Chinese rice farmers reduce methane emissions from paddies by 40%

Changes in farming practices in rice paddies in China could have reduced methane emissions 40% in 20 years, - that’s five million metric tonnes per year, or roughly equivalent to the global decrease in the rate of growth of methane emissions, according to a study funded by NASA.

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. An unintended and added bonus of this practice was that the paddies emitted less methane – which is 21 times more potent as a greenhouse gas than carbon dioxide.

There are three major greenhouse gases emitted from agricultural lands – carbon dioxide, methane and nitrous oxide, says Chansheng 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. “Methane has a much greater warming potential than CO2, but at the same time, methane is very sensitive to management practices,” Li explained.

Draining the paddies stimulates root development in rice plants and accelerates the decomposition of organic matter in the soil to produce more inorganic nitrogen.

On the other hand, in waterlogged fields, methane is produced by soil microbes under anaerobic conditions – a process which is interrupted by midseason drainage of the paddies.

The researchers used satellite images, and a denitrification-decomposition model to calculate methane emissions from paddy fields in China.

The discovery is timely. Demand for rice in Asia is expected to increase by 70% over the next 30 years, and agriculture currently accounts for around 86% of total water consumption across the continent.

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