Greenhouse gases from irrigated rice systems under varying severity of alternate-wetting and drying irrigation

Authors: BALAINE, N. - University Of California, Davis; CARRIJO, D. - University Of California, Davis; Adviento-Borbe, Arlene; LINQUIST, B. - University Of California, Davis

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2019
Publication Date: 10/10/2019
Citation: Balaine, N., Carrijo, D., Adviento-Borbe, A.A., Linquist, B. 2019. Greenhouse gases from irrigated rice systems under varying severity of alternate-wetting and drying irrigation. Soil Science Society of America Journal. 83(5):1533-1541. https://doi.org/10.2136/sssaj2019.04.0113.
DOI: https://doi.org/10.2136/sssaj2019.04.0113

Interpretive Summary: The U.S. ranks 6th in major rice exporting countries in the world. Because rice is an important crop commodity in the U.S. economy, mitigation options should not negatively impact grain yields. Greenhouse gas mitigation strategies need to address reducing sustainable practices to reduce methane emissions while minimizing nitrous oxide emissions. Alternate wetting and drying (AWD) irrigation practice has shown potential to reduce methane emissions without yield penalty. This study demonstrated that the AWD practice reduced methane emissions in rice by 41 to 73% during the growing period. Drying of rice fields during the drained period was not beneficial for further reductions of methane emissions. Additional, drying the field for up to 13 days before re-flooding did not affect the grain yield. This information will benefit extension workers, rice breeders, crop consultants, and rice growers in adopting AWD to save water use, protect yields and trade carbon emissions in the Carbon Credit Marketplace.

Technical Abstract: Rice (Oryza sativa L.) is normally grown under flooded conditions and is a significant source of methane (CH4). Alternate wetting and drying (AWD) is one practice that is receiving a lot of attention and has shown promise to reduce CH4 emissions and global warming potential (GWP). Under AWD, the soil is allowed to dry periodically during the growing season. In this two-year field study, three different severities of drying were compared to a continuously flooded condition to quantify effects on rice yields, greenhouse gas emissions, GWP and yield-scaled GWP (GWPY). The AWD treatments in order of increasing drying severity were Safe-AWD (AWDS): treatment plots were reflooded when the perched water table fell 15 cm below the soil surface (AWDS) and AWD35 and AWD25 where plots were reflooded when the soil volumetric water content reached 35% and 25%, respectively. Each of these treatments received two drying cycles (all occurring between 45 days after planting and heading). Grain yields and N2O emissions (close to zero) did not vary among treatments. The AWDS reduced CH4 emissions by 41% and the AWD35 and AWD25 by 56-73% and 60-67%, respectively. Since only CH4 differed between treatments, AWD reduced GWP and GWPY by the same relative amount as CH4. Increasing drying severity reduced CH4, GWP and GWPY emissions up to a point (AWD35) but continued drying did not further reduce CH4 emissions. Given the high early season CH4 fluxes, draining earlier may result in greater reductions of CH4 in wet seeded rice systems but this requires further study as there may be negative effects such as increased N2O emissions.