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To investigate the effect of different urea incorporation amount in different soils on N2O emission, a pot experiment was carried in 2002-2003. Four treatments were designed as the control (without urea incorporation); low N fertilizer level (334 kg/hm2); middle N fertilizer level (670 kg/hm); high N fertilizer level (1004 kg/hm2). In rice growing season, compared to control, the increment of N2O emission accumulation flux of each soil has no obviously differences among three N fertilizer levels. Contrarily, in wheat-planted soils, there are remarkably differences among three N fertilizer levels. Without urea incorporation, there are no differences among N2O accumulation emission flux of three soils. During the rice growing season, N2O accumulation emission flux of F soil (jiangsu province, lishui), G soil (jiangsu province, lianshui) and H soil (jiangsu province, agriculture academy) are 168, 127 and 146 mg/m2, respectively. N2O accumulation emission flux of F soil, G soil and H soil is 134, 124 and 168 mg/m2, respectively, during wheat growing season. Incorporation of urea into different soils yielded different influence on N2O emission. For example, at middle-N fertilizer, N2O accumulation emission flux from F soil, G soil and H soil is 976, 744 and 626 mg/m2, respectively. During rice-wheat rotation period, significance differences exists among N2O emission factors of three soils, with the value of (1.1 +/- 0.23)%, (0.75 +/- 0.17%) and (1.01 +/- 0.11)%. Furthermore, under the high N fertilizer level, N2O emission factors of three soils had no significantly difference (p = 0.3); while, the N2O emission factors existed difference among three soils under the low and middle N fertilizer level (F = 6.25, p = 0.01).

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.

Field experiment was conducted in 2001 rice growing season to understand the effect of organic manure application on CH4 and N2O emissions. Five treatments of fertilizer including urea and NH4HCO3 used as chemical fertilizer (CF), chemical fertilizer + pig manure (CF + PM), chemical fertilizer + cow manure (CF + CM), chemical fertilizer + rapeseed cake (CF + RC) and chemical fertilizer + wheat straw (CF + WS) were dedicated to this experiment. Results from the field observations indicated that application of the organic manure did not change the seasonal pattern of CH4 and N2O emissions but significantly affected the seasonal amounts. Seasonal amount of CH4 emission from the treatments of CF + CM, CF + RC and CF + WS was respectively 45%, 252% and 250% higher than that from the treatment of CF, but the application of pig manure (CF + PM) did not significantly influence the CH4 emission. The N2O emissions, on the other hand, were reduced by 18%, 21% and 18% for the treatments of CF + PM, CF + CM and CF + WS, respectively. Incorporation of rapeseed cake enhanced the N2O emission, yielding an increment of 22%. On a time scale of 20-year period, the integrated global warming potential (GWP) of CH4 + N2O released during the rice growing season for the treatments of CF + RC, CF + WS and CF + CM was respectively 154%, 136% and 17% higher than that for the CF treatment, while a reduction of 10% was obtained for the CF + PM treatment. The calculation of the GWP per unit rice grain yield suggested that the application of pig manure took the slight advantages not only in reducing the GWP but also in improving the grain yield.

To identify the key soil parameters influencing methane emission from rice paddies, and to quantitatively describe the relationship of methane emission with the soil properties, an outdoor pot experiment with a total of 18 paddy soils sampled from different regions in Jiangsu province was conducted in Nanjing Agricultural University during 2000 rice growing season. Seasonal average rate of CH4 emission for all the 18 soils was 6.42 +/- 2.70 mg.(m2.h)-1, ranging from 1.96 to 11.06 mg.(m2.h)-1, approximately a 5.6-fold difference between the maximum and the minimum. Correlation analysis indicated that the seasonal average of CH4 emission was positively dependent on soil sand content (r = 0.528, p = 0.024) and negatively on soil clay content (r = -0.484, p = 0.042). Negative correlation of CH4 emission against soil total nitrogen (r = -0.449, p = 0.062), available nitrogen (r = -0.611, p = 0.007) and NH4(+)-N(r = -0.649, p = 0.004) was also observed. Copper content of soils has a significant negative impact on CH4 emission. The correlation coefficient (r) of CH4 emission against soil available copper and with total copper was -0.594 (p = 0.009) and -0.547 (p = 0.019), respectively. No clear relationship existed between CH4 emission and soil carbon content. A further investigation suggests that the seasonal average rate of CH4 emission can be quantitatively determined by a linear combination of soil available copper, total manganese, and a ratio of available to total iron (R2 = 0.755, p = 0.0001).