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A field trial was performed to investigate the effect of municipal biowaste biochar (MBB) on rice and wheat growth, metal bioaccumulation, and greenhouse gas emissions in a rice paddy in eastern China. MBB was amended in 2010 before rice transplanting at rates of 0 and 40 t ha-1 in a field experiment lasting one cropping year. MBB soil amendment significantly increased soil pH, total soil organic carbon, and total nitrogen. The growth and grain yield of rice and wheat was not affected with MBB application at 40 t ha-1. MBB amendment did not influence the soil availability of Pb, Cu, and Ni, but significantly increased the soil availability of Zn and decreased the soil availability of Cd during both rice and wheat seasons. While MBB did not change the bioaccumulation of Pb, Cu, and Ni, the rice and wheat Cd accumulation was significantly reduced, and wheat Zn accumulation slightly increased with MBB amendment. Furthermore, total N2O emission during both rice and wheat seasons was greatly decreased, though total seasonal CH4 emission was significantly increased in the rice season. On the other hand, soil CO2 emission remained unaffected across crop seasons. Thus, MBB can be used in rice paddy for low carbon and low-Cd grain production, but the long-term effects remain unknown.