Azolla incorporation and dual cropping influences CH
            <sub>4</sub>
            and N
            <sub>2</sub>
            O emissions from flooded paddy ecosystems

Samuel Munyaka Kimani, Putu Oki Bimantara, Satoshi Hattori, Keitaro Tawaraya, Shigeto Sudo, Weiguo Cheng

doi:10.6084/m9.figshare.11493507.v1

To investigate the influence of Azolla (A. filiculoides Lam.) incorporated as a green manure and its subsequent growth as a dual crop with rice on simultaneous methane (CH₄) and nitrous oxide (N₂O) emissions from a flooded alluvial soil planted with rice, a pot experiment with three treatments, chemical fertilizers (NPK) as the control, incorporation of Azolla as green manure (AGM), and AGM plus basal chemical fertilizers (NPK+AGM) was conducted in Tsuruoka, Yamagata, Japan in 2017. AGM and NPK+AGM treatments significantly increased CH₄ emissions at early rice growth stages before 63 days after transplanting (DAT) by 123.0% and 176.7% compared to NPK, respectively. At late rice growth stages (after 63 DAT), only the NPK+AGM treatment significantly increased CH₄ emission by 22.1% compared to NPK. However, percentage of CH₄ emitted after 63 DAT relative to the seasonal CH₄ emission followed the order of NPK (86.2%) > AGM (76.5%) > NPK+AGM (73.3%). Higher CH₄ emissions from AGM and NPK+AGM before 63 DAT were attributed to the incorporated Azolla, while the higher emissions after 63 DAT in all treatment groups were ascribed to rice photosynthesis. AGM and NPK+AGM treatments significantly decreased N₂O emissions by 71.6% and 81.1% compared to NPK, respectively, at early rice growth stages. Azolla incorporation may have restricted N₂O emission from initial soil nitrate before 63 DAT and not have contributed to N₂O emissions after 63 DAT. Significantly higher grain yields were observed under the AGM (32.5%) and NPK+AGM (36.3%) compared to NPK. Together, AGM and NPK+AGM treatments significantly increased seasonal CH₄ emissions by 31.5% and 43.5%, and decreased seasonal N₂O emissions 3.4- and 4.6- fold compared to NPK, respectively. There were no significant differences in the CH₄ emissions per grain yield among the treatments; however compared to NPK, AGM and NPK+AGM treatments significantly reduced N₂O emissions per grain yield by 78.7% and 84.1%, respectively.

Azolla incorporation and dual cropping influences CH <sub>4</sub> and N <sub>2</sub> O emissions from flooded paddy ecosystems

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