2020 Volume 10 Pages 67-78
Methane (CH4) and nitrous oxide (N2O) are greenhouse gases; further, paddy fields are one of the anthropogenic sources of CH4. In particular, “Fuyumizu-tambo,” an early ﬂooded organic paddy ﬁeld, is known to be the primary source of CH4. Thus, we observed CH4 and N2O emissions using the chamber method in the “Fuyumizu-tambo” customary paddy ﬁelds from 2013 to 2014 at Bibai City, Hokkaido, Japan. Thus, a relation could be observed between the soil’s degree of dryness during mid-summer drainage, which is a CH4 release-inhibiting period; furthermore, CH4 was observed to be slightly released until the soil became completely dry. Because of the water retentivity of the “torotoro layer,” a type of soil containing abundant organic matter content owing to the stirring action of worm ﬁsh, drying is difﬁcult, which results in the formation of an oxidation-reduction border domain. Therefore, the release of CH4 is easy owing to the “torotoro layer.” In addition, although the abundant nitrogen content of the “torotoro layer” inhibited CH4 emission, N2O emission is not correlated to the total nitrogen (TN) concentration of the “torotoro layer,” and hence, nitrogen content directly does not cause N2O production. Therefore, controlling the water retentivity and TN concentration of the “torotoro layer” could suppress CH4 and N2O emissions from the paddy ﬁelds.