Sulfide-Infused FeS-Palygorskite Nanohybrid with Redox-Modulating Properties Improves Iron Assimilation and Physiological-Biochemical Performance in Soybean

Iron (Fe) deficiency in alkaline soils severely constrains crop productivity, threatening global food security and resilience. This study reports the synthesis of an iron sulfide-palygorskite nanohybrid (FeS-S^2-@Pal) infused with equimolar sulfide ions to create a reducing environment that enhances Fe²⁺ stability and uptake in soybean. Structural characterization confirmed stability, while controlled-release kinetics (<i>k</i>_h = 0.036) indicated prolonged Fe²⁺ retention compared to FeS@Pal (<i>k</i>_h = 0.049). Pot experiments in alkaline soil (3.15 mg kg^-1) showed improvements in germination (12.9%), dry biomass (16.6%), vigor (31.6%), and Fe assimilation (shoots 30%, roots 60%), along with higher chlorophyll (23.2%) and carotenoids (30.0%). Enhanced antioxidant enzymes (SOD, CAT, APX, POD, PPO) and nonenzymatic antioxidants (phenolics, flavonoids, proteins, DPPH, ABTS) indicated effective oxidative stress mitigation. Sulfide incorporation stabilized Fe²⁺, promoting efficient nutrient assimilation and physiological performance. Thus, FeS-S^2-@Pal represents a sustainable, redox-active nanofertilizer that supports the energy-food-water nexus and strengthens agricultural resilience under environmental stress.