1. Cultivation of Rice

Rice cultivation which feeds a vast proportion of the people of the tropical world gives rise to large quantities of Methane gas. When rice fields are flooded with water and treated with artificial fertilizer the flooding cuts off the oxygen supply to the soil, causing the organic matter to decompose into Methane gas.
Modern perennial irrigation is highly productive and makes three crops a year quite feasible. About 11 percent of the world's crop land (250 million hectares in 1994) are under perennial irrigation and supply as much as 40 percent of the world's food. [i] But can we compromise our food habits and consume food which leads to lesser GHG emission? Is consumption of rice necessary? If cultivation of rice is so important can we develop the kind of rice variety which emits less? Is there a method of cultivation which could enhance productivity and reduce the emission? Some studies suggest this is possible.

• Emissions during the growing season can be reduced by various practices (Yagi et al., 1997; Wassmann et al., 2000; Aulakh et al., 2001). For example, draining wetland rice once or several times during the growing season reduces CH4 emissions (Smith and Conen, 2004; Yan et al., 2003; Khalil and Shearer, 2006). This benefit, however, may be partly offset by increased N2O emissions (Akiyama et al., 2005), and the practice may be constrained by water supply.
• Rice cultivated with low exudation rates could offer an important methane mitigation option (Aulakh et al., 2001).
• In the off-rice season, methane emissions can be reduced by improved water management, especially by keeping the soil as dry as possible and avoiding water-logging (Cai et al., 2000, 2003; Kang et al., 2002; Xu et al., 2003).
• Increasing rice productivity can also enhance soil organic carbon stocks (Pan et al., 2006).
• Methane emissions can be reduced by adjusting the timing of organic residue additions (e.g., incorporating organic materials in the dry period rather than in flooded periods; Xu et al., 2000; Cai and Xu, 2004), by composting the residues before incorporation, or by producing biogas for use as fuel for energy production (Wang and Shangguan, 1996; Wassmann et al., 2000). [ii]