Impacts of biochar-based amendment on soil cadmium immobilization, rice grain cadmium accumulation and yield

Abstract

Cadmium (Cd) contamination in soil is of severe health and environmental concern because of its threat to human health, food safety, and ecosystem sustainability. The in situ stabilization of Cd has been recognized as a potentially economical technique for the rehabilitation of soil polluted with Cd. Biochar has recently received much attention as an eco-friendly and recyclable soil amendment, which is more beneficial for plant growth, soil health, and restoration of contaminated soil. An experiment was performed in the field to study the efficiency of three different types of biochar: maize straw biochar, bamboo biochar, and coconut shell activated carbon in combination with rape organic fertilizer (ROF), calcium magnesium phosphate fertilizer (CMPF), and fulvic acid (MFA), respectively, on soil Cd immobilization, Cd uptake by rice, and rice yield. The experiment indicated that the biochar-based amendments reduced soil Cd bioavailability and rice Cd content by 9.58%-27.06% and 19.30%-71.77%, respectively. The transformation of exchangeable Cd (Ex-Cd) to carbonate bound Cd (Ca-Cd), Fe-Mn oxide bond (Ox-Cd), and residual (Re-Cd) in soil accounted for the mitigation of Cd absorption and enrichment by rice. In addition, the biochar-based amendments altered soil physicochemical properties and promoted soil health. Biochar-based amendments enhanced Fe and Mn plaques by 47.31%-160.34% and 25.72%-73.09%, respectively. The correlation analysis revealed that leaf Cd and Fe/Mn plaques primarily controlled Cd uptake by rice, and soil pH, Eh, CEC, SOC, Fe/Mn plaques, and TP influenced Cd bioavailability in soil. This field study demonstrated that maize straw and bamboo biochar-based amendments had a higher benefit and were potentially applicable to ameliorating metal-contaminated agricultural soil.