or nanostructured FePO4 to develop potential new Fe foliar fertilizers. Eight different treatments including different combinations of FeSO4 and Pheroids were foliarly applied on field-grown soybeans in Northern Cape province in South Africa to investigate their influence on seed nutrient composition and yield. Results: Confocal and optical microscopy images indicate that FeSO4 or FePO4 was not entrapped in the Pheroids but formed separate precipitates. The average seed Fe of the non-treated plants was 56 +/- 3 mg kg(-1), and none of the treatments (including the positive controls, FeSO4 and FeSO4 with citrate) significantly increased seed Fe over the control. There was also no significant change in yield or seed Zn, P, protein, or phytic acid. Thus, Pheroids as well as FeSO4 are not suitable as delivery system for Fe to soybean seeds due to Pheroid incompatibility with FeSO4 and poor dispersibility of FePO4. Conclusions: Because none of the Fe treatments (including positive controls) affected seed Fe concentrations, foliar Fe application may not be effective to increase seed Fe in crops such as soybean that already have high native Fe.