Around the world, most rice is grown in paddy fields, which are flooded with water throughout the growing season. While a rice field is flooded, the soil is in an anaerobic (oxygen-free) environment. This allows microbes to produce methane, an important greenhouse gas, as they ferment organic matter in the soil.
A key method of reducing methane emissions from rice cultivation is to reduce the amount of time the rice fields remain flooded. Draining a field halfway through the growing season or engaging in alternating wetting-and-drying (AWD) greatly reduce methane emissions, and these practices may either decrease or increase crop yields, depending on the soil conditions, climate conditions, and rice cultivar. However, these water management practices may not be possible in some areas that are naturally flooded, where farmers lack reliable control over irrigation systems, or where fields are not sufficiently level (due to the formation of wet and dry pockets).
In areas where reduced flooding can increase rice yields, programs to educate farmers in good water management practices (including demonstration projects) can be helpful. Some governments subsidize the cost of water or electricity used for pumping water to farmers; these subsidies reduce the incentive for water conservation. Increasing the price of water or of electricity used to pump water by ending these subsidies or applying taxes can encourage adoption of better water management practices, which can reduce methane emissions. Finally, in areas where scarce water is allocated by allotment to different farmers, those farmers who use water more efficiently can be rewarded with larger water allotments.
Reducing the amount of organic matter that is added to rice paddies as fertilizer (such as detritus from the last harvest’s rice plants and manure) reduces methane production, as do slow-release forms of fertilizer and the use of nitrification inhibitors (discussed in the cropland management section).