Mitigating effects of ex situ application of rice straw on CH 4 and N 2 O emissions from paddy-upland coexisting system

The in situ application of rice straw enhances CH 4 emissions by a large margin. The ex situ application of rice straw in uplands, however, may mitigate total global warming potential (GWP) of CH 4 and N 2 O 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 CH 4 and N 2 O emissions were conducted to evaluate the system-scaled GWP. The results showed that CH 4 accounted for more than 98% of GWP in paddy. Straw removal from paddy decreased 44.7% (302.1 kg ha −1 yr −1 ) of CH 4 emissions and 51.2% (0.31 kg ha −1 yr −1 ) of N 2 O emissions, thus decreased 44.8% (7693 kg CO 2 -eqv ha −1 yr −1 ) of annual GWP. N 2 O accounted for almost 100% of GWP in upland. Straw application in upland had insignificant effects on CH 4 and N 2 O emissions, which increased GWP only by 91 kg CO 2 -eqv ha −1 yr −1 . So, the transfer of straw from paddy to upland could decrease GWP by 7602 kg CO 2 -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.