| As one of the most impotant greenhouse gases, N2O has been paid great attention due to its substantial contribution to global warming and ozone depletion. Agricultural soil is a major source of anthropogenic N2O emission. With the adjustment of planting stucture, the area of vegetatable land has been increasing. Consquently, the research on monitoring N2O flux, understanding the pattern of N2O emission from vegetable soil as well as interperating key soil parameters is essential to exactly estimate the agriculture N2O emission at regional and even national scale. Furthermore, it also plays an important role on formulating the N2O inventory. In this study, outdoor pot experiments and laboratory incubations were conducted to study key soil parameters to nitrification, denitrification processes and N2O emission. A further investigation was to quantify the relationship between N2O emission and these soil parameters.Outdoor pot experiments were carried out in Nangjing Agricultual University during 2003/11-2004/03 (winter season) and 2004/03-2004/06 (spring season) to identify key soil parameters to N2O emission. Greengrocery was planted in growing season. Seven soil samples were collected from farmlands with a 10-year period of vegetable cultivation in Jiangsu and Shandong provinces. The local urea application was used at the rate of 150mg/kg as experiment treatments and the pots without fertilization as controls.To further explain the result of outdoor pot experiment with 7 vegetable soils conducted in 2003-2004 vegetable growing season, laboratory incubations were carried out for a period of 28 days using the C2H2 block technique to study the processes of N2O production. Fresh soil samples were collected from approximately 0-20cm depths of vegetable-cultivated fields in June 2004. In incubation experiments, 0.06% (V/V) C2H2 was used to inhibit soil nitrification and thus N2O was only released from denitrification in these soils with urea application. Many items such as the flux of nitrous oxide, soil organic carbon (SOC), total nitrogen (TN), pH, soil texture and mineralized nitrogen were measured.A significant variation in N2O emission was observed among soils whether the soils were fertilized or not in the winter season. Seasonal amount of N2O emission, ranging from137.4~218.7mg/m2 for the control, depended on soil parameters of pH, NH4+-N and NO3 -N. Urea application not only enhanced N2O emission but also enlarge the variation in seasonal N2O emission among soils, ranging from 319.9-1470.5mg/m . We compared N2O emission from vegetable soils in this study with that from wheat soils during 2000/11/08-2001/03/04 wheat-growing season. The amount of urea application in the vegetable soils was less than in the wheat soils (225 mg/kg), the N2O emission from the vegetable soils, however, had no obvious reduction. The average of N2O emission from vegetable and winter wheat soils was 14.9±8.2 and 17.4±8.1mg N2O-N /pot, respectively. Some key soil parameters including organic carbon, total nitrogen, C/N ratio, were identified to affect N2O emissions from the vegetable and the wheat soils when urea was applied.A significant variation in N2O emission was also observed among soils whether the soils were fertilized or not during the spring-growing season. The seasonal amount of N2O emission ranged from 123.6~205.4mg/m for the control in the spring season. Urea application only enhanced N2O emission and didn't enlarge the variation in seasonal N2O emission among soils, ranging from 380.7~860.9mg/m2. The variation was only observed in two groups of soils (Y6 and S1, X7 and S1). There were no pronounced relationships between N2O emissions of different soils and soil properties. N2O emission was strongly influenced by soil water content, which possibly concealed the effect of soil physico-chemical properties.There was a significant variation in N2O emission released from both soil nitrification and denitrification. Compared with denitrification, nitrification contributed greatly to N2O emission and deserved the amount of the total N2O...
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