| Even though nitrous oxide loess is negligible for the nitrogen losses, it has significant impact for the whole eco-agriculture system. Cause the limited development of in site method for measuring N2O, it is still a hot and tough area for nitrogen research. Since more and more attention had been put on the environment nowadays, there are a lot of work had been done such as in-site measuring methods, emission amount and influential factors in the whole world. However, there isn't any work had been on loess soil about it. In this paper, filed experiments and incubation test have been combined together to study the where, when N2O produced in different layers of soil and NiO emissions on the soil surface under wheat-corn system. In addition, by using soil probes method, closed chamber method and C2H2 inhibition intact soil core method the realtionship between N20 emission and water, nitrogen, carbon concentration as well as long-term different fertlization had been studied. The results are shows as follows:1.There is denitrification exsited in loess soil. Significant spatial variation and temporal variation of the nitrous oxide amount were found in the soil. Soil N2O concentrations were high in the year with high rainfall as well as corn growing season. The temporal variation was correlated with the water supply (such as rainfall or irrigation), and N2O peaks were occurred 3 days after water events. Both the control and fertilized plots have the same trend. Meanwhile N2O spatial variation in the profile of control plot followed the order: 60cm = 90cm == 150cm > 30cm > 10cm, while those in the fertlized plot as the order: 60cm, > 90cm = 150cm > 30cm > 10cm. The denitrification of 60 ~ 90 cm soil layers are the main N2O losess in soil profiles of loess soil.2. There are two N2O emission peaks exsited during the whole year, one is from June to August in summer when the temperature is 'higher and another one is from January to Feberue in winter when soil in freezing-thawing cycle under the corn-wheat growing sytsem. N2O flux is higher during corn growing season than wheat. Among all treatments N2O fluxes changes in the order as: chemical NPK + manure > chemical NPK. > amonia nitrogen > nitriate nitrogen. N2O flux is about 0.8-1.5 kgN2O-Nhm-2 .a-1 without fertilizeration at all.3. Both the denitrification amounts and N2O emissions have high spatial variations. The variation of denitrification amounts is higher than N2O emission, fertilized plot is higher than control polt. The variation is the combination all water, NO3-, temperature and so on. Carbon was the limited factor that controled denitrification in the soil. When carbon was supplied, nitrate content and water became the limited factors.4. The denitrification losses increased with the available carbon concentration increasedfor both of the arable field and peddy soil field of loess soil under the suitable nitrate nitrogen concentration and mositure content. Whereas the denitrificaion losses decreased with the NOs "concent reach a certain level under the suitable available carbon and water content. However, when we used nitrite nitrogen as the nitrogen sources, the denitrification loess raised with the NO2" concentration increased.5. At both 90% water hold capicity (abrrevinsion WHC) and 70% WHC water content, N2O fluxes from the ammonium plots were higher than nitrate plots. Soil water status had little influence on the N2O fluxes fron ammonium plot, while it had a bigger effect on the nitrate plots under the experimental condiation. Meanwhile, soil temperature, pH, soil water content had certain influences on N2O emissions.6. N2O emission in the dry land usually is low but it will increase rapidly after irrigated the land or rainfall, the trend of N2O concentration in the soil profiles and N2O emission flux changes with the time were similar to that temporal rainfall variation pattern. When soils have same WFPS content, the influence on N2O emission of soil from wetting to drying cycle is bigger than that from drying to wetting. For the form...
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