Mitigating effects of ex situ application of rice straw on CH and NO emissions from paddy-upland coexisting system.

The in situ application of rice straw enhances CH emissions by a large margin. The ex situ application of rice straw in uplands, however, may mitigate total global warming potential (GWP) of CH and NO 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 and NO emissions were conducted to evaluate the system-scaled GWP. The results showed that CH accounted for more than 98% of GWP in paddy. Straw removal from paddy decreased 44.7% (302.1 kg ha yr) of CH emissions and 51.2% (0.31 kg ha yr) of NO emissions, thus decreased 44.8% (7693 kg CO-eqv ha yr) of annual GWP. NO accounted for almost 100% of GWP in upland. Straw application in upland had insignificant effects on CH and NO emissions, which increased GWP only by 91 kg CO-eqv ha yr. So, the transfer of straw from paddy to upland could decrease GWP by 7602 kg CO-eqv ha yr. 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.