稻田土壤中的CH_4产生

METHANE PRODUCTION IN RICE PADDY FIELDS

通过对意大利稻田及我国湖南地区稻田土壤中CH_4产生率的实地测量,甲烷产生主要发生在稻田土壤耕作层的还原层(2—20cm),但不同的农业操作对此有较大的影响;在意大利稻田中7—17cm土壤层是重要的甲烷产生区域,13cm处的CH_4产生率最大;由于我国湖南地区独特的有机肥铺施操作,土壤中甲烷的产生在土壤上部即耕作层氧化层以下(3—7cm)就达到最大值。土壤湿润度能影响土壤主要CH_4产生区域的深度,当土壤湿润度低于某个临界值后,主要的CH_4产生区域将向土壤深处移动,CH_4产生量也明显减少。种植水稻的稻田土壤中CH_4产生率要比不种水稻的大,同块稻田中CH_4产生率还有一定的空间变化。另外,水稻植物根部土壤比水稻行间土壤能产生较多的CH_4。在大多数情况下CH_4产生率在下午大于上午,但在一日间没有明显的日变化规律,因此CH_4排放路径的日变化可能是CH_4排放日变化的主要原因。在湖南地区不同施肥和水管理稻田的CH_4产生率差别十分显著。这种差别能完全在CH_4排放率的差异上体现出来。总有机酸含量差别在各不同施肥田中较小而在各不同水处理田中较大实验室培殖发现温度能够较大地影响土壤CH_4产生率,每上升10℃,甲烷产生率能增加3倍多。在整个水稻生长季节中。

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.