Foliar application of organic and inorganic iron formulation induces differential detoxification response to improve growth and biofortification in soybean

Foliar fertilization for biofortification is a targeted, economic and environment friendly approach rather than soil fertilization. In this study, we identified the appropriate growth stage(s) and right foliar iron (Fe) formulation in enhancing growth and Fe biofortification in soybean. In addition, we studied the physiological mechanism adopted by plants to endure foliar supplied Fe. For this purpose, a field experiment was conducted to evaluate various organic and inorganic Fe formulations such as Fe-citrate, FePO4, humic acid (HA)+Fe, HA alone and nano-Fe along with control (deionized water) in soybean (Glycine max var. DS-2614). Plants were sprayed at flowering (Set I), pod filling (Set II) and at both stages (Set III). Biomass and leaf area were significantly enhanced with application of Fe-citrate and FePO4 followed by HA+Fe. The yield traits (pod number, seed yield, test weight) significantly increased with HA+Fe and nano-Fe application. Enhanced Fe accumulation in seed was observed with HA+Fe followed by Fe-citrate and nano-Fe treatment. Foliar application of Fe at pod filling stage improved growth whereas yield and Fe fortification improved in Set III. This response may be attributed to enhanced activities of antioxidant scavenging enzymes and reduced lipid peroxidation in leaves treated with HA+Fe followed by FePO4. Results suggest foliar application of HA+Fe (organic Fe) and nano-Fe to be promising for soybean in improving growth and seed Fe content.