| It is well known that rice field soils are the major sources of atmospheric methane and nitrous oxide (NO2). Since China is the largest producer of rice grain, the contribution of trace gas emissions from rice field soils to the greenhouse effects have become the focus of researches both in agriculture and environment. With the limitation of water resource, worldwide, a number of studies have been conducted in rice planting in aerobic condition, in which the ground cover rice production in aerobic condition is a novel cultivation technique. The characteristics of trace gas fluxes from rice field soils are accordingly changed in aerobic condition compared with those in waterlogged condition.Field experiments were carried out to assess CH4 and N2O emission rate in such two different cultivation systems of rice as traditional waterlogged production and aerobic production with different covers during rice-growing seasons in 2001 and 2002. The experimental field was selected in the suburb of Yancheng city of Jiangsu Province, located at latitude 33 27'N, longitude 120 11 E. The total rainfall during rice-growing season was 484.2 mm in 2001 and 440 mm in 2002. The soil (Halaquepts) had 12.5 g kg-1 of organic matter, 0.8 g kg-1 of total nitrogen and 8.3 of pH in the cultivated layer.There were four treatments, i.e., three treatments designed in aerobic rice production system such as the plots covered with plastic film (F), mulched with crop straw (M) andbare (without any cover)(B) and one treatment in waterlogged rice production (W)(as CK)in 2001. The bare treatment was replaced by the treatment covered with straw mulch using recommendation fertlization(R) in the second trial season (2002), for the results of 2001 showed many advantages of the straw mulching treatment, i.e., saving labour and costs, low-pollution and high yield.The total N2O fluxes in aerobic condition were five to six times higher than those in waterlogged soil, while the total emissions of CH4 in waterlogged soil were eight tonineteen times higher than those in aerobic condition during the rice growing period in 2001. There was no significant difference in the emission rates of methane and nitrous oxide in aerobic condition with traditional fertilization. The methane emission rates during the growing period in waterlogged condition were closely related to the different growing stages. The maximum emission rate of CH4(5.0 mg CR4 m~2 h-1) from waterlogged soil was found in the tillering stage of the rice crop in 2001. Fertilization was the primary factor affecting the N2O emissions in aerobic condition. A peak of the nitrous oxide emission rate was observed after each fertilization during the rice growing stages of all treatments in aerobic condition. Because of no basal fertilization in the treatment R, the total N2O fluxes of this treatment during the entire cultivation period was equal to that in waterlogged condition.In 2001, the rice grain yield of the treatment W was higher than that of the treatments in aerobic condition, while there was no significant difference of the rice grain yield among the treatments in aerobic condition on the significant level of 5%. There was no significant difference of the rice grain yield in 2002 between the different treatments except that the yields of treatment R and F were significantly lower than that of treatment W.In a 20-year time domain, there was no significant difference between the global warming potentials of the three treatments in aerobic condition and that of the treatment W based on the calculation of both N2O and CH4 emissions in the different treatments. But for the long-term period of 500-year, the greenhouse effect would be aggravated by the increased N2O emission from rice field soil in aerobic condition. Calculation of the total global warming potential for these two gases indicated that treatment R would be a preferable fertilization management to mitigate greenhouse gases emission either for the short or for the long-term period.The methane emission rate from ri...
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