[Impact of different levels of nitrogen fertilizer on CH4 emission from different paddy soils]

To investigate the effect of different urea incorporation amount in different soils on CH4 emission, a pot experiment was carried in 2002. Four treatments were designed as the control (without urea incorporation); low N fertilizer level (0.64 g urea/pot); middle N fertilizer level (1.28 g urea/pot); high N fertilizer level (1.93 g urea/pot). During rice growing season, incorporation of urea into different soils yielded different influence on CH4 emission. Without urea incorporation, significance differences existed among CH4 emission flux of three soils, with the values of 6.7 g/m2, 12.6 g/m2 and 8.3 g/m2, respectively. Incorporation of urea reduced considerably CH4 emission of three soils. A further investigation indicate that CH4 emission of three soils largely decreased and three soils NH4(+)-N content obviously increased from low N fertilizer level to middle N fertilizer level. It concluded that soil NH4(+)-N content is a key influence factor on CH4 emission after incorporation of urea into soils. From middle N level to high N level, CH4 emision of soil G (Lianshui, Jiangsu) and H (Jiangsu Academy of agricultural sciences) reduced, while CH4 emission of soil F (Lishui, Jiangsu) had no obvious significance with the value of 3.0 g/m2 and 3.4 g/m2.