Paddy fields are significant anthropogenic sources of methane (CH₄) emissions. In southern Brazil, rice is grown in lowland flooded areas once a year, followed by a long fallow period. This study aimed to measure CH₄ fluxes in a rice paddy field in southern Brazil during the rice-growing season of 2015/2016 and the following fallow period. The fluxes were estimated using the eddy covariance (EC) technique and soil chamber (SC). Diurnal and seasonal variations of CH₄ fluxes and potential meteorological drivers were analyzed. The CH₄ fluxes showed distinct diurnal variations in each analyzed subperiod (vegetative, reproductive, pre-harvest, no rice, and land preparation), characterized by a single-peak diurnal pattern. The variables that most influenced methane emissions were air and surface temperatures. In the growing season, the rice vegetative stage was responsible for most of the measured emissions. The accumulated annual emission estimated was 44.88 g CH₄ m⁻² y⁻¹, being 64% (28.50 g CH₄ m⁻²) due to the rice-growing season and 36% (16.38 g CH₄ m⁻²) due to the fallow period. These results show the importance of including fallow periods in strategies to mitigate methane emissions in flood irrigated rice-growing areas.

Studies on the emission of methane gas (CH4) in agricultural ecosystems have received attention from the scientific communitybecause it plays an important role in the greenhouse effect. Flood irrigation agriculture, such as irrigated rice, represents aconsiderable source of methane emissions (from 12 to 26 percent of all anthropogenic CH4 emissions in the world). Estimates ofCH4 emissions have also been performed through the eddy covariance technique. Although this methodology makes continuousmeasurements of methane exchanges between the ecosystem and the atmosphere, failure to collect data can occur because thesystem is quite sensitive, especially in the hard weather conditions. The gap filling in the methane data are essential to obtaina daily or seasonal quantification of the emissions. In this study, different gap filling techniques are used to fill the CH4 fluxesobtained by eddy covariance technique in an irrigated rice crop. The experimental data were obtained in Cachoeira do Sul - RS inthe period from 11/20/2015 to 04/30/2016. The Look-Up Table (LUT), which consists of filling gaps using averages of flux valuesfor periods with similar atmospheric conditions, was the technique that best close the gap in methane fluxes data.