Effect of organic matter addition on cadmium solubility in alkaline paddy soils

AbstractStraw incorporation into the soil is a common agricultural practice, but its effect on soil cadmium (Cd) mobility is not well understood. We added 0–20 g kg− 1organic matters (OMs) with different C/N ratios to three spiked alkaline paddy soils that contained a realistically low concentration of total Cd (0.94 mg kg− 1), and then investigated soil Cd solubility in alternate watering conditions. Multiple soil properties were measured to identify key factors regulating dissolved Cd concentration. We found that for all three soils, pH and dissolved Cd concentration both decreased after flooding and increased after subsequent drying. OM addition significantly reduced soil Cd solubility at both flooding and drying stages. Random forest and linear regressions further confirmed that soil total organic carbon, rather than pH, dissolved organic carbon, or total inorganic carbon as previously suggested, was the primary predictor of Cd solubility. OMs with different C/N ratios had similar effects on soil Cd solubility, whereas the effect of OM addition rate depended on soils. The results demonstrated the potential of straw incorporation for the remediation of Cd-contaminated alkaline paddy soils, through mechanisms that differ from those reported in acid soils.