Recalcification‐Driven Restoration of Degraded Calcareous Soil for Metal Sequestration: Insights From Soil Solution Chemistry Dynamics

Abstract

Human‐induced carbonate depletion in the tillage layer of calcareous soils transforms critical metal sinks into significant pollution sources. This study compared the efficacy of agricultural/industrial byproducts (eggshell powder, shell powder, and sugar beet factory lime [SBFL]) versus natural lime materials (calcite and dolomite) for cadmium (Cd) and lead (Pb) immobilization during the recalcification of degraded calcareous soils. Analysis of soil solution chemistry revealed that SBFL uniquely combined pH elevation across all stages (0.12–1.16 units) with elevated dissolved organic carbon (DOC) concentrations at the seedling and jointing stages (145%–472% increase) to achieve dual Cd‐Pb stabilization. Principal component analysis identified distinct immobilization mechanisms: Cd immobilization was primarily pH‐driven via precipitation and co‐precipitation with calcium, whereas Pb stabilization relied on DOC‐mediated complexation under high pH conditions, effectively suppressing the reductive dissolution of iron and manganese oxides. Consequently, SBFL outperformed the other amendments, reducing root Cd/Pb concentrations by 11.8%–56.6% and enhancing wheat biomass by 25.9%–55.4% compared with the unamended control. These findings highlight the significant potential of industrial byproducts like SBFL to restore degraded calcareous soils through distinct geochemical pathways, reconciling crop productivity with metal sequestration.