Rice wins methane reduction battle
Researchers find California growers better at reducing greenhouse gas
By TIM HEARDEN
DAVIS, Calif. -- Researchers who published a recent study on rice paddies and climate change say California producers appear to be doing better than the rest of the world at reducing greenhouse gas emissions.
An international panel that includes a University of California-Davis plant scientist wrote in the journal Nature Climate Change that methane from rice paddies accelerates global warming, but relatively simple changes in cultivation practices can reduce emissions.
The available data suggest that per-area emissions in California may be a bit lower than average, perhaps because of a variety of factors, the study's lead author told the Capital Press in an email.
Factors could include the rice variety or soils, as heavy clays tend to emit less than coarse textured soils, explained Kees Jan van Groenigen, a research fellow at Trinity College Dublin in Ireland.
"(W)hen we express CH4 (methane) emissions per kg of rice yield, California rice systems look very good," van Groenigen said. "This is because California rice systems have some of the highest ... yields in the world. So, assuming per-acre CH4 emissions in California are similar to elsewhere, then CH4 emissions per kg of yield would be lower in California."
Van Groenigen cautioned that methane data is "highly variable" and there are relatively few California studies, so it would be premature to conclude definitively that the state's emissions are lower.
Van Groenigen conducted the research with Chris van Kessel, a professor of plant sciences at UC-Davis, and Northern Arizona University professor Bruce Hungate. The study was funded by the U.S. Department of Energy's National Institute for Climate Change Research, the Irish Research Council and other organizations.
The scientists gathered findings from 63 different experiments on rice paddies, mostly in Asia and North America. Paddy fields -- growing rice plants amid a flooded landscape -- are considered one of the largest man-made sources of methane.
The scientists used meta-analysis to measure how rising temperatures and extra carbon dioxide in the atmosphere affect both rice yields and the amount of methane released by the paddies, a UC-Davis news release explained.
They found that as more carbon dioxide enters the atmosphere, rice plants grow faster, which in turn produces more methane.
Charley Mathews, a Marysville, Calif., grower who chairs the California Rice Commission, said he was aware of the study and added industry research is ongoing to mitigate impacts on the environment.
"We're aware of it, but it depends on what goes on in the rest of the world," Mathews said. "I don't know if our practices are bigger than anyone else's practices."
The study's authors suggest management practices such as mid-season drainage and using alternative fertilizers -- the latter of which California producers appear to already be doing.
They typically apply aqua-ammonia injected in a band about 5 to 10 centimeters below the soil surface, which has been shown to reduce emissions, van Groenigen said.
Increased Greenhouse-Gas Intensity of Rice Production Under Future Atmospheric Conditions: http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1712.html