Greenhouse gas flux monitoring in ecosystems is mostly conducted by closed chamber and eddy covariance techniques. To determine the relevance of the two methods in rice paddy fields at different growing stages, closed chamber (CC) and eddy covariance (EC) methods were used to measure the methane (CH₄) fluxes in a flooded rice paddy field. Intensive monitoring using the CC method was conducted at 30, 60 and 90 days after transplanting (DAT) and after harvest (AHV). An EC tower was installed at the centre of the experimental site to provide continuous measurements during the rice cropping season. The CC method resulted in CH₄ flux averages that were 58%, 81%, 94% and 57% higher than those measured by the EC method at 30, 60 and 90 DAT and after harvest (AHV), respectively. A footprint analysis showed that the area covered by the EC method in this study included non-homogeneous land use types. The different strengths and weaknesses of the CC and EC methods can complement each other, and the use of both methods together leads to a better understanding of CH₄ emissions from paddy fields.

Although bubble ebullition through water in rice paddy fields dominates direct methane (CH₄) emissions from paddy soil to the atmosphere in tropical regions, the temporal changes and regulating factors of this ebullition are poorly understood. Bubbles in a submerged paddy soil also contain high concentrations of carbon dioxide (CO₂), implying that CO₂ ebullition may occur in addition to CH₄ ebullition. We investigated the dynamics of CH₄ and CO₂ ebullition in tropical rice paddy fields using an automated closed chamber installed between rice plants. Abrupt increases in CH₄ concentrations occurred by bubble ebullition. The CO₂ concentration in the chamber air suddenly increased at the same time, which indicated that CO₂ ebullition was also occurring. The CH₄ and CO₂ emissions by bubble ebullition were correlated with falling atmospheric pressure and increasing soil surface temperature. The relative contribution of CH₄ and CO₂ ebullitions to the daily total emissions was 95–97% and 13–35%, respectively.

Separate evaluation of methane (CH₄) emission dynamics (e.g., oxidation, production, and transportation) at the soil‐plant‐atmosphere and soil‐water‐atmosphere interfaces has been limited in tropical rice paddies, but it is crucial for comprehending the entire CH₄ cycles. We investigated CH₄ oxidation, production, and transportation through plant and water pathways during the reproductive stage in a tropical Thailand rice paddy field using natural abundance carbon stable isotope ratios (δ¹³CH₄ and δ¹³CO₂). Mass balance equations using δ¹³CH₄ and δ¹³CO₂ in soil gases indicated that CH₄ oxidation in the planted soil exceeded those in the interrow soil due to oxygen supply through rice roots. In addition, at 1–11 cm depth acetate fermentation was the dominant process in the planted soil, whereas in the interrow soil the dominant process was H₂/CO₂ reduction. The water pathway showed a significant negative correlation between CH₄ flux and released δ¹³CH₄ over 24 hr, driven by a diel change in episodic ebullition, steady ebullition, and diffusion, all due to diel changes in soil temperature and atmospheric pressure. In contrast, the plant pathway showed a significant positive relationship between CH₄ flux and emitted δ¹³CH₄ throughout one day. A comparison of the diel change in emitted δ¹³CH₄ between the water and plant pathways showed that the rice plants transported CH₄ in soil bubbles without any large isotopic fractionation. The diel change in the plant‐mediated CH₄ transportation was mainly controlled by diel changes in soil bubble expansion and CH₄ diffusion through plants, which were probably regulated by diel changes in soil temperature and atmospheric pressure.

Greenhouse gas (GHG) emissions from paddy fields depend on water management practices and rice varieties. Lysimeter experiments were conducted to determine the effect of rice varieties (lowland; Koshihikari (KH) and upland; Dourado Precoce (DP)) on GHG emissions under two water management practices: alternate wetting and drying (AWD) and continuous flooding (CF). A repeated cycle of drying and wetting in AWD irrigation was performed by drying the soil to −40 kPa soil matric potential and then rewetting. Consequently, the closed chamber method was used to measure direct emissions of methane (CH₄), nitrous oxide (N₂O), and carbon dioxide (CO₂). The result revealed that water management significantly affected CH₄ and N₂O emissions (p < 0.05), while no significant effect was observed between different rice varieties. Although, AWD irrigation reduced CH₄ emissions, it increased N₂O emissions compared to CF irrigation, likely due to increased oxygen supply. AWD irrigation decreased GWP by 55.6% and 59.6% in KH and DP, respectively, compared to CF irrigation. Furthermore, CH₄ and N₂O emissions significantly correlated with soil redox potential and volumetric water content. These results suggest that AWD irrigation might be an effective water management method for mitigating GHG emissions from rice fields in central Japan.

For agricultural purposes, the drainage and deforestation of Southeast Asian peatland resulted in high greenhouse gases’ (GHGs, e.g., CO₂, N₂O and CH₄) emission. A peatland regenerating initiative, by rewetting and vegetation restoration, reflects evidence of subsequent forest recovery. In this study, we compared GHG emissions from three Malaysian tropical peatland systems under the following different land-use conditions: (i) drained oil palm plantation (OP), (ii) rewetting-restored forest (RF) and (iii) undrained natural forest (NF). Biweekly temporal measurements of CO₂, CH₄ and N₂O fluxes were conducted using a closed-chamber method from July 2017 to December 2018, along with the continuous measurement of environmental variables and a one-time measurement of the soil physicochemical properties. The biweekly emission data were integrated to provide cumulative fluxes using the trapezoidal rule. Our results indicated that the changes in environmental conditions resulting from draining (OP) or rewetting historically drained peatland (RF) affected CH₄ and N₂O emissions more than CO₂ emissions. The cumulative CH₄ emission was significantly higher in the forested sites (RF and NF), which was linked to their significantly higher water table (WT) level (p < 0.05). Similarly, the high cumulative CO₂ emission trends at the RF and OP sites indicated that the RF rewetting-restored peatland system continued to have high decomposition rates despite having a significantly higher WT than the OP (p < 0.05). The highest cumulative N₂O emission at the drained-fertilized OP and rewetting-restored RF sites was linked to the available substrates for high decomposition (low C/N ratio) together with soil organic matter mineralization that provided inorganic nitrogen (N), enabling ideal conditions for microbial mediated N₂O emissions. Overall, the measured peat properties did not vary significantly among the different land uses. However, the lower C/N ratio at the OP and the RF sites indicated higher decomposition rates in the drained and historically drained peat than the undrained natural peat (NF), which was associated with high cumulative CO₂ and N₂O emissions in our study.