LAUSR

Nano-fertilization of agricultural systems is emerging as an innovative and unique strategy for agronomic fortification. In this study, a laboratory experiment was conducted to evaluate the physiological performance of soybean (Glycine max L.) exposed to either foliar or soil amendments of Fe2O3 nanoparticles (nFe2O3; 15, 30, and 60 mg/pot), fulvic acid-coated nFe2O3 (nFe2O3-FA; 60 mg nFe2O3/pot), and Fe-EDTA during an eight-week growing period. The experimental results demonstrated that none of the treatments produced toxicity stress or growth disorders. Amendments of nFe2O3 and nFe2O3-FA remarkably enhanced chlorophyll content, plant biomass, and root developmental indices. Fe-EDTA, a conventional fertilizer, did not provide satisfactory results compared with the other treatments. Regarding the supply of iron (Fe), foliar amendment provided 2–4 times higher shoot Fe concentration than soil application. Foliar amendments of nFe2O3-FA exclusively stimulated biological nitrogen fixation, which was primarily reflected in the formation of root nodules. This finding might be associated with the binary effect of the fulvic-Fe supply as well as enhanced potassium and zinc absorption in the plant than that of selective Fe penetration via negatively charged complexes. Further analysis of soil pH showed no evidence for facilitated Fe uptake via rhizosphere acidification. Conclusively, soybean responded better to the foliar amendment of nFe2O3-FA than nFe2O3 alone. This result suggests a novel perspective on the potential application of natural nanomaterial coating agents for nano-fertilization. From a practical perspective, it is necessary to consider the phosphorus (P) interaction and availability in the soil under nFe2O3 amendment, since the treatments substantially decreased P concentration in the soybean shoots, and thus a possible deficiency in plants under the critical pH value (below 6 and between 8–8.5) would be expected.