Iron Sulfide-Impregnated Sepiolite Nanocomposite (FeS-Sp NC) Induced Differential Responses in Physiology, Iron Modulation, Biochemical Assays, and Antioxidative Defense in Direct-Seeded Rice

Direct-seeded rice (DSR) faces low iron bioavailability due to the plurality in the oxidation states of iron. Rapid ferrous oxidation in low-irrigation soils poses a challenge to the optimum supply of iron for the initial growth in rice. Using advancements in nanotechnology, a new iron formulation, iron sulfide-impregnated sepiolite nanocomposite (FeS-Sp NC), was prepared by an in situ combination of ferrous and sulfide ions on a sepiolite matrix under ultrasonic irradiation. Nanopriming of rice seeds (PR 126) with FeS-Sp NC at an optimized dose (500 μg/g) for 12 h revealed a notable enhancement in seedling growth metrics, namely, germination percentage (15.39%), shoot length (40.54%), root length (21.67%), seedling fresh weight (15.57%), dry weight (11.36%), and vigor index (28.50%) with augmented iron content, outperforming traditionally used FeSO₄ (at an optimized dose of 750 μg/g). Enhanced activity of defensive enzymes (in shoot, root), viz. SOD (13.81%; 8.78%), APX (16.66%; 3.31%), CAT (10.84%; 13.83%), and PPO (150.41%, 191.30%) indicated a stronger defense mechanism. The elevated levels of total phenolics (49.81%; 28.79% in shoot and root respectively), flavonoids (21.75% in roots), DPPH (37.15% in roots), and ABTS (13.79% in roots) as compared to FeSO₄ further rationale the invigoration of the rice seeds. Overall, FeS-Sp NC-infused nanopriming presented superior invigoration potential over FeSO₄ mediated by an antioxidative defense mechanism due to enhanced iron assimilation in seedlings, offering a promising solution for iron modulation under sustainable agricultural practices.