Abstract
<title>Abstract</title> <p>Soybean productivity in saline environments is severely constrained by salt-induced physiological and biochemical disturbances. A pot experiment was conducted from November 2023 to February 2024 at the Department of Agronomy, Gazipur Agricultural University, Bangladesh, to evaluate the effects of foliar-applied Fe₃O₄ nanoparticles (NPs) on soybean under salinity stress. The experiment followed a completely randomized factorial design with two salinity levels (0 and 75 mM NaCl) and six Fe₃O₄ NP concentrations (0-500 ppm). Salinity stress significantly reduced growth, physiological performance, chlorophyll content, and yield-related traits, while increasing stress-associated parameters including malondialdehyde (MDA), proline, hydrogen peroxide (H₂O₂), and water saturation deficit. Foliar application of Fe₃O₄ NPs was associated with partial alleviation of salinity-induced reductions in several measured traits. Among the tested concentrations, 400 ppm generally showed comparatively better performance in terms of biomass accumulation, relative water content, chlorophyll content, membrane stability index, and yield-related parameters under saline conditions. Exploratory correlation and principal component analyses indicated positive associations among yield and several physiological traits, whereas stress-associated traits showed negative relationships with yield performance. The findings suggest that moderate concentrations of Fe₃O₄ NPs may improve soybean performance under salinity stress conditions. However, because soluble iron controls and independent nanoparticle characterization were not included, nanoparticle-specific effects could not be conclusively established.</p>