The comparison of biochar-based amendments in reducing both Cd and As absorption and transfer by spring and autumn rice

It is considered as a major and urgent problem in this region for safe utilization of the paddy soil contaminated by both Cd and As. This study compared the effects of 4 carbon-based amendments on the absorption, enrichment and transport of Cd and As in early and late rice plants through field experiments, in order to screen out suitable amendments for safe utilization of polluted farmland and provide scientific basis for the safe utilization of polluted soil. Both Oryza sativa L.Ruanhua You 6100 (spring rice) and Oryza sativa L. Ye Xiang You 9 (autumn rice) commonly used in Guangdong Province were used as test rice plants. Four different biochar-based amendments were invloved such as CK, BO (biochar: organic fertilizer=1∶1), BS (biochar: sepiolite=1∶1), BB (biochar: bentonite=1:1), and BA (biochar: alkali residue=1:1). The measured parameters were included the grain yield, the contents of both Cd and As in the major organs in rice plant. The biological accumulation factor (BCF) and transfer factor (TF) were calculated. The results showed that biochar-based amendments could significantly increase the grain yield of both spring rice by 26.87%−48.93%, while BO treatment significantly increased the yield of autumn rice by 26.16%. Biochar-based amendments induced large reduction in Cd content of both brown spring and autumn rice by 40.23%−67.89% and 7.64%−32.91% respectively. However, the amendments increased the As content in spring rice by 44.09%−67.73%, while with little effect on autumn rice. Generally, BS had consistent performance in spring and autumn rice for the best reduction in Cd but increase in As. Soil available Cd was significantly and negatively correlated with soil pH and CEC, while soil available As was not significantly correlated with soil physicochemical properties. The Cd content in brown rice was significantly and positively correlated with soil available Cd, and the Cd contents in brown rice, rice straw and rice root. There were significant negative correlations among As content in brown rice and the Zn content in brown rice, rice husk and rice straw as well. It is evident for that different methods based on the absorption and transport mechanisms of different heavy metals must be implemented for controlling both Cd and As content in rice. Our results provide a theoretical basis for controlling the Cd and As content in rice in southern China.