Effect of Biochar Addition on N2O Emission from Paddy Field under Water-Saving Irrigation

Global warming is a serious problem for human beings, and biochar is proposed to potentially mitigate greenhouse gases from farmland. We conducted a field experiment to explore the effect of biochar addition on N2O emission from paddy field under water-saving irrigation. The experiment comprised three treatments: 0, 20, and 40 t ha(-1) rice-straw biochar application named CA, CB, and CC, respectively. The N2O fluxes and cumulative emissions were studied through static chamber technique. Moreover, the effects of biochar addition on rice yield and irrigation water productivity were analyzed. Results showed that N2O emissions are mainly concentrated at the early growth stage of rice and remained at a low level. Biochar addition increased the N2O emission rate in the early period (before 40 DAT, day after transplantation) compared with control, especially the N2O emission peak, whereas biochar frequently decreased the N2O emission rate in the later period (after 40 DAT). In the entire growth period, N2O average flux at a medium (20 t ha(-1)) amount of biochar addition was 2.6 times higher compared with that of control, whereas high-biochar (40 t ha(-1)) addition increased by 39.6% (231.7, 600.2 and 323.4 mu g m(-2) h(-1) for CA, CB and CC, respectively). The N2O cumulative emission from paddy field under water-saving irrigation was 462.7 mg m(-2) with high-biochar addition and decreased by 11.7% compared with control (524.0 mg m(-2)), whereas medium-biochar addition treatment (866.0 mg m(-2)) increased the emission by 65.3%. Biochar addition increased the rice yield by 9.3 and 15.8% and irrigation water productivity by 15.1 and 19.0% at the medium and high addition levels, respectively. Therefore, 40 t ha(-1) biochar addition can simultaneously mitigate N2O emissions and increase rice yield and irrigation water productivity. (C) 2018 Friends Science Publishers