METHANE EMISSIONS FROM WETLAND RICE AREAS OF ASIA

Khalil and Rasmussen (1990) reviewed eleven global methane budgets published between 1978 through 1988. They found that methane emissions from rice paddies ranged from 18 to 280 Tg year-1 which correspond to between 10 and 70% of the total anthropogenic methane emissions. For this paper, we have reviewed and replicated three published techniques to estimate methane emissions from rice paddies. We present the results obtained and we propose to include soil characteristics to revise these estimates. Since 90% of rice production occurs in Asia, we have only focused our study on rice in Asia. The first technique we replicated, uses the Food and Agriculture Organization (FAO)'s country statistics and crop calendars to determine the land area under rice cultivation each month. Assuming a constant emission rate, Asian rice fields emit about 82 Tg methane year-1. The second technique we replicated, assumes that methane emissions represent a constant fraction of the net primary production and uses empirical relationships between net primary production and temperature and precipitation records. Asian rice fields then only produce 57 Tg methane year-1. The third technique we replicated, relates methane emissions to rice grain production. It involves the calculation of total organic matter added to rice paddy soils and assumes that a constant fraction is emitted as methane. This leads to an estimate of methane emissions from Asian rice fields of about 63 Tg year-1. We propose to use a classification of rice soils to categorize rice growing locations from potentially methane producing to non-methane producing areas. Using this distinction with any of die three methods we discussed, Asian rice fields emissions are reduced by about 25%.