Advances in Earth Science
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Shangguan Xingjian,Wang Mingxing and Shen Renxing
Shangguan Xingjian,Wang Mingxing and Shen Renxing. REGULARITY OF METHANE EMISSION FROM RICE PADDY FIELDS[J]. Advances in Earth Science, 1993, 8(5): 23-36.
CH4 emission rates from rice paddy fields have been measured in the past several years over the three main rice culture regions in China, which are middle and lower reaches of Changjiang River, southwest region and middle China region. The regularity and characteristics of CH4 emission are described in this paper. Three types of diurnal variation of methane emission have been observed, which are afternoon - maximum mode, night -maximum mode and two-peak mode with maxima occured both in the afternoon and at night. The diurnal variation of CH4 transport efficiency causes these three types of diurnal variation pattern. Different variety of rice plant and weather condition may change the diurnal variation of CH4 transport ,hence affecting the diurnal variation pattern of CH4 emission. With the growing of rice plants. the varying range of diurnal CH4 emission rates also changes.The seasonal pattern of CH4 emission rates from rice paddies for early rice is different from that of late rice. For early rice, CH4 emission normally shows three maxima. The first and the third are caused by high CH4 production rates in the paddy soil, and the second is caused by high CH4 transport efficiency. For late rice. CH4 emission appears highest shortly after rice is transplanted, and then decreases gradually with rice growing. The seasonal variation pattern of CH4 emission of single rice in Sichuan province is similar to that of early rice, but without the first peak. Different trend of air temperature can explain the difference in seasonal pattern of methane emission for early and late rice . The status of flooded water may also greatly affect the seasonal variation of methane emission.The fertilizer containing SO42- may reduce CH4, emission, but its effect depends on the amount of organic matter in the soil. The use of urea and KCl may also lower CH4 emission. But its reduction effect is smaller than the positive enhencement by organic manure, which indicates the great importance of organic fertilizer. The fermented manure from bio gas pits which has been stored up in the open air may largely reduce methane emission. Different fertilizer treatment can also change temperature effect of CH4 emission.Different irrigation method has great influence on CH4 emission. Deep water cover reduces CH4 emission for early rice, while the opposite is ture for late rice. A 3 - day - interval frequent drainage dose not affect CH4 emission too much for the whole growing season. The CH4 emission rate from the field received constant moisture is very low for both early and late rice.Interannual variation of CH4 emission in all the three regions has been observed. The mean emission rate in middle and lower reaches of Changjiang River is 0. 39mg · m -2·d-1 and 0. 75mg · m-2 · d-1 for early and late rice respectively, while in middle China region it is 0. 28mg · m-2 · d-1 and 0. 41mg · m-2 · d-1 respectively, and for the single rice growing region in Sichuan it is 1. 41mg · m-2 · d-1.