Methane and nitrous oxide emissions from a ratoon paddy field in Sichuan Province, China

Ratoon rice (RR) is a practice that involves achieving a second crop originating from the stubble left after the previous main rice crop (MR) harvest. There has been little previous study on methane (CH4) and nitrous oxide (N2O) emissions from ratoon paddy fields. A 3-year field experiment was conducted to simultaneously measure CH4 and N2O emissions from traditional single rice (SR) and MR + RR fields in Sichuan Province, southwest China. The CH4 and N2O flux peaks were earlier for MR than SR. The CH4 emissions from the RR season accounted for 8-30% of total emissions from MR + RR. Compared with SR, MR + RR increased seasonal CH4 emissions by 3-15%. Correlation analysis showed that the seasonal variation of CH4 fluxes for MR + RR was significantly related to soil redox potential (Eh). The proportion of emitted N2O from RR to MR + RR was 11-42%. The average cumulative N2O emissions from MR and MR + RR were increased by 49 and 110% relative to those from SR plots across the 3 years, respectively. The global warming potential (GWP) of RR occupied 10-27% of MR + RR. The GWP of MR + RR was 7-62% higher than that of SR, and it was chiefly dependent on the contribution of CH4 emissions, despite the greater increase in N2O emissions. Grain yield in RR was 11-18% of that in MR + RR. MR + RR significantly increased rice yield by 19%, but the yield-scaled GWP was comparable to SR. Our results suggest that MR + RR increases the amount of CH4 and N2O emissions from rice paddy fields and rice grain yield. The yield gaps of ratoon rice would be narrowed by optimizing field management practices to realize sustainable rice production under future climate change conditions. The CH4 and N2O emission peaks of ratoon rice were earlier than those of single rice. The CH4 and N2O emissions from ratoon rice fields were significantly higher than from single rice fields. Ratoon rice significantly increased yield and GWP compared to single rice. No significant difference in yield-scaled GWP was observed between ratoon rice and single rice. Highlights The CH2 and N2O emission peaks of ratoon rice were earlier than those of single rice. The CH4 and N2O emissions from ratoon rice fields were significantly higher than from single rice fields. Ratoon rice significantly increased yield and GWP compared to single rice. No significant difference in yield-scaled GWP was observed between ratoon rice and single rice.