A field study of biochar application impact on adsorption and accumulation of Cd in paddy soil and rice

Biochar application to soil contaminated with potentially toxic elements has been paid particular attention as an effective amendment. This study was carried out to investigate the effect of wheat straw biochar on adsorption and accumulation of Cd2+ in paddy soil and rice. Biochar was applied once in four treatments of 10, 20, 30, and 40 t ha−1 and a control check (CK) was set up in Changsha County, China. The results showed that under biochar addition the Cd2+ adsorption process was dominated by inhomogeneous multi-surface adsorption. Biochar significantly increased adsorption capacity for Cd2+ and the maximum of sorption at A40 was 2713 mg kg−1. The available Cd concentration was also decreased by transforming S1 (decreased by 25%, acid soluble Cd) to S2 (increased by 40%, oxidizable Cd) and S3 (increased by 24%, reducible Cd). Also, biochar application resulted in significant reduction in Cd concentration in rice by inhibiting migration from soil to rice. The study demonstrated that the biochar of 40 t ha−1 reduced rice grain Cd concentration to 0.18 mg kg−1, which was within the Chinese safety limit. Therefore, the dose of 40 t ha−1 would be proper for reducing risk due to Cd contamination in agricultural production.