We thank R.W. Dalluge and D. Steams at OGI, Ren Lixin at the Institute of Atmospheric Physics (CAS) in Beijing, and Duan Chang-Lin at the Institute of Mountain Disasters and Environment in Chengdu for their contributions to this project. Additional support was provided by the Biospherics Research Corporation and the Andarz Co. This project was supported by the U.S. Department of Energy (DE-FG06-85ER60313).
Journal of Geophysical Research -- Atmospheres
Methane -- Environmental aspects, Rice -- Propagation -- Asia, Greenhouse gases
The emission of methane from rice fields is the difference between the amount produced in the anaerobic zone below the soil and the amount oxidized in the root zone. Plants can also contribute to methane production by exuding organic compounds that may be utilized by methanogenic bacteria. We measured methane emissions from rice fields at Tu Zu in China between 1988 and 1994, which gave average emissions of about 30 mg m⁻² h⁻¹. We estimate that 45-60% of the methane produced was oxidized before reaching the atmosphere; and root exudates may have contributed of the order of 10% of the methane that was produced. The fraction of methane oxidized is low compared to experimental studies at other locations (60-85%). At Tu Zu, methane production is enhanced by continuously flooded fields and the use of large amounts of organic fertilizers; in addition, the lower oxidation rate may also contribute to the higher methane emissions observed compared to other locations. In the past, most of the attention has been devoted to the factors that affect methane production and transport, but it seems that the factors that affect methane oxidation are equally important in determining the flux, if not more so. The comparison of methane fluxes observed at different locations and the extrapolation of field measurements to accurately estimate global emissions will require a better understanding of the rate of methane oxidation in the soils and the factors that control it.
Khalil, M. A. K., R. A. Rasmussen, and M. J. Shearer (1998), Effects of production and oxidation processes on methane emissions from rice fields, J. Geophys. Res., 103(D19), 25,233–25,239, doi:10.1029/98JD01116.