Advances in Earth Science
• Articles •
Wang Mingxing Chen Dezhang and Shen Renxing
Shangguan Xingjian; Wang Mingxing Chen Dezhang and Shen Renxing. METHANE PRODUCTION IN RICE PADDY FIELDS[J]. Advances in Earth Science, 1993, 8(5): 1-12.
Experiments have been carried out to measure the CH4 production rates in the rice paddy fields in Hunan Province of China and in Italy. Methane production mainly occurs in the reduced layer(2-20cm)in the cultivated paddy soil,which may be largely influenced by different agricultural pratice. In Italy,7-17cm soil layer is the major methane producing area,with the maximum at 13cm. Because the organic manure is normally surface supplied to the field,maximum CH4 producing area is found in Hunan in the shallow cultivated soil region (3 -7cm) which is next to the oxic layer. Soil moisture may change the major depth where methane is dominantly produced. When soil moisture is lower than some value,not only the major CH4 producing area will "move" down but also less methane will be produced. The methane production rates in rice -planted field are larger than those in the un-planted field,and the difference increases with rice growing. Spatial variation of CH4 production rates is observed in the same field. Moreover ,methane production rates arc higher in the root soil than in the soil between rice plants. In most cases . CH4 production rate appears higher in the afternoon ,but with no obvious diurnal regularity. Therefore we think the variation of CH4 transport is the major factor that govern the diurnal variation of methane emission. The effect of different fertilizer and irrigation scheme on methane production is very obvious in Hunan.which is like that on emthane emission. The amount of total organic acid in different fertilized field appears almost the same but differs significantly in different water treated fields. Laboratory incubation shows that temperature may obviously affect methane production. When temperature increases by 10℃.methane production rates will triplie. In the rice growing season in Italy .methane production rates increase with the growing season and reach maximum in August before harvesting in the fields received no fertilizer or pure mineral fertilizer, and the same seasonal pattern also appears in the field received pure chemical fertilizer in Hunan. But in the fields received organic manure.there are two maxima of CH4 production rate .one at the beginning of rice growing, and the other before harvesting. In average.only 28%(Italy) and 16%(Hunan) of the produced methane emits to the atmosphere .while the rest is reoxided in the soil.