Rice is grown under a variety of climatic, soil and hydrological conditions in the world, from northeastern regions of China (53°N) to southern regions of Australia (35°S) and from sea level to altitudes of more than 2500m. It grows well in flood-prone areas of South and Southeast Asia (in as much as 5m of floodwater) and in drought-prone upland areas of Asia, South America and Africa (Neue and Sass, 1994). Nowadays, more than 90 per cent of the harvest area of rice is located in monsoon Asian countries and rice supports two thirds of the people living there as a staple food. In several Asian languages the words for food and rice, or for rice and agriculture, are the same, indicating its overwhelming importance for human survival over millennia.
In order to meet increasing demand for rice, the harvest area in the world has steadily expanded from 84 to 154 million hectares (Mha) between 1935 and 2005, corresponding to an annual increase of about 1 per cent (Figure 8.2). This rapid increase in the harvest area implies increased emissions of CH4 during the last 70 years. In addition, introducing high-yielding varieties, together with new cultivation technologies, has significantly increased rice
Source: Data from International Rice Research Institute (IRRI) World Rice Statistics yields, resulting in more than a threefold increase in world production during the last 50 years. It has been suggested that the increase in the yield has additionally increased CH4 emissions because of accelerating carbon turnover in the rice-soil system, caused by adding more organic matter to the soil in the form of crop residues (Kimura et al, 2004). The rate of global CH4 emissions from rice fields will probably increase further in the next decade, as there is an estimated global need for an additional 50 million tonnes of rough rice by 2015 (about 9 per cent of current production) in order to meet expected consumption rates (International Rice Research Institute, 2006).
Rice farming provides a livelihood to hundreds of millions of small farmers, challenged by the possibility of floods, droughts, pests and other threats to their crop. The major goal in their enterprise is to secure the crop yield necessary to sustain their families. Reducing CH4 emissions is of little concern to them in this situation. Nevertheless, a number of traditional management practices do curb CH4 emissions (although this is not their primary purpose), providing a 'win-win' outcome rather than a conflict between different economic, environmental and social goals. These issues are discussed in a later section.
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