Sustained grain cadmium reduction in rice-wheat rotation: A cost-effective CaCO₃-based amendment strategy from...

Cadmium (Cd) contamination of agricultural soils poses a serious threat to global food safety, especially in intensive rice-wheat rotation systems where both staple grains frequently exceed regulatory limits. While soil amendments are advocated for Cd immobilization, their long-term efficacy and economic sustainability in multi-season rotations are poorly documented. In this study, we performed a continuous three-year field trial in a Cd-contaminated rice-wheat system within China's Yangtze River basin, evaluating 15 amendment strategies. These comprised agricultural limestone (CaCO₃), two newly formulated CaCO₃-based composites - FF (CaCO₃+ ZnSO₄+ MnSO₄) and FO (CaCO₃+ ZnSO₄+ MnSO₄+ organic fertilizer) - and 12 commercial products. A single pre-planting application of FO sustainably raised soil pH by 0.74-1.35 units, suppressed CaCl₂-extractable soil Cd more effectively than other treatments, and reduced grain Cd concentrations by 70-84% in rice and 38-63% in wheat across all three years, without affecting crop yield. Although pure CaCO₃, emerged as the most cost-effective option per unit Cd reduction, it did not consistently maintain wheat grain Cd below national safety threshold. Economic analysis revealed that FO was the sole amendment to generate a positive net profit over the trial period, attributable to its reliable compliance with safety standards for both crops. Our findings demonstrate that while CaCO₃ alone offers an efficient and economical Cd-mitigation measure, a purpose-designed composite such as FO delivers superior long-term stability and farm-level profitability. This work provides a practical, scalable soil-management strategy to safeguard grain production in Cd-affected rice-wheat regions.