"The full climate impact of rice farming has been significantly underestimated because up to this point, nitrous dioxide emissions from intermittently flooded farms have not been included," said Kritee, Ph.D., senior scientist at EDF and the lead author of the paper. "Increasing pressure on limited water resources under a changing climate could make additional rice farming regions look to intermittent flooding to address water limitations and concerns about methane 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."
To monitor and mitigate rice farming's nitrous oxide impact, the authors call on 1) scientists to map flooding regimes and measure nitrous oxide emissions at a diversity of rice farms across the world; 2) countries to report these emissions; and 3) rice producers to optimize water, nitrogen and organic matter use to reduce emissions of these two important greenhouse gases.
"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," said Kritee.
Rice is a critical source of nutrition for the world's rapidly growing population, providing more calories to humans than any other food. But growing rice is also resource-intensive: rice cultivation covers 11% of the earth's arable land, consumes one-third of irrigation water.
Most studies on the climate impacts of rice have measured methane emissions from continuously flooded rice farms. In addition, current climate mitigation strategies for rice production focus on reducing methane emissions by alternate wetting and drying, or intermittent flooding. Most rice producing countries – including the Unites States and the world's biggest producers of rice (China, India, Indonesia, Vietnam and Bangladesh) – do not report nitrous oxide emissions associated with rice production as part of their national greenhouse gas inventories submitted to the United Nations.
The findings of today's study suggest that under intermittent flooding nitrous oxide emissions from rice farms across the world might be 30 to 45 times the maximum of current estimates, equivalent to annual climate pollution from 200 coal power plants to our atmosphere without accounting for methane emissions.
"We now know nitrous oxide emissions from rice farming can be large and impactful," said Richie Ahuja, a co-author of this study. "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."
Note: Access to an embargoed copy of the study is available to journalists via EurekAlert. Please register or access your account here. The name of the study is "High nitrous oxide fluxes from rice indicate the need to manage water for both long- and short-term climate impacts"
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