Greenhouse Gas Emissions and Rice Farming

June 29, 2015

chart of how rice farming produces greenhouse gases

The Intergovernmental Panel on Climate Change (IPCC) has confirmed that anthropogenic emissions of greenhouse gases (GHGs), which are those emitted by human activity, contribute to climate change and are at their highest levels in history. GHGs contribute to the warming of the planet by trapping radiation and releasing it near the surface of the earth. Agricultural practices emit over 50% of global non-carbon dioxide GHG emissions. About 7% of these emissions are a result of rice farming, and over 80% of GHG emissions from rice farming are produced in South and Southeast Asia (India, China, Indonesia, Thailand, Vietnam, and Burma).

The warming of the planet, combined with the growing population expected to exceed 9 billion by 2050, threaten advancements made to achieve global food security and environmental sustainability. To address this challenge, the AgResults Vietnam GHG Emissions Reduction Pilot aims to identify novel approaches for reducing GHG emissions while increasing yields in rice cultivation, and to scale the most effective approaches to thousands of smallholder farmers.

The earth’s surface, like all planetary bodies, releases infrared radiation. While this radiation usually travels through the atmosphere and escapes the surface, greenhouse gases (GHGs) that are present in the atmosphere, such as carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and even water (H2O), can capture this radiation and release it back to the surface of the earth.

GHGs are emitted as a byproduct of many activities such as burning fossil fuels, generating electricity, and agriculture. While CO2 is often the first one that comes to mind, CH4 and N2O are much stronger contributors of GHGs emissions.

chart showing the strength of different greenhouse gases

Rice farming is a significant source of human-produced non-COemissions. Because rice is grown in flooded systems, the soil remains waterlogged, preventing oxygen from entering the pores.  Additionally, the decomposition of organic plant matter in the fields consumes and therefore, limits the amount of oxygen present. With limited oxygen in the soil, bacteria that can conduct anaerobic respiration, or “breathing” in the absence of oxygen, thrive.

chart

Two of the most common methods of such respiration in flooded rice fields are methanogenesis, the production of CH4, and denitrification, the conversion of nitrates to nitrogen gas with N2O as a byproduct (see infographic on methanogenesis and denitrification). Paddy rice fields are particularly conducive to these processes not only because the soil is waterlogged and therefore lacks oxygen; but also because anaerobic bacteria rely on plant matter from rice for respiration.

Traditional methods of rice farming, like those practiced in the Southeast Asia, contribute to greater GHG emissions than in other regions. These methods include constant saturation of rice fields (which depletes oxygen in the system), the addition of fertilizers (which provides nitrates that stimulate denitrification in bacteria), and increasing the acreage of rice fields (which increases the area available for GHG emissions).

Alternate methods such as modified irrigation and more efficient fertilizer use have proven to be effective in reducing GHG emissions. However, getting buy-in from growers poses a challenge to widespread implementation of GHG-reducing practices due to limited outreach and awareness regarding the incentives and benefits of alternate methods of rice farming. To identify and improve ways of increasing rice yields while simultaneously reducing GHG emissions, AgResults will implement a pilot project to encourage smallholder farmers in Vietnam to adopt agronomic practices, tools and technologies that lower GHG emissions in rice production.

“SRI International Network and Resources Center.” Link: http://sri.cals.cornell.edu/

 “Global Anthropogenic Non-CO2 Greenhouse Gas Emissions: 1990 – 2030.” Revised December 2012. The U. S. Environmental Protection Agency. Link: http://www.epa.gov/climatechange/Downloads/EPAactivities/EPA_Global_NonCO2_Projections_Dec2012.pdf

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