CH₄ EMISSION FROM A CHINESE RICE PADDY FIELD

CH4 emission rates have been measured continuously for the early rice of 1988 and late rices of 1987 and 1988 during entire growing seasons in a rice paddy field in Hangzhou,Zhejiang Province,China,by using an automatic sampling and analyzing system.During most parts of the seasons CH4 emission rates showed strong diurnal variations.Bi-mode patterns with the highest value in the afternoon and a second peak at mid-night were generally found for the early rice,while the highest values were almost always found in the night for the late rice.Bi-mode patterns with a second peak in the afternoon were also found during the reproductive phase of the late rice plants.These diurnal variations may be explained by the diurnal variations of the soil temperature and the activity of rice plants.Strong seasonal variations with one peak in the tillering stage and two during the reproductive phase of rice plants were observed for all the three growing seasons.The seasonal variations may be explained by the activity of rice plants,availability of organic substrates in the soil,and the activity of soil bacteria related to soil temperatures,Fertilization did not show significant effects on the total seasonal CH4 emissions but slightly changed the pattern of the seasonal variations of the CH4 emission rates.Averaged over the measuring periods and 8 spots,CH4 emission rates of 7.8 mg m-2 h-1 for the early rice and 28.6mg m-2 h-1 for the late rice were obtained.Based on these measured data,the total global emission of CH4 from rice paddies is estimated to be about 90 Tg/yr ranging from 70 to 110,accounting for 20% of the total source of CH4.