Rice cultivation can aggravate global warming: Study

Wednesday, 24 October 2012 01:08 - - {{hitsCtrl.values.hits}}

Washington: Rising temperatures and high levels of carbon dioxide in the atmosphere are causing rice paddies to release more of the potent greenhouse gas methane, a new research has claimed.

Researchers from the Trinity College Dublin, Northern Arizona University and University of California in Davis gathered all published research to date from 63 different experiments on rice paddies, mostly from Asia and North America.

“Our results show that rice agriculture becomes less climate friendly as our atmosphere continues to change. This is important, because rice paddies are one of the largest human sources of methane, and rice is the world’s second-most produced staple crop,” Dr. Kees Jan van Groenigen, lead author of the study said, in a statement.

Groenigen and colleagues used a technique called meta-analysis, a statistical tool for finding general patterns in a large body of experimental data.

“Two strong patterns emerged when we analysed all the data: first, more CO2 boosted the emissions of methane from rice paddies, and second, higher temperatures caused a decline in rice yields,” said Professor Bruce Hungate of Northern Arizona University and co-author of the study.

Methane in rice paddies is produced by microscopic organisms that respire CO2, like humans respire oxygen. More CO2 in the atmosphere makes rice plants grow faster, and the extra plant growth supplies soil microorganisms with extra energy, pumping up their metabolism.

Increasing CO2 levels will also boost rice yields, but to a smaller extent than methane emissions. As a result, the amount of methane emitted per kilogramme of rice yield will increase.

Rising temperatures were found to have only small effects on methane emissions, but because they decrease the rice yield, they also increase the amount of methane emitted per kilogramme of rice.

“Together, higher CO2 concentrations and warmer temperatures predicted for the end of this century will about double the amount of CH4 emitted per kilogramme of rice produced,” said Professor Chris van Kessel of the University of California in Davis and co-author of the study.

“Because global demand for rice will increase further with a growing world population, our results suggest that without additional measures, the total CH4 emissions from rice agriculture will strongly increase,” Kessel added.

However, the authors point out that there are several options available to reduce methane emissions from rice agriculture. For instance, management practices such as mid-season drainage and using alternative fertilisers have been shown to reduce methane emissions from rice paddies.