Abstract
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.
Highlights
Methane (CH4 ) is one of the main greenhouse gases (GHG) and has a heating potential28 times higher than carbon dioxide (CO2 ) [1]
To complete one year of data, we extrapolated the results of the period measured in situ with eddy covariance (EC), which we considered with similar soil cover and environmental conditions, using the mean value of each period
The maximum daily to air (Tair) was verified during the summer (27.9 ◦ C), and the minimum Tair was determined during the winter (4.8 ◦ C)
Summary
Methane (CH4 ) is one of the main greenhouse gases (GHG) and has a heating potential28 times higher than carbon dioxide (CO2 ) [1]. Flooded rice fields are responsible for 11–26% of the total anthropogenic CH4 emissions and emit around 30–40 Tg CH4 per year, with Asia accounting for 90% of emissions [1]. These rice are generally grown in lowland areas and are major sources of CH4 emissions [7,8]. In Brazil, 11.2 million tons of rice were produced in 2020 in a 1.67 million ha area [9], representing approximately 2.0% of world production [10]. In the 2019/2020 rice season, Rio Grande do Sul State, southern state of Brazil, produced about 8 million tons of rice in a 0.94 million ha area [11], in which river lowlands were developed to increase rice production
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