Understanding the nature of methane emission from rice ecosystems as basis of mitigation strategies

Methane is considered an important greenhouse gas and rice fields are one of the major atmospheric methane sources. This paper develops sampling strategies and formulates mitigation options based on diel (day and night) and seasonal patterns of methane emissions. The design of sampling strategies and identification of abatement strategies were based on data obtained using automatic closed-chamber systems. Diel patterns of methane emissions from irrigated rice fields displayed similar patterns from planting to flowering. Fluxes at 0600, 1200, and 1800 h were important components of the total diel flux. Methane fluxes sampled during these times are sufficient to capture most of the diel variation observed throughout the growing season. Seasonal patterns of methane emissions indicated the intensity of flux measurement that should be done within the growing season. The characterization of seasonal emission patterns according to ecologies, fertilizer amendments, and water management provides a focus for mitigation strategies. Mitigation strategies, based on seasonal patterns, may be grouped into two approaches: preventive measures and reducing measures. Preventive measures may take into consideration, prior to planting rice, the ecology and fertilizer management that will give fewer methane emissions. Reducing measures become necessary when the option to prevent high emissions is not possible under a given condition. Other factors may be considered as preventive or reducing measures to mitigate methane emission. These factors, however, should be evaluated as to how they influence the diel and seasonal patterns of methane emission. Two things can be derived from the evaluation: (i) an improvement of the emission factor for better extrapolation; and (ii) a better understanding of how and when mitigation strategies can best be applied. (C) 1997 Elsevier Science Ltd.