Article Summary: Rice cultivation is one of the leading contributors to atmospheric methane emissions, rivalling cattle and other ruminants as an atmospheric methane source. Methane is a highly potent greenhouse gas; rice grown in flooded paddies provides ideal conditions for microorganisms that produce it to do their work and contribute significantly more than estimated global methane emissions from farming operations. Recent studies show more emissions coming from rice cultivation than initially estimated. Some scientists now believe total emissions from rice may be similar to those from beef and dairy cattle on a gram-for-gram basis. This has implications for reducing methane and slowing climate change, suggesting that more initiatives should focus on changing rice-growing techniques instead of exclusively targeting livestock industries.

Understanding the facts: what is methane, and why is it bad?

Methane (CH4) is an alkane hydrocarbon gas with the chemical formula CH4. As the main constituent of natural gas and one of the easiest molecules to break down into usable energy forms, methane makes up roughly 85-90% of the volume of natural gas produced. It accounts for 80 times by value when measured over 20 years. Methane emissions come naturally from wetlands and human activities like cattle farming, rice cultivation, fossil fuel exploitation, and waste breakdown.

Approximately 8% of agricultural greenhouse gas emissions globally come from producing rice. Methane emissions produced through floodplain paddy fields account for 12% of anthropogenic methane emissions, comprising 1.5% of their warming impact.

The many sources of methane

Methane is a potent greenhouse gas and can be emitted from various sources. Here are some significant sources of methane:

  • Natural Sources

Wetlands account for roughly 30% of global methane emissions, including bogs, tundra, and freshwater habitats like lakes. Billions of microorganisms thrive here despite limited oxygen, producing methane as a by-product of decomposition processes.

  • Agriculture

Around 20% comes from livestock production, rice cultivation, and waste management. Ruminant animals such as cattle produce methane through belching and manure disposal, while anaerobic rice fields with methane-producing bacteria provide ideal conditions. Composting agricultural waste also adds significantly.

  • Fossil Fuel Extraction and Transport

About 30% is associated with fossil fuel exploitation, processing, transport, and use. Large amounts are released from coal mining, natural gas, and oil systems due to accidental leaks and deliberate venting or flaring of gas. Gas pipe networks and consumer use of gas for energy and heating also emit methane.

While beef production is a major contributor to atmospheric methane, it is not solely to blame. Rice farming is also a significant source of this potent greenhouse gas. 

As global agriculture strives to minimise its environmental impact, all methane-emitting activities must be addressed - including cattle and rice. You and consumers must collaborate on innovative solutions to curb emissions from all parts of the food system.

Researchers calculated that increasing rice farming in sub-Saharan Africa has led to significantly higher methane emissions. Using updated data on rice area growth since 2008, they found that this activity accounted for 31% of Africa's rise in methane emissions from 2006 to 2017.

For the same period, rice farming contributed 7% of the global methane increase. As rice production doubles the food supply but raises methane, sustainable agriculture practices are needed to curb emissions while ensuring regional food security.

The Eddy Covariance and Chamber methods of measuring methane emissions of rice paddies

The chamber method is commonly used to measure methane emissions from rice paddies. However, it only provides sporadic measurements from confined areas and may need to be more accurate. Meanwhile, the eddy covariance technique allows for continuous monitoring across open fields. However, measurement heights can impact results depending on soil conditions for this method.

Researchers conducted eddy covariance measurements at different heights in rice paddies in Korea in 2020-2021. They found height-related differences in measurements for the first time and proposed a correction method. Precise calibration was enabled using a methane reference gas developed by KRISS.

This represents the first application of an internationally recognised methane standard to rice paddy soil measurements. The findings could help verify national greenhouse gas inventory data by comparing chamber and eddy covariance methods. Improved accuracy and integrated global observation networks may also result from height correction techniques and mutual data validation between methods.

How rice plants could reduce methane emissions in rice paddies

Rice plants may be able to reduce methane emissions from rice paddies. Higher methane-emitting paddies tend to have lower contributions from rice-derived organic matter substrates. Instead, rice plants' contribution to oxygen is greater in those high-emitting fields.

This indicates that rice plants play a role in lowering methane levels. When methane emissions are high, the rice contributes more oxygen, which impacts the microbes producing methane in the soil. More oxygen from rice photosynthesis in heavily emitting paddies decreases the methane generated.

The findings show that rice plants can help reduce methane emissions, especially in paddies with high baseline emission levels. The oxygen input from rice counteracts methane-producing microbes under these conditions. This points to rice varieties or growing practices that maximise plant oxygen provision as a potential strategy for lowering greenhouse gas emissions from rice cultivation.

Beyond cattle: rice farming's unexpected methane footprint

This research demonstrates that rice agriculture is a more significant source of methane than previously estimated.

Accounting for rice field emissions shows they may rival or even surpass cattle. Global farmers and authorities must pay more attention to reducing pollution from rice cultivation through methods like alternate wetting and drying. 

Progress in this farming speciality will require inventory adjustments, improved measurement techniques, and incentive programs for you to adopt less emissions-intensive practices. Addressing methane from all major sources, including cattle production, is essential to slow climate change significantly.

Until we meet again, Happy Farming!

- The Dedicated Team of, 2024-02-13