Rice is the nutritious staple crop for more than half of the world’s people, but growing rice produces methane, a greenhouse gas more than 30 times as potent as carbon dioxide. Methane from rice contributes around 1.5 percent of total global greenhouse gas emissions, and could grow substantially. That may not sound like a lot, but agriculture as a whole contributes around one quarter of all emissions. Effectively tackling climate change could require cutting agricultural emissions by two-thirds even as we produce 70 percent more food, and rice will need to be part of that strategy.
From a purely technical standpoint, we know the basics of how to reduce rice-growing emissions dramatically, and these methods should also help conserve water and can boost yields. Rice grows mostly in flooded fields called rice paddies. The water blocks oxygen from penetrating the soil, creating ideal conditions for bacteria that emit methane. The longer the flooding lasts, the more those bacteria build up. Almost any farming method that reduces or interrupts the period of flooding can reduce methane.
A new WRI working paper discusses the options. They may include one mid-season “drawdown” of water to a level just reaching the roots, and it may include seeding rice in dried fields before flooding. Ideally, management includes a sequence of wetting and drying the paddies to prevent methane from building up. In Sichuan, China, many farmers don’t flood the rice plants at all, planting rice instead in a raised bed and flooding only the furrow. Doing any of these techniques has a potential to cut methane emissions in half. Combining dry seeding and one drawdown, or a perfect execution of a sequence of wetting and drying has the potential to reduce emissions by 90 percent.
In fact, Chinese and Japanese farmers typically drain their rice paddies once during the middle of the growing season because they have found it increases yields, and scientific studies have found yield gains elsewhere around the world. Less flooding also typically saves irrigation water, with less water percolating through the ground, running off or evaporating. Because rice-growing consumes 40 percent of all irrigation water, with water shortages in most major rice-growing regions, changes in management offer potential to conserve water.
Unfortunately, and despite the promise of these techniques, four case studies in the report identify many practical challenges, technical unknowns, and limited incentives that prevent most farmers from using them. One big issue is the ability to control water well enough to insure both wetting and drying. In the Philippines, farmers grow rice during a torrential rainy season that makes it impossible for them to drain their fields regularly. In the dry season, farmers there and in India often refuse to drain their fields because irrigation networks cannot guarantee new water will be available when needed. Even in California, with its sophisticated irrigation system, fields are too large and irrigation deliveries too slow to assure farmers that they can wet and dry their fields on cycle.
Moving forward therefore requires a detailed assessment, place by place, of where farmers have enough control over water to practice at least one form of water management. In India, farmers who pump groundwater should be able to employ these practices, and even in the wet season in the Philippines, farmers may be able to do one draining. Elsewhere, water management improvements might be needed. On Bohol Island in the Philippines, access to more reliable water from an improved irrigation dam came with a requirement to alternately wet and dry rice fields. The system has proved enormously successful for production and the environment.
Resolving scientific uncertainties is another step. Wetting and drying doesn't always increase rice yields, and some studies find it reduces them. Although adverse results probably reflect imperfect implementation, farmers are unlikely to embrace water management methods so long as uncertainty persists. Progress will require local and internationally coordinated studies to resolve uncertainties about yields and potential water savings.
Finally, farmers receive no reward for reducing emissions and suffer no penalty for increasing them. Although whole farming regions could benefit by saving water from reduced flooding, individual farmers often have no incentive to do so because they receive free water, or because subsidized electricity makes pumping water even from deep in the ground cheap.
Despite the potential advantages of improved water management, those opportunities will therefore mostly go to waste until governments shift incentives and support the work to get into the technical details place by place. This effort would require a few millions – not billions – of dollars. Governments have not committed these modest resources because mitigating agricultural greenhouse gases has been a low priority.
Rice management provides a great opportunity for the Global Alliance for Climate Smart Agriculture, newly formed by 18 countries and 53 other organizations. As an excellent start, its members could support the necessary technical analyses, and show through on-the-ground projects in the most promising locations how to tweak incentives and make improved water management a reality.