A study on characteristics of Methane emission from a periodically irrigated paddy field in Japan

Abstract:

Methane (CH₄) is generated by organic matter decomposition in the anaerobic soil. Paddy field is one of the most important eco-system in monsoon Asia. It is said that about 10% of CH₄sources is paddy fields (IPCC AR4, 2007). In this study, methane emission from a single-rice crop field was estimated by long-term micrometeorological measurements. Methane emission was calculated by the aerodynamic gradient technique from January 2011 to August 2014. Intermittent water management was carried out during cultivation period at the observational site, HCH, located in Okayama, Japan. 3-days flood and 4-days drained condition were regularly repeated from late-June to early October.

Seasonal variations of CH₄flux for irrigation term from 2011 to 2013 were shown in Fig.1.

Remarkably large fluxes were shown at early stage of irrigation term in 2011.It seemed to be caused by the relatively longer flooded condition that the first flooded period was 20 days.

Flux in 2012 was smaller than in other year through the entire irrigation period. Rapid rise in flux for early August and gradual decrease between late August and September were shown in 2013. Fluxes under drained condition showed larger emission than under flooded condition. Cumulative CH₄ emissions during cultivated period from 2011 to 2013 were estimated 15.7, 8.6, and 12.9 gC/m², respectively.