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Proc Natl Acad Sci U S A. 2018 Sep 10. pii: 201809276. doi: 10.1073/pnas.1809276115. [Epub ahead of print]

High nitrous oxide fluxes from rice indicate the need to manage water for both long- and short-term climate impacts.

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Environmental Defense Fund, New York, NY 10010;
Environmental Defense Fund, New Delhi 110001, India.
Fair Climate Network, Bagepalli 561 207, Karnataka, India.
Environmental Defense Fund, New York, NY 10010.
School of Biotechnology, Kalinga Institute of Industrial Technology, Bhubaneswar 751 024, Odisha, India.
University of Kansas, Lawrence, KS 66045.
Accion Fraterna Ecology Centre, Anantapur 515 003, Andhra Pradesh, India.
Bharath Environment Seva Team, Pudukkottai 622 101, Tamil Nadu, India.
Palmyrah Workers Development Society, Tirunelveli 627 452, Tamil Nadu, India.
Timbaktu Collective, Chennekothapalli 515 101, Andhra Pradesh, India.


Global rice cultivation is estimated to account for 2.5% of current anthropogenic warming because of emissions of methane (CH4), a short-lived greenhouse gas. This estimate assumes a widespread prevalence of continuous flooding of most rice fields and hence does not include emissions of nitrous oxide (N2O), a long-lived greenhouse gas. Based on the belief that minimizing CH4 from rice cultivation is always climate beneficial, current mitigation policies promote increased use of intermittent flooding. However, results from five intermittently flooded rice farms across three agroecological regions in India indicate that N2O emissions per hectare can be three times higher (33 kg-N2O⋅ha-1⋅season-1) than the maximum previously reported. Correlations between N2O emissions and management parameters suggest that N2O emissions from rice across the Indian subcontinent might be 30-45 times higher under intensified use of intermittent flooding than under continuous flooding. Our data further indicate that comanagement of water with inorganic nitrogen and/or organic matter inputs can decrease climate impacts caused by greenhouse gas emissions up to 90% and nitrogen management might not be central to N2O reduction. An understanding of climate benefits/drawbacks over time of different flooding regimes because of differences in N2O and CH4 emissions can help select the most climate-friendly water management regimes for a given area. Region-specific studies of rice farming practices that map flooding regimes and measure effects of multiple comanaged variables on N2O and CH4 emissions are necessary to determine and minimize the climate impacts of rice cultivation over both the short term and long term.


alternate wetting and drying; methane; nitrous oxide; rice; water

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Conflict of interest statement

The authors declare no conflict of interest.

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