Effects Of Biochar Application On Cadmium Accumulation Of Rice In Heavy Meatal Contaminated Soil

With the industrial development and widespread application of agricultural chemicals,heavy metal soil contamination,especially cadmium(Cd)contamination,has become a global concern and attracted extensive attention.Cadmium,a kind of trace metal with the strongest biotoxicity,due to its high chemical activity and persistent toxicity in soil,poses a great potential chance to cause hazards to human health via food chains.Rice is the world’s second largest,Chinese biggest food crop,and also is one of the most easily uptake and accumulation of Cd in staple food crops.In South China,the rice production areas of heavy metal contaminated become serious with most of the acid soil,which is posing potential public health risk for human and food safety.Biochar refers to a kind of stable biomass obtained from the solid material such as corn straw by thermal cracking of hypoxic or anoxic conditions.There are such characteristics:high specific area,cation exchange capacity(CEC)and rich oxygen containing functional groups.What is more,the biochar could increase the soil pH to hold the soil nutrition elements and heavy metals because of the large surface area and surface negative electric charge.There are broad application prospects in control and remediation of soil cadmium contamination.In order to evaluate the potential of biochar and lime application in China’s croplands,a field experiment with biochar soil amendment was conducted across South China and analyze the effect of biochar on soil Cd immobilization and rice grain Cd accumulation.We also analyze the influence of biochar on rice varieties grain Cd absorption and its influence on soil physical and chemical properties.Simulating different levels of Cd,Zn pollution and biochar addition,rice pot experiments were carried out;the interaction between Cd,Zn were analyzed and the influence of Cd,Zn absorption by the application of biochar.The main results were as follows:(1)The rice husk biochar and Lime significantly improve soil pH and CEC;the pH respectively increase 0.16,0.33,the CEC respectively increase3.09,3.72cmol kg-1 in the first year;the pH respectively increase 0.17,0.10,the CEC respectively increase5.05,2.2cmol kg-1 in the next year.The both biochar can improve the SOC of soil,the lime treatment didn’t.(2)The rice husk biochar and Lime significantly reduced the soil CaCl2 extractable Cd.Compared with the control,the soil CaCl2 extractable Cd decreased respectively 54.2%,62.5%in the first year;the soil CaCl2 extractable Cd decreased respectively 48.1%,22.2%in the next year.Biochar soil amendment improve the rice yield over two years,while the Lime treatment didn’t.The rice husk biochar and Lime reduced the rice grain Cd,the Cd concentrations of rice grains are 0.22,0.28mg kg-lin the first year,which was under the limit value(0.4 mg kg-1)proposed by CCFAC;the Cd concentrations of rice grains are0.17,0.43 mg kg-1(CK =0.45 mg kg-1).This shows that lime treatment has lost the effect of reducing the rice Cd absorption in the second year.(3)Soil organic carbon and pH were significantly increased across all biochar treatments and the increase rates were 9%-15.5%and 35.5%-46.6%.The increase rates increased with the increase of applying biochar content increases.Biochar soil amendment significantly improved the conventional rice production,while didn’t improve the hybrid rice production.(4)Biochar soil amendment significantly decreased soil CaCl2 extractable Cd.Compared with the control,the soil CaCl2 extractable Cd decreased 60.6%at 20 t ha-1 biochar application,the soil CaCl2 extractable Cd decreased 84.9%at 40 t ha-1 biochar application.Biochar soil amendment induced increasing of soil pH and SOC could accout for the reduction of soil CaCl2 extractable Cd.Biochar soil amendment decreased rice grain Cd content and the reduction rates are 60%,54%.There is different absorption effect of varieties of rice on reducing cadmium,it has a lot to do with the mechanism of rice(5)Biochar soil amendment improve the rice height、grain yield、total biomass and the soil pH.The soil Cd、Zn available contents increased with the increase of Cd、Zn addition.Biochar treatment can decrease the Cd、Zn available contents in soil and rice grain Cd content,while Zn contents in grain were not increased completely by increasing Zn available contents in soil.