Mitigating methane emissions and carbon footprint in rice-wheat rotation system by straw centralized returning under rainfed conditions

Direct incorporation of straw into the flooded paddy has been widely confirmed to induce substantial methane (CH4) emissions. Exploring innovative modes of straw return and associated field water management is necessary to mitigate CH4 emissions without compromising crop yield. Here, a 2-year field experiment was conducted with two wheat straw returning modes [straw evenly-plowed returning (SR) with conventional flooding water management, and straw centralized returning (SCR) under rainfed conditions], to evaluate greenhouse gas (GHG) emissions, crop yields, carbon footprint (CF), and net ecosystem economic benefit (NEEB) in the ricewheat rotation system. The results showed that the GHG emissions contributed significantly to the total annual carbon source value, accounting for 48.0 % and 43.0 % in SR and SCR, respectively. The mean CF in SCR was 6760 kg CO2-eq ha-1, which was 17.6 % lower than that in SR, primarily due to the significantly lower CH4 (by 27.5 %) during the rice seasons. Lower soil water contents might partly regulate the CH4 emissions by decreasing DOC contents and increasing the soil Eh, leading to a lower CH4 production potential (decreased by 44.3-45.8 %) and production/oxidation potential ratio in SCR. Annually, the total yields of rice and wheat were 9.53 t ha-1 and 9.38 t ha-1 in SR and SCR, respectively. However, the irrigation electricity consumption and CF costs were lower in SCR, resulting in an increased NEEB of 179 CNY ha-1 relative to SR. The findings suggest that straw centralized returning under rainfed conditions in the rice season could reduce both CH4 emissions and carbon footprint while sustaining food security and economic benefit in the rice-wheat rotation system.