[Field greenhouse gas emission characteristics and carbon footprint of ratoon rice].

It is of great significance to understand the effects of different rice cultivation methods in southeast China on greenhouse gas emission characteristics and carbon footprint of paddy fields during rice cultivation for rice sustainable production. In this study, the popular conventional rice 'Jiafuzhan' and hybrid rice 'Yongyou 2640' were used as materials to establish four rice cultivation patterns suitable for different ecological types in Fujian Province: 1) double-cropping system, early rice and late rice with Jiafuzhan (D-J); 2) early maturing ratooning system, first season rice and ratooning season rice with Jiafuzhan (R-J); 3) middle-maturing ratooning system, first season rice and ratooning season with Yongyou 2640 (R-Y); and 4) single cropping system with Yongyou 2640 (S-Y), which should be synchronized in heading time with the counterpart (the ratooning season rice). Greenhouse gas emissions from paddy soil were measured by the closed static black box observation method and the gas chromatography method, respectively. The total direct and indirect greenhouse gas emissions (carbon footprints) from different rice farming patterns were evaluated by using the life cycle analysis. The results showed that greenhouse gas emissions in different rice cropping systems were lower in the early growth stage, then decreased after reaching the peak at the booting stage, demonstrating a double peak curve in the whole growth stage, in which the first peak was higher in early season or first season than the second peak in the late season or ratooning season in the cropping patterns. Moreover, the total greenhouse gas emissions were significantly different among cropping systems. The global warming potential (GWP) of different cropping patterns was in order of R-Y>D-J>S-Y>R-J, while the annual greenhouse gas emission intensity (GHGI) was D-J>S-Y>R-Y>R-J. GWP and GHGI of the ratooning system decreased by 26.1% and 14.1%, respectively, compared with those of the double-cropping system. The same pattern was observed in the ratooning rice of Yongyou 2640, which were decreased by 74.3% and 56.7%, respectively, compared with the counterpart, Yongyou 2640 in a single-cropping system synchronized heading. Carbon footprint of rice per unit yield ranged from 0.38-1.08 kg CO-eq.·kg under the different cropping systems, of which the carbon footprint of rice per unit yield was the highest under the double cropping system compared with that under other cropping systems. The reverse was true in the case of carbon footprint of rice per unit yield under the ratooning system with Yongyou 2640. Additionally, the main source of carbon footprint of different rice cropping patterns was CH, contributing 44.2%-71.5%, suggesting that rice ratooning system could significantly reduce global warming potential and carbon emission intensity of rice in comparison with other cropping patterns. Therefore, it is key to select rice varieties with high yield and low carbon emission and to establish the supporting scientific cultivation techniques for effective reduction of CH emission and carbon footprint of paddy fields and promotion of ratooning rice production.