Zinc oxide and ferric oxide nanoparticles combination increase plant growth, yield, and quality of soybean under semiarid region

Zinc (Zn) and iron (Fe) malnutrition are global health challenges that need immediate attention. Hence, to address these issues, a two-pronged approach involving the development and application of novel Zn and Fe products for crop fertilization may be a potential solution. Therefore, zinc oxide (ZnO) (∼13.2 nm) and ferric oxide (Fe₂O₃) (∼15 nm) nanoparticles (NPs) were synthesized and characterized. Seven nutrients treatments viz, control, ZnO- NPs (25 mg kg^-1), Fe₂O₃-NPs (25 mg kg^-1), ZnO + Fe₂O₃-NPs (25 mg kg^-1each), ZnSO₄ (55.8 mg kg^-1), FeSO₄ (60.4 mg kg^-1) and ZnSO₄+ FeSO₄ (55.8 and 60.4 mg kg^-1) were arranged in five-time replicated Completely Randomized Design model to test the effectiveness of ZnO and Fe₂O₃ NPs in two soybean cultivars over conventional zinc sulfate (ZnSO₄) and ferrous sulfate (FeSO₄) fertilizers. The results indicated that the photosynthetic rate (Pn) and chlorophyll content increased (33.9-86.2%) significantly at the flowering stage with ZnO and Fe₂O₃ NPs applications, compared to their conventional counterparts. Likewise, the combined application of ZnO and Fe₂O₃ NPs reduced H₂O₂ production by 17-19% and increased the superoxide dismutase (SOD) and catalase (CAT) activities by 15-17% and 9.6-11.4% over the combined use of ZnSO₄ and FeSO₄, respectively. The normalized difference vegetation index (NDVI) showed an increase of 6.9-44.2% under ZnO and Fe₂O₃ NPs, as well as ZnSO₄ and FeSO₄. Furthermore, the combined application of NPs enhanced soybean seed yield by 4.6-18.3% compared to conventional Zn and Fe fertilizers. Concerning seed Zn and Fe density, conjoint application of ZnO and Fe₂O₃ NPs increases Zn by 1.8-2.2-fold and Fe by 19.22-22.58% over the combined application of Zn SO₄ and FeSO₄, respectively. While the application of NPs significantly decreased seed phytic acid concentrations by 7.3-59.9% compared to the control. These findings suggest that the combined application of ZnO and Fe₂O₃ NPs effectively enhances soybean productivity, seed nutrient density, and overall produce quality. Therefore, the combined application of ZnO and Fe₂O₃ -NPs in soybean can be a potential approach for sustainable soybean production and to reduce/arrest Zn and Fe malnutrition in a growing population.