Enhancing Wheat Grain Safety via Chelated Iron Fertilizer–Induced Iron Turnover and Cadmium Immobilization in Alkaline Soils

Cadmium (Cd) contamination in alkaline soils threatens wheat grain safety and iron (Fe) nutrition, yet conventional remediation strategies often show limited effectiveness in soils with circumneutral or alkaline pH. Here, multiyear pot and field experiments showed that Fe(III)-EDTA, a chelated Fe fertilizer, reduced wheat grain Cd accumulation across soil and cultivar systems while increasing grain Fe concentration. At 120 mg kg –1 Fe(III)-EDTA, DTPA-extractable Cd and grain Cd decreased by 46.5–67.1% and 25.9–70.5%, respectively, in pot trials, while grain Fe increased by 59.2–94.6%. Field application reduced soil DTPA-extractable Cd and grain Cd by 48.2% and 28.9%, respectively, and a single application sustained Cd suppression across subsequent growing seasons. Mechanistic experiments supported a biphasic Cd trajectory in which Fe(III)-EDTA first mobilized reactive Fe and Cd pools through ligand-driven processes, whereas rhizosphere-relevant conditions promoted subsequent Fe transformation, phase reorganization, and Cd redistribution into less extractable Fe-associated pools. This mechanism distinguished Fe(III)-EDTA from EDTA-Na, which mobilized Cd without Fe-mediated recapture, and from FeSO 4, which supplied Fe without efficiently activating reactive Fe/Cd pools. Mineralogical and microscale evidence supported Fe phase restructuring and Cd relocation toward Fe-rich domains. These findings broaden the role of chelated Fe fertilizers from nutrient supplementation to process-based regulation of metal fate in contaminated alkaline soils.