Higher Methane Emission Rates in the Vegetative Rice Growing Stages in the Lower Mekong Delta, Vietnam

The Mekong Delta in Vietnam is a region that produces rice and emits methane, a potent greenhouse gas. Vietnam’s rice exports, which rank among the top four globally, have a significant impact on the world’s food suppy. The Eddy Covariance system, positioned in the rice field, has been recording methane emission rates and bio-meteorological factors. This study presents the findings of three crop seasons (Summer-Autumn 2020 (S-A20), Winter-Spring 2021 (W-S21), and Spring-Summer 2021 (S-S21)) from the year 2020 to 2021. The highest CH4 emission value was observed in the S-S21 crop, reaching 4.14 µmol s–1 m–2. Elevated CH4 emission rates were predominantly recorded during the vegetative stage within first 21 days after planting, while lower CH4 emissions were observed during the reproductive and ripening stages. This pattern clearly indicates higher methane emissions at the vegetative stage of the growing rice, likely due to the abundance of organic matter in the rice fields. The average CH4 emission rate was 0.1 µmol m–2 s–1 . Notably, high methane emissions were recorded when the soil surface temperature was below 33 °C. As a results, the S-S21 exhibits the highest methane emission rates compared to other seasons.