Effects of Ratoon Rice Cropping Patterns on Greenhouse Gas Emissions and Yield in Double-Season Rice Regions

The ratoon rice cropping pattern is an alternative to the double-season rice cropping pattern in central China due to its comparable annual yield and relatively lower cost and labor requirements. However, the impact of the ratoon rice cropping pattern on greenhouse gas (GHG) emissions and yields in the double-season rice region requires further investigation. Here, we compared two cropping patterns, fallow-double season rice (DR) and fallow-ratoon rice (RR), by using two early-season rice varieties (ZJZ17, LY287) and two late-season rice varieties (WY103, TY390) for DR, and two ratoon rice varieties (YLY911, LY6326) for RR. The six varieties constituted four treatments, including DR1 (ZJZ17 + WY103), DR2 (LY287 + TY390), RR1 (YLY911), and RR2 (LY6326). The experimental results showed that conversion from DR to RR cropping pattern significantly altered the GHG emissions, global warming potential (GWP), and GWP per unit yield (yield-scaled GWP). Compared with DR, the RR cropping pattern significantly increased cumulative methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) emissions by 65.73%, 30.56%, and 47.13%, respectively, in the first cropping season. Conversely, in the second cropping season, the RR cropping pattern effectively reduced cumulative CH4, N2O, and CO2 emissions by 79.86%, 27.18%, and 30.31%, respectively. RR led to significantly lower annual cumulative CH4 emissions, but no significant difference in cumulative annual N2O and CO2 emissions compared with DR. In total, the RR cropping pattern reduced the annual GWP by 7.38% and the annual yield-scaled GWP by 2.48% when compared to the DR cropping pattern. Rice variety also showed certain effects on the yields and GHG emissions in different RR cropping patterns. Compared with RR1, RR2 significantly increased annual yield while decreasing annual GWP and annual yield-scaled GWP. In conclusion, the LY6326 RR cropping pattern may be a highly promising strategy to simultaneously reduce GWP and maintain high grain yield in double-season rice regions in central China.