https://orcid.org/0000-0003-1451-0530
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ABSTRACT
Our previous pot experiments showed that using Azolla either or both as dual and green manure with rice increases its yield or significantly reduces either or both methane (CH4) and nitrous oxide (N2O) emissions. To confirm these findings in an actual field, Azolla was either grown as a dual crop (herein Cover) or incorporated as green manure plus dual cropping (herein AGM + Cover) at the beginning of the experiment along with rice. Compared with the control (chemical fertilizer; herein NPK), NPK + Cover and AGM + Cover treatments did not influence cumulative CH4 emissions throughout the rice growth period. However, AGM + Cover treatment affected significant CH4 emissions at early, middle, and later rice growth stages by 140.6%, 24.6%, and 33.1%, respectively, compared with NPK + Cover treatment. These emissions were attributed to the readily available carbon substrate for methanogens following the incorporation of Azolla as green manure. Compared with NPK, NPK + Cover and AGM + Cover significantly increased N2O emissions by 645.9% and 816.2%, respectively, during the middle rice growth stage. No significant N2O emission differences were observed in the three treatments in the early or later rice growth stages. The higher N2O emissions from the middle rice growth stage were ascribed to high substrate availability from the dead Azolla by higher summer air temperature in the 2019 season. AGM + Cover significantly decreased rice yield by 37.5% (NPK) and 35.3% (NPK + Cover), with no significant differences between NPK and NPK + Cover. This reduction was attributed to nitrogen immobilization from the incorporated Azolla during the early stage. Therefore, to ascertain the potential of Azolla in paddy fields to address environmental safety while sustaining yield, emphasis on the interaction of different application methods with various management practices is necessary.
Acknowledgments
First, we thank all members in the Soil Science and Plant Nutrition Laboratory (Faculty of Agriculture, Yamagata University) for their assistance in field and laboratory research managements. Secondly, we thank Mrs. Kazuhiro Nagasawa and Masashi Tanno of the Yamagata Integrated Agricultural Research Center for providing us with the gas measurements chambers. We also thank members of the Institute of Agro-Environmental Sciences, NARO, Tsukuba, Japan, for their assistance with gas analysis. This work was supported by a 2019 Student Research Support Fund from The United Graduate of Agricultural Sciences, Iwate University, Japan, and partly supported by Yamagata University YU-COE(C) programs of “Yamagata University Carbon Neutral Research Center (YUCaN)” and “Food, Agriculture, and Environmental Researches for SDGs.”
Disclosure statement
No potential conflict of interest was reported by the author(s).
Supplementary material
Supplemental data for this article can be accessed here.
