Impacts of rice varieties and management on yield-scaled greenhouse gas emissions from rice fields in China: A meta-analysis

Increasing numbers of studies have suggested that a comprehensive assessment of the impacts of cropping practices on greenhouse gas (GHG) emissions per unit yield (yield-scaled), rather than by land area (area-scaled), is needed to inform trade-off decisions to increase yields and reduce GHG emissions. We conducted a meta-analysis to quantify impacts of rice varieties on the global warming potential (GWP) of GHG emissions at the yield scale in China. Our results showed that significantly higher yield-scaled GWP occurred with indica rice varieties (1101.72 kg CO2 equiv.Mg-1) than japonica rice varieties (711.38 kg CO2 equiv.Mg-1). Lower yield-scaled GHG emissions occurred within 120-130 days of growth duration after transplanting (GDAT; 613.66 kg CO2 equiv.Mg-1), followed by 90-100 days of GDAT (749.72 kg CO2 equiv.Mg-1), 100-110 days of GDAT (794.29 kg CO2 equiv.Mg-1), and 70-80 days of GDAT (800.85 kg CO2 equiv.Mg-1). The fertilizer rate of 150-200 kg N ha(-1) resulted in the lowest yield-scaled GWP. Consequently, appropriate cultivar choice and pairs were of vital importance in the rice cropping system. A further life cycle assessment of GHG emissions among rice varieties at the yield scale is urgently needed to develop win-win policies for rice production to achieve higher yield with lower emissions.