Converter-slag lime enhances the reduction of radiocesium transfer from andosol-based reconstructed soil after decontamination to soybean under high exchangeable potassium condition

Following the 2011 Fukushima Daiichi nuclear accident, considerable efforts have been made to reduce the transfer of radiocesium (137Cs) from soil to crops in the affected areas. Potassium fertilization suppresses 137Cs uptake; however, the effectiveness of other soil amendments remains poorly understood. This study compared two lime materials – magnesium lime (ML; 550 g kg−1 CaO and 150 g kg−1 MgO) and converter-slag lime (CL; 470 g kg−1 CaO, 38 g kg−1 MgO, 143 g kg−1 SiO2, 281 g kg−1 Fe2O3, and trace micronutrients) – for their influence on 137Cs transfer from Andosol to soybean (Glycine max L.). Field trials were conducted over two years, with both materials applied at the same CaO rate (110 g m− 2). In parallel, a glasshouse pot experiment used the same soil with four CaO levels (0, 2.8, 5.6, and 8.4 g pot−1). Transfer factors (TF = 137Cs in plant / total 137Cs in soil) and exchangeable transfer factors (Ex-TF = 137Cs in plant / exchangeable 137Cs in soil) were calculated for shoots (pot experiment) and grains (field experiment). In the pot study, both liming materials reduced shoot TF relative to the untreated control. Analyses of plant nutrition and soil chemical properties suggest that mitigation of 137Cs transfer by lime amendments involves two synergistic mechanisms: (1) growth promotion that dilutes 137Cs concentrations in plant biomass and (2) increased soil pH that reduces Cs ion solubility. Across both pot and field experiments, CL was more effective than conventional ML in mitigating 137Cs transfer to soybean in potassium-rich Andosol. The greater reduction with CL suggests multiple contributing mechanisms, including (1) competition between Ca and Cs ions during root uptake under high-potassium conditions and (2) enhanced adsorption of Cs ions onto components accompanying CL. The application of CL exerts an additive inhibitory effect on 137Cs transfer under high exchangeable K conditions, offering a more potent and sustainable remediation strategy that simultaneously enhances the value of industrial slag waste.