Mitigating effects of ex situ application of rice straw on CH4 and N2O emissions from paddy-upland coexisting system

Abstract

The in situ application of rice straw enhances CH₄ emissions by a large margin. The ex situ application of rice straw in uplands, however, may mitigate total global warming potential (GWP) of CH₄ and N₂O emissions from paddy-upland coexisting systems. To evaluate the efficiency of this practice, two field trials were conducted in rice-rice-fallow and maize-rape cropping systems, respectively. Year-round measurements of CH₄ and N₂O emissions were conducted to evaluate the system-scaled GWP. The results showed that CH₄ accounted for more than 98% of GWP in paddy. Straw removal from paddy decreased 44.7% (302.1 kg ha^-1 yr^-1) of CH₄ emissions and 51.2% (0.31 kg ha^-1 yr^-1) of N₂O emissions, thus decreased 44.8% (7693 kg CO₂-eqv ha^-1 yr^-1) of annual GWP. N₂O accounted for almost 100% of GWP in upland. Straw application in upland had insignificant effects on CH₄ and N₂O emissions, which increased GWP only by 91 kg CO₂-eqv ha^-1 yr^-1. So, the transfer of straw from paddy to upland could decrease GWP by 7602 kg CO₂-eqv ha^-1 yr^-1. Moreover, straw retention during late rice season contributed to 88.2% of annual GWP increment. It is recommended to transfer early rice straw to upland considering GWP mitigation, nutrient recycling and labor cost.