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Greenhouse gas emissions on rice farms underestimated, study finds

Because nitrous oxide persists in the atmosphere for longer than methane, the greenhouse gas has a greater warming impact.

By Brooks Hays
Greenhouse gas emissions on rice farms underestimated, study finds
The world's largest rice producers, China, India, Indonesia, Vietnam and Bangladesh, as well as the United States, don't report rice farming-related nitrous oxide emissions to the United Nations. Photo by Rakesh Tiwari/EDF

Sept. 10 (UPI) -- Climate scientists and policy makers have underestimated the amount of greenhouse gas emitted by rice farms. New research showed rice farms emit significant amounts of nitrous oxide in addition to methane.

In recent years, policy makers have worked with rice farmers to reduce methane emissions and conserve water resources by deploying intermittent flooding. As water resources become more scarce, more continually flooded rice farms are likely to adopt intermittent flooding methods.

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But new research -- published this week in the journal Proceedings. of the National Academy of Sciences -- suggests the reduction in methane emissions achieved by intermittent flooding is undermined by increases in nitrous oxide emissions.

"Water management on rice farms needs to be calibrated to balance water use concerns with the climate impacts of both methane and nitrous oxide emissions," Kritee Kritee, senior scientist at the Environmental Defense Fund, said in a news release.

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The world's largest rice producers, China, India, Indonesia, Vietnam and Bangladesh, as well as the United States, don't report rice farming-related nitrous oxide emissions to the United Nations. As a result, rice farming-related nitrous oxide emissions could be underestimated by a factor of 30 to 45.

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"It is essential for scientists to measure both nitrous oxide and methane emissions from rice fields in order to develop policies effective at meeting food demand while mitigating rice farming's climate impacts," Kritee said.

Because nitrous oxide persists in the atmosphere for longer than methane, the greenhouse gas has a greater warming impact. And because the intermittent flooding is more common than many studies estimate, scientists believe the impact of rice cultivation on the climate is being underestimated.

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"It is crucial that the climate impacts of rice cultivation are determined and lowered over both the long and short term," researchers wrote in a blog post.

Previous studies have shown more moderate nitrogen inputs combined with irrigation systems can help significantly reduce nitrous oxide emissions from rice farms.

"We now know nitrous oxide emissions from rice farming can be large and impactful," said researcher Richie Ahuja. "We now also know how to manage the problem. Major rice-producing nations in Asia are investing to improve the agriculture sector and could benefit from the suggested dual mitigation strategies that lead to water savings, better yields and less climate pollution."

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