Abstract: Biochar returning may be an important way to deal with climate change for mankind. To investigate the effects of different biochar types, returning amount, returning time and returning depth on CH4 emission, a greenhouse experiment of CH4 emissions with three different biochar, namely rice carbon (RC), wheat carbon (WC), bamboo carbon (BC) applied on the paddy field and no biochar application as a control (CK), was conducted by using the static chamber-GC (gas chromatography) method during the rice growing season (2011-2012). The results showed that the yield was significantly increased (P<0.05) after different biochar returning compared with the control treatment(CK), and the highest filled grain weight of BC treatment reached 18.12 g per pot, which showed biochar returning can effectively increase rice yield. The CH4 emission flux of BC treatment was significantly higher (P<0.05) than that of WC and RC treatments, and for the later two treatments, there were no significant differences (P>0.05), but they were significant higher (P<0.05) than that of CK, which showed biochar returning can decrease CH4 emission efficiently. A linear negative correlation was found between CH4 emission flux and biochar application amount, and CH4 emission flux declined gradually with the increase of the cycle of biochar returning amount. Meanwhile, the CH4 emission flux of bamboo carbon (BC) returning before rice transplantation (BRT, 56.6 mg·m-2·h-1) was not significant lower (P>0.05) than those of CK (96 mg·m-2·h-1) and before rice survival (BRS,73.4 mg·m-2·h-1) or after rice survival(ARS, 76.6 mg·m-2·h-1), which was consistent to the change of soil redox potential (Eh) and showed biochar returning time has little effect on CH4 emission flux. In addition, the sequence of CH4 emission flux in different biochar returning depth was on the order of middle returning(MR)
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