Biochar soil amendment as a solution to prevent Cd-tainted rice from China: Results from a cross-site field experiment

Cadmium contamination in croplands has been a serious concern because of its high health risk through soil-food chain transfer. A sudden emergence of Cd-tainted rice from the South China market urged countermeasures to prevent Cd uptake and accumulation in rice grains from Cd-contaminated rice paddies. A cross-site field experiment with biochar soil amendment (BSA) at rates from 20 to 40 t ha−1 in metal polluted rice fields was conducted across South China during 2010-2011. Samples both of topsoil and rice grains under BSA treatment were collected after rice harvest and soil extractable Cd pool and rice grain Cd level were analyzed. Across the sites, BSA treatment greatly reduced (by 20-90%) rice grain Cd content, and enabled a safe Cd level (<0.4 mg kg−1) of rice grain from all these Cd-contaminated rice fields using a 40 t ha−1 biochar application except in one site where soil had a Cd content over 20 mg kg−1. This could be explained by a reduction in the extractable Cd pool in the biochar treated soil, which was closely correlated to the rise in soil pH with BSA treatment. This study demonstrated a promising role of BSA in preventing dangerous Cd accumulation by rice grain in contaminated rice paddies.