Cadmium bioavailability in agricultural soil after mixed amendments combined with rice-rape cropping: a five-season field experiment

Purpose Crop contamination with cadmium (Cd) poses a serious health risk in some regions of the world. A field experiment involving a cropping pattern of rice ( Oryza sativa L.) and rape ( Brassica napus L.) was conducted over five cropping seasons, with annual application of mixed amendments, to assess the feasibility of immobilizing bioavailable Cd in soil. Materials and methods From April 2016 to March 2018, a field trial with a rice-rape rotation was conducted. Mixed amendments, including lime + organic fertilizer (LO), lime + organic fertilizer + calcium-magnesium phosphate fertilizer (LOC), lime + organic fertilizer + sepiolite (LOS), and lime + organic fertilizer + calcium-magnesium phosphate fertilizer + sepiolite (LOCS), were added to the Cd-contaminated agricultural soil. Results The mixed amendments significantly reduced soil Cd bioavailability and thus notably reduced Cd concentrations in brown rice by 51.5–80.2% during the years 2016–2018 with annual application. However, soil available nitrogen contents decreased by 18.5–44.6% in the third year with the amendments applied. At the same time, the grain yields significantly decreased by 37.9–57.0% for both rape and rice, except for the continual application of LOCS. Thus, LOCS is a more optimal measure to ensure the yield and quality of rice and rape in Cd-contaminated agricultural soil when mixed amendments are continuously applied. Conclusion The mixture of organic and inorganic amendments works well for soil Cd immobilization and crop Cd reduction, while it decreases crop yields, except for LOCS. The optimal approach is to apply LOCS to Cd-contaminated soil continuously for 2 years at several-year intervals. Graphical Abstract