Understanding the major controlling factors of methane emissions from ricefields is critical for estimates of source
strengths. This paper reports results on the relationship of different plant characteristics and methane fluxes in
ricefields.
Methane fluxes in ricefields show distinct diel and seasonal variations. Diel variations are mainly controlled by
soil solution temperature and the partial pressure of methane. One or two distinct seasonal maxima are observed in
irrigated ricefields. The first is governed by methane production from soil and added organic matter and a second
at heading is plant derived. During ripening and maturity, root exudation, root porosity and root oxidation power
may control methane emission rates. Rice plants play an important role in methane flux. The aerenchyma conduct
methane from the bulk soil into the atmosphere. The amount of carbon utilized in methane formation varied among
cultivars. A strong positive effect of rice root exudates on methane production imply that cultivar selections for
lower methane emissions should not only be based on the gas transport capabilities but also on the quality and
quantity of root exudates.
Soils show a wide range of methane production potential but no simple correlation between any stable soil
property and methane production is evident. Various cultural practices affect methane emissions. Defined aeration
periods reduce methane emissions. Soil entrapped methane is released to the atmosphere as a result of soil
disturbances. Mineral fertilizers influence methane production and sulfate containing fertilizer decrease methane
production. The methane release per m2 from different rice ecosystems follow the order: deepwater rice>irrigated
rice>rainfed rice. Abatement strategies may only be accepted if the methane source strength of ricefields is reliably
discriminated and if mitigation technologies are in accordance with increased rice production and productivity