| A field experiment for two years (2005．06～2006．10) was carried out to measure CH4 emission flux from paddy fields of rice-winter wheat rotations in situ using the manual closed static chamber-gas chromatography method in Kunshan Experiment Base of Drainage and Irrigation, Suzhou City, Jiangsu Province. Based on mathematical statistical methods, this study systematically and thoroughly analyzed the effects of controlled irrigation on regularity of methane emission from paddy fields and its influence mechanism taking continuous flooding irrigation pattern as the comparison. The results of this study are presented as follows:1,The seasonal average CH4 flux from paddy fields under controlled irrigation (PFCI) varied from 0．8mg·m-2·h-1 to 8．15mg·m-2·h-1 , and the total CH4 emission from 2．4g·m-2 to 24．5g·m-2 , reduced by 39%～85% compared with that from paddy fields under flooding irrigation (PFFI).2,The seasonal variation of CH4 emission from PFCI appeared distinct one-peak model. The peak flux was observed at the initial and peak tillering stages of rice, more than 10 days earlier than that from PFFI. The diurnal variation of CH4 emission from PFCI appeared regular single afternoon-peak model.3,The seasonal model of CH4 flux from PFCI was mainly regulated by drainage at the initial tillering period of the rice or the receding water-layer, while the magnitude of CH4 flux peaks depended on whether organic manure was incorporated into the field before transplanting. Moreover, the soil water status close to saturated water content was also conducive to reduce CH4 emission from PFCI.4,Regardless of irrigation pattern, the changes of both air temperature and soil temperature were the important reason for seasonal and diurnal variation of CH4 emission from paddy fields. When soil Eh value was over 100mV both the seasonal and diurnal CH4 flux from PFCI decreased exponentially or linearly with the increase in soil Eh value.5,Dissolved CH4 concentration in soil solution varied from 0．01 to 7．76umol·L-1 in PFCI,and from 0．02 to 24．99umol·L-1 in PFFI. The former was obviously lower than latter. Additionally, to a large extent, CH4 flux from PFCI could be determined by dissolved CH4 in soil solution at 20cm depth.6,Irrespective of irrigation pattern, CH4 flux was not prominently affected by the variation of tiller numbers and plant height. When CH4 release was suppressed due to the implement of no water layer under controlled irrigation, stronger root activity of the rice would display to stimulate CH4 emission.7,For comparison with flooding irrigation, rice controlled irrigation pattern could save irrigation water use 75%～80%, maintain even increase grain yield, and reduce CH4 emission from paddy fields largely. It could realize the harmonious unification among CH4-reducing, water-saving and production-increasing.Firstly, in conclusion, the receding water-layer and practical irrigation of controlled irrigation pattern, especially at the initial tillering period of the rice, is vital important to affect CH4 release from paddy fields. Secondly, to a large extent, CH4 flux from PFCI could be determined by dissolved CH4 concentration in soil solution at 20cm depth, and the seasonal variation of CH4 emission from PFCI maybe derived from that of dissolved CH4 in soil solution. Thirdly, rice controlled irrigation pattern could realize the harmonious unification among CH4-reducing, water-saving and production-increasing, and would be one of most promising strategies to mitigate CH4 emission from paddy fields.
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