Iron Fertilization of Soybean Genotypes Differing in Iron Use Efficiency Under Alkaline Conditions: Implications for Yield and Seed Nutritional Quality

ABSTRACT Background Soybean, a nutritionally important protein‐ and oil‐rich legume, is highly sensitive to iron (Fe) deficiency under alkaline conditions, where reduced Fe availability limits growth, yield, and seed quality. Effective biofortification therefore requires increasing seed Fe while reducing phytate that restricts Fe bioavailability. Aims We evaluated IDC‐tolerant and sensitive soybean cultivars under graded Fe‐EDDHA supply, focusing on Fe acquisition, micronutrient interactions, and seed nutrition. Methods A greenhouse pot experiment used peat:perlite (2:1) at pH 5.7 (control) or 8.7 (alkaline). Two IDC‐tolerant (Arısoy, Sa–88) and two IDC‐sensitive (Nova, Atakişi) cultivars received a single Fe‐EDDHA application (0.75–2.60 mg Fe kg −1 substrate) under alkalinity with zero‐Fe controls. Physiological traits, ferric reductase activity, minerals, Fe‐homeostasis gene expression, and seed nutritional characteristics were assessed at defined developmental stages. Results Alkalinity reduced leaf Fe status and seed Fe concentrations, with stronger penalties in IDC‐sensitive cultivars (48% decrease vs. 15% in tolerant cultivars under Fe deficiency). Fe‐EDDHA improved chlorophyll‐related traits, leaf Fe recovery, seed Fe, protein content, and yield components more efficiently in tolerant cultivars, whereas sensitive cultivars required higher Fe doses for partial recovery. Fe deficiency increased seed phytate and phosphorus, while Fe resupply reduced phytate in most cultivars. Expression patterns of FRO/IRT1‐like , OPT3 , and FER supported genotype‐dependent differences in Fe acquisition, long‐distance signaling, and storage. Conclusions Combining genotype selection with targeted Fe fertilization improves Fe nutrition, yield‐related traits, and seed nutritional quality under alkaline conditions, supporting integrated strategies for soybean Fe biofortification.