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Rice Methane Emissions


Methane (CH4) is a potent greenhouse gas (GHG) which global warming potential is 28-34 times higher than that of carbon dioxide (CO2) over a 100-year time period. Viewed within a 20-year period, its power becomes 84 times higher at a par unit mass of CO2. Therefore, the spotlight is on reducing CH4 emissions to mitigate climate change. Given that Paris agreement on limiting the global temperature increase to 1.5 0C, it was pledged by the global partnership in COP-26 to cut CH4 emissions by 30% by 2030 compared to 2020. One of the major anthropogenic sources of CH4 emission is rice (oryza sativa L.) cultivation which contributes nearly 10% of global CH4 emissions. Rice CH4 emissions in 2010 was 1,120 Mt CO2-eqivalent /yr and projected to increase 1,696 Mt/year by 2050.

As one of the staple foods, rice feeds half of the global population every day. To meet the food demand of a growing population, the harvested area has now increased to 162 Mha, occupying 12% of world’s arable land, mainly in Asia. China, India, Indonesia, Bangladesh, Vietnam, Myanmar, and Thailand are the major dominant rice-producing countries. Therefore, challenges remain in addressing food security using limited natural resources whilst improving soil health and mitigating the climate change impact.

Conventional continuous flooding (CF) management in paddy fields leads to anaerobiosis by preventing atmospheric O2 to enter the soil. Methane is produced by decomposing soil organic matter with the process of methanogenesis. Methane is released to the atmosphere mostly via rice plants and small portions through ebullition and diffusion in the paddy water. Besides flooding conditions, soil temperature, soil pH, rice cultivar and straw incorporation are the main factors influencing CH4 productions in paddy ecosystems.

Fortunately, there are clear interventions which mitigate CH4 emissions from paddy soil whilst supporting food security and improving livelihoods. Selection of suitable rice cultivars (e.g high yielding and salt tolerant varieties) and improved fertilizer management are two suggested options to reduce CH4 emission from paddy rice thereby contributing to lower global warming. However, alternate wetting and drying (AWD) is generally identified as the most promising solution which is environmentally and economically friendly. In place of CF, reducing flooding state by AWD tends to decrease CH4 producing bacteria and leads to up to 93% lower CH4 emissions. Adoption of AWD would additionally save water in the dry regions of Asia, where water scarcity is one of the major environmental problems. However, promoting and monitoring the adoption of agricultural management changes such as AWD from local to continental scale is challenging.

Geotree facilitates nature-based solutions in rice ecosystems by supporting project implementation while significantly reducing the costs for monitoring, reporting and verification (MRV). Geotree’s cost-efficient, scalable and reliable MRV solutions build on suitable process-based models coupled with remotely sensed data. This allows policy makers, farmers, carbon credit buyers and other stakeholders to understand the alternative management strategies which reduce CH4 emissions and thereby contribute significantly to GHG mitigation within agriculture.