CH4 EMISSION FROM VARIOUS RICE FIELDS IN PR CHINA

The CH4 emission rates from Chinese rice fields have been measured in five typical areas representing all of the five major rice culture reg ions in People's Republic of China (P.R. China). Four types of diurnal variations (afternoon peak, night peak, afternoon-night double peaks and random pattern) of CH4 emission rates have been found. The first p attern was normally found in clear weather, the second and the third t ypes were only found occasionally in particular place, while the fourt h were found in cloudy or rainy weather. Due to the irregular pattern of the methane production observed in the morning-afternoon comparison experiment, the transport pathway influenced by certain factors, may be the major factor governing the diurnal variation of CH4 emission. S easonal variation patterns of CH4 emission differ slightly with differ ent field locations, where climate system, cropping system and other f actors are different. Two and three emission peaks were generally foun d during single and early rice vegetation periods, with the peak magni tude and time of appearance differing to small degree in individual si tes. A decreasing trend of seasonal variation was always observed in l ate rice season. A combination of seasonal change of transport efficie ncy and that of CH4 production rate in the paddy soil explains well th e CH4 emission. The role of rice plant in transporting CH4 varied over a large range in different rice growing stages. The reasons for inter nnual changes of CH4 flux are not yet clear. Great spatial variation o f the CH4 emission has been found, which can be attributed to the diff erences in soil type and soil properties, local climate condition, ric e species, fertilizer and water treatment. Experiments showed that whi le the application of some mineral fertilizers will reduce the CH4 emi ssion and CH4 production in the soil, the application of organic manur e will enhance CH4 emission and CH4 production in the soil. Any measur es which can get off easily decomposed carbon from organic manure may reduce C supply for CH4 production, and hence reduce CH4 emission. Fer mented sludges from biogas generators and farmyard-stored manure seem to be promising. In some parts of China, separate application of the o rganic and mineral manure instead of mixed application could be anothe r option. Frequent Scientific drainage and ridge cultivation, which ar e often used water management techniques in Chinese rice agriculture, have been proved in the experiments to be a very efficient mitigation measures to reduce CH4 emission from rice fields. By summarizing the p resent available data, China's rice fields contribute about 13.3 Tg yr (-1) (11.4-15.2) CH4 to the atmosphere. The total methane emission fro m global rice fields can be estimated 33-60 Tg yr(-1), much less than the estimates made before. If we extrapolate the measured data in Chin a with a consideration of measured data in other Asian country, the to tal global emission of CH4 from rice fields are estimated to be about 35-60 Tg yr(-1)