A Bloomberg report titled Mysterious Plumes of Methane Gas Appear Over Bangladesh, published on Apr. 8, 2021, identified Bangladesh as the 12th largest methane emitter, attributing a significant share to rice cultivation. The report eventually concerned the local rice researchers.
Equipped with only secondary and manually collected data, they challenged the ‘exaggerated’ claim, arguing that methane emission from Bangladesh’s rice production was relatively small compared to its neighbors India and China—the major emitters.
Although, Bloomberg published another report two weeks later, claiming that a leaking municipal solid waste landfill contributed to the mysterious methane plumes, researchers at Bangladesh Rice Research Institute (BRRI) looked forward to advanced technology to have concrete and real-time emission measurement data to counter such exaggerated’ assessments.
On Sep. 4, 2024, BRRI researchers introduced Bangladesh’s first greenhouse gas (GHG) emission monitoring laboratory at its regional office in Barishal district’s Sagardi area with the support of development partners.
This new installation also aims to support research on the emission-cutting Alternate Wetting and Drying (AWD) method that the BRRI researchers have been piloting in Bangladesh’s rice fields for several years.
AWD is an irrigation method that reduces water use in rice fields without disturbing the plant's growth, germination, and other processes to mature the rice.
“Given the real-time GHG emission measurement facilities, we would not only analyze the impacts of AWD but also claim carbon credits someday,” BRRI Director General Muhammad Khalequzzaman tells Mongabay, adding that a rice field emits greenhouse gases and adsorbs carbon dioxide as well.
According to BRRI researchers, the GHG emission measurement laboratory is equipped with automated systems that collect and analyze real-time emissions of methane (CH4), carbon dioxide (CO₂), and nitrous oxide (N₂O). They believe that such a critical advancement in the country’s efforts to quantify and analyze GHG emissions from rice cultivation will facilitate more effective research into mitigation techniques.
The Laboratory
In a recent visit to the BRRI regional office in Sagardi area, we observed that some plastic jars were placed at different paddy plots prepared with poultry litter and chemical fertilizers usually applied for rice cultivation.
The Barishal regional chief of BRRI and principal scientific officer, Mohammad Ashik Iqbal Khan, explained how the GHG emission measurement machines, manufactured by LI-COR Environmental, work.
“The chamber bowls seal the plastic jars for two minutes, measure the emitted gases, and send the real-time information to the computers,” Ashik said, sitting beside a tin-shed laboratory where the computers were placed.
A GHG measurement machine works by using a sealed chamber to measure gas exchange, like CH4 uptake and water vapor release, from a plant leaf. Simultaneously, it measures chlorophyll fluorescence to provide detailed information about the plant's photosynthetic activity, according to LI-COR.
The AWD method was applied to all of the rice research plots. However, the GHG measurement machines were placed on different plots to analyze the contribution of fertilizers to GHG emissions, Ashik explained.
“This laboratory represents a significant leap from the manual measurement methods previously used, where emissions were assessed only once every seven days,’ Ashik said.
Methane emissions from a rice field
A study finds that about 60% of the global methane is emitted from anthropogenic sources, whereas 40% of the emissions come from natural sources.
The major natural sources of methane are wetlands and oceans, termites, wildfires, and grasslands. A study traces the major anthropogenic sources, including enteric fermentation in ruminants, anaerobic decay of organic matter in rice paddies, municipal solid waste landfills, cattle ranching, and manure management.
The same study states that the agricultural sector contributes the highest amount of methane, while a 2021 study finds around 30% of global agricultural methane is emitted from rice fields.
Methane is generated in rice fields through various processes, with the primary mechanism being the microbial breakdown of organic compounds under strictly anaerobic conditions typically present in rice cultivation.
Under these conditions, methanogenic bacteria utilize carbon substrates, including freshly added organic matter and root exudates, for their growth and development. The incomplete decomposition of organic matter in the anaerobic environment produces methane by generating several intermediate compounds such as hydrogen or carbon dioxide, methanol, methylamines, and acetate.
