Improved rice cultivation
Most of the world’s rice is grown in fields that are flooded year-round. When rice is harvested, most of the remaining plant material is left in the ponds, where it sinks to the bottom and begins to decay. Plants that decay in that low-oxygen environment generate methane gas.
Rice cultivation can be improved by alternately wetting and drying rice fields, or by draining flooded rice fields once during the mid-season. Such methods reduce the time that decaying plant material is submerged, thereby reducing methane emissions.
Improved rice cultivation could be applied to some 163 million hectares worldwide, an area roughly the size of Mongolia.
Improved rice cultivation would prevent the release of up to 159 million tonnes of carbon dioxide equivalent per year (MtCO2e/year). That’s comparable to the emissions from 34 million passenger vehicles per year.
In many Asian countries, farmers have little technical capacity to remove water from their fields during the rainy season.
More research is also needed to better understand the effect of water management on yield. Water management has been shown to increase yield in some cases and decrease yield in others, for reasons that are not yet clear. Continued research is needed to determine where and how water management can be most effectively implemented.
Currently, rice farmers have little incentive to improve their water management practices. Incentives such as subsidies might be necessary to improve rice production on a broader scale.
In a best-case scenario, water management of rice fields can reduce methane emissions by as much as 90 percent compared to full flooding. And field experiments show that the practice maintains, and in some cases improves, rice yields. Further, many of the world’s rice-producing regions have water shortages, making water management an attractive option for farmers.
In some regions, improved rice cultivation will be expensive to implement. But in others, it would be a relatively low-cost effort. In location such as India, the southern United States and parts of the Philippines, where farmers irrigate by pumping groundwater, the ability to engage in water management already exists. And doing so could save fuel costs related to operating the pumps. In areas with the technological capacity, improved rice cultivation could be implemented immediately.
Spotlight: Bohol Island, Philippines
The Philippines is among the world’s top 10 rice producing nations, and roughly 70 percent of the Philippine’s rice area is irrigated. By 2005, about one-quarter of rice farms in the Philippines used pump irrigation, making them good candidates for water management.
In 2005, the National Irrigation Administration constructed a new dam on the island of Bohol. The following year, the administration enacted an irrigation schedule for farmers drawing water from the dam.
As a result, many rice farmers in Bohol have switched to a system of alternate wetting and drying, which allows water levels to decline slightly below the soil before reflooding.
Thanks to the new system, farmers have been able to cultivate a larger area for rice production. In some parts of the island, farmers have been able to grow two crops each year instead of just one. Rice yields on Bohol have increased from 11 percent to 13 percent, though some of the increase might be attributed to other improvements in production.
Various water management approaches for rice cultivation are being used around the world. Alternate wetting and drying is being used in some regions of India, for example. And in China’s Sichuan Province, rice farmers have had success with a new technique that involves mulching paddies with plastic film, allowing farmers to draw down water levels during dry seasons.
- Adhya, T. K. et al. 2014. “Wetting and Drying: Reducing Greenhouse Gas Emissions and Saving Water from Rice Production.” Working Paper, Installment 8 of Creating a Sustainable Food Future. Washington, DC: World Resources Institute. Available online at http://www.worldresourcesreport.org.