Biochar amendment greatly reduces rice Cd uptake in a contaminated paddy soil: A two-year field experiment

A field experiment was conducted on the effect of biochar (BC) amendment on Cd uptake by rice (Oryza sativa L.) in a contaminated paddy in 2009 and 2010. BC was applied as a basal soil amendment before rice transplantation in 2009 at rates of 0, 10, 20, 40t ha-1, and rice yield and Cd uptake were monitored in both 2009 and 2010. The BC amendment significantly increased soil pH by 0.15-0.33 units in 2009 and 0.24-0.38 units in 2010, and decreased CaCl2 extracted Cd in soil by 32.0%-52.5% in 2009 and 5.5%-43.4% in 2010, respectively. Under BC amendment at 10, 20, 40 t ha-1, rice grain Cd concentration was observed to be reduced by 16.8%, 37.1%, and 45.0% in 2009 and by 42.7%, 39.9%, and 61.9% in 2010, while the total plant Cd uptake was found to decrease by 28.1%, 45.7%, and 54.2% in 2009 and by 14.4%, 35.9%, and 45.9% in 2010, respectively. Such effect of BC amendment on reducing Cd plant uptake has profound implications among those using bioresources for field application. Finally, BC amendment in combination with low Cd cultivars may offer a basic option to reduce Cd levels in rice as well as to reduce greenhouse gas emissions in rice agriculture in contaminated paddies.