However, a significant portion of the methane produced is oxidized by methanotrophs—obligate aerobic bacteria—before it escapes into the atmosphere. This oxidation primarily occurs at the anaerobic interfaces, such as the oxygenated soil surface, oxygenated water layers, and areas surrounding the oxygen-releasing roots of rice plants.
Quantifying methane emission and AWD
A study on methane emissions from rice production identifies several hotspots. These include the Yangtze River Basin which covers one-fifth of the land area of China, a large portion of south western Vietnam in the Deltas of the Mekong, and the Indo-Gangetic Plain which spans northern and eastern India, eastern Pakistan, southern Nepal and almost all of Bangladesh.
In these regions, China, India, Bangladesh and Vietnam are the major rice-producing countries.
Bangladesh produces about 39.1 million metric tonnes of rice annually, and rice cultivation covers around 76% of the country's cropped land. Noteworthy that Bangladesh's Nationally Determined Contribution (NDC) includes actions to reduce methane emissions from agriculture and other sources.
Even before introducing NDC in Bangladesh, BRRI researchers launched the promotion of AWD in 2005, with field trials. Instead of keeping fields continuously flooded, AWD involves periodic drainage, which reduces anaerobic conditions and subsequently limits methane production.
Recognizing its potential, the Bangladesh Government included AWD expansion as a key climate action strategy in its NDC to implement this method on 50,000 hectares of cropland.
However, BRRI researchers observed that deficiency in Bangladesh-specific GHG emission factors from rice fields compelled them to rely on some limited and manual data or default emission factors set by the Intergovernmental Panel on Climate Change.
They felt the importance of determining baseline data on GHG emissions for rice cultivation across different agroecological zones and management practices.
BRRI’s Senior Scientific Officer S M Mofijul Islam thinks that the GHG emission measurement laboratory will generate precise data and the integration of AWD with it will provide crucial insights into the method’s effectiveness in different agroecological zones of Bangladesh and other countries with similar agroecology, soil type, and management practices.
With manual investigation, a study by Mofijul and other researchers found that AWD irrigation significantly reduced cumulative methane emissions (37% average across sites) without affecting grain yields compared to the continuous flooding method.
“By closely monitoring real-time methane emissions under various conditions, we can now refine AWD techniques to maximize their impact,” Mofijul says.
BRRI chief Muhammad Khalequzzaman tells Mongabay that the GHG emission measurement machines would be replicated in other rice production zones in Bangladesh in 2026 as part of the ongoing research.
Citations
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Yusuf, R. O., Noor, Z. Z., Abba, A. H., Hassan, M. A. A. & Din, M. F. M. (2012). Methane emission by sectors: A comprehensive review of emission sources and mitigation methods; Renewable and Sustainable Energy Reviews, Volume 16, Issue 7, Pages 5059-5070, ISSN 1364-0321.
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Gupta, K., Kumar, R., Baruah, K.K., Hazarika, S., Karmakar, S. & Bordoloi, N. (2021). Greenhouse gas emission from rice fields: a review from Indian context. Environmetal Science and Pollution Research.
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Zhou, H., Tao, F., Chen, Y., Yin, L., Li, Y., Wang, Y. & Su, C. (2024). Paddy rice methane emissions, controlling factors, and mitigation potentials across Monsoon Asia, Science of The Total Environment, Volume 935, ISSN 0048-9697
DOI: https://doi.org/10.1016/j.scitotenv.2024.173441
Islam, S. M. M., Gaihre, Y. K., Islam, M. R., Akter, M., Mahmud, A. A., Singh, U. & Sander, B. O. (2020). Effects of water management on greenhouse gas emissions from farmers' rice fields in Bangladesh; Science of The Total Environment; Volume 734, ISSN 0048-9697
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