Changsheng Li, a professor of natural resources in the University of New Hampshire's Institute for the Study of Earth, Oceans, and Space, and lead author of the study, notes that in the early 1980s Chinese farmers began draining their paddies midway through the rice growing season when they learned that replacing a strategy of continuous flooding would in fact increase their yields and save water. As an unintended consequence of this shift, less methane was emitted out of rice paddies.

Methane is 21 times more potent as a greenhouse gas than carbon dioxide (CO2) over 100 years. At the same time, since 1750, methane concentrations in the atmosphere have more than doubled, though the rate of increase has slowed during the 1980-90s.

"There are three major greenhouse gases emitted from agricultural lands-carbon dioxide, methane and nitrous oxide," said Li. "Methane has a much greater warming potential than CO2, but at the same time, methane is very sensitive to management practices." Currently, about 8 percent of global methane emissions come from the world's rice paddies.

In an effort to reduce water use, farmers in China found that if they drained the soils, they could get higher yields. That's because draining stimulates rice root development, and also accelerates decomposition of organic matter in the soil to produce more inorganic nitrogen, an important fertilizer. Methane is produced by soil microbes in paddy soils under anaerobic conditions, or in the absence of air or free oxygen. Midseason drainage aerates the soil again, and hence interrupts methane production.

Li and his colleagues recorded reductions in methane caused by draining practices at several experimental sites in China a
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Contact: Krishna Ramanujan
kramanuj@pop900.gsfc.nasa.gov
301-286-3026
NASA/Goddard Space Flight Center
19-Dec-2002