Application of iron nano-biofertilizers as a sustainable approach to enhance growth and micronutrient uptake in soybean

Iron (Fe) is an essential micronutrient for plant growth and development; however, its bioavailability in soil is often limited, resulting in reduced crop productivity. This study investigated the green synthesis of Fe nano-biofertilizers using bacteria ( Bacillus subtilis ), fungi ( Aspergillus niger ), and wheat residue extract, and evaluated their effects on soybean growth, biomass accumulation, and micronutrient uptake under greenhouse conditions. Fe nano- biofertilizer was characterized for morphology, elemental composition, functional groups, and stability, revealing that bacterial-based nanoparticles were smaller, more uniform, and contained higher Fe content, whereas fungi- and plant-based nanoparticles exhibited greater organic coating. Greenhouse experiments demonstrated that the type of biological agent, Fe salt source, and applied dose significantly influenced plant height, greenness index, fresh and dry biomass. Fungi-based nanoparticles from Fe nitrate at 30 mg kg − 1 maximized Fe uptake (737 µg pot − 1 ) in aerial parts, followed by bacterial sulfate nanoparticles at 50 mg kg − 1 (621 µg pot − 1 ) and wheat chloride nanoparticles at 30 mg kg − 1 (570 µg pot − 1 ). Fe nano-biofertilizer generally enhanced Cu, Zn, Mn, and Fe accumulation compared to wheat-based nanoparticles and chemical fertilizers, reflecting improved nutrient availability and translocation. Response Surface Methodology (RSM) revealed significant linear, quadratic, and interaction effects among biological agent, Fe source, and dose, highlighting the nonlinear nature of plant responses. Also, among sources of Fe sulfate, it showed higher efficiency than other sources. These findings provide a sustainable and eco-friendly strategy for improving Fe nutrition in crops, demonstrating the potential of Fe nano bio-fertilizer to enhance crop productivity, nutrient use efficiency, and environmental safety in modern agriculture.