| At present, the N-fertilizer use efficiency is still very low, about 30%-35%, while average loss rate is 45%. After application, the N-fertilizer is lost by ways of NH3 votilization, N2O emission, and nitrate leaching and so on. But researchers are not unanimous in the main ways of N-fertilizer losses and the total amounts of N2O emission. Some scientists indicated that the denitrification losses were ranged from a small quantity to 100 kgN2O-N/hm2, and about 30% N-fertilizer was lost through the denitrification. In this paper, field experiments were carried out to study the temporal and spatial variation, total amount, emission coefficient and main influential factors of N2O emission. The results are showed as follows:1. The results from the study of N2O emission during the maize season shows that significant temporal and spatial variations of the annual N2O amount were found in NPK+manure, NPK, N and CK treatments. The higher N2O emission took place in the July and August when both temperature and rainfall were high. The annual N2O emission amount among the four treatments decreased in the order: NPK+manure>NPK> N>CK treatments, the value of N2O fluxes were 15.5 kgN2O-N/hm2·a, 5.85 kgN2O-N/hm2·a, 2.97 kgN2O-N/hm2·a and 0.92 kgN2O-N/hm2·a, respectively. The diuranal change of N2O fluxes in NPK+manure; NPK and N treatments were significant. The N2O fluxes increased sharply from 7:00-14:00, then decreased gradually from 14:00-5:00. The N2O fluxes in NPK+manure; NPK and N treatments were highest during 13:00-14:00, the maximums were 810μgN2O-N/m2·h, 439μgN2O-N/m2·h and 144μgN2O-N/m2·h, respectively, while they were lowest during 1:00-2:00, the minimums were 137μgN2O-N/m2·h, 47μgN2O-N/m2·h and 32μgN2O-N/m2·h. The amounts of N2O-N losses in NPK+manure; NPK and N treatments account for 1.45%, 0.86% and 0.36% of total applied N, respectively.2. Under winter wheat/summer maize rotation system, the spatial variation of N2O concentration in the sandy soil was significant. The highest N2O concentration occurred in 140 cm soil layer while the lowest in 15 cm soil layer. N2O concentration in soil profiles decreased in the order: 140 cm>100 cm>60 cm>30 cm>15 cm. For the temporal variation, N2O concentration in every soil profile during the maize growing season was higher than the wheat season. A great temporal variation was found during a year. The highest N2O concentration took place in the July and August with the high temperature and rainfall. N-fertilization increased the N2O production in the soil profile significantly. The N2O concentrations in each soil layer were higher in fertilized treatment than that in the CK treatment and it was 1.37, 1.62, 1,21, 1.37 and 1.27 times than that in the related soil layer in the CK treatment. However, they had the same temporal and spatial variations trends both in N and CK treatment. Furthermore, the soil active organic carbon in the soil profiles of the different terrace in Weihe River from 0 to 200 cm was measured. The results showed that the active organic carbon content in 0-20 cm soil layer was highest and it decreased in the order: the third terrace>the second terrace>the first terrace>the beach. The soil active organic carbon in every terrace decreased significantly along with the increase of the soil depth but it varied insignificantly from 60 cm to 200 cm. The average soil active organic carbon content in 60-200 cm in the third terrace, the second terrace, the first terrace and the beach was 1.10 g/kg, 1.15 g/kg, 0.64 g/kg, 0.26 g/kg, respectively, which indicated that the deep soil layer still could offer the active organic matter for the activity of microorganisms.3. the N2O fluxes in the cabbage, cauliflower and cucumber treatments decreased in the order: cabbage>cucumber>cauliflower. N2O fluxes from the open vegetable field showed a significant positive correlation with the soil temperature. During the entire growth periods of cabbage, cauliflower and cucumber, the amounts of N2O emission were 1.52 kgN2O-N/hm2, 0.97 kgN2O-N/hm2, 0.97 kgN2O-N/hm2,accounting for 0.43%, 0.28%, 0.73% of total applied N, respectively. The N2O fluxes from both cucumber and tomato field in greenhouses were highest during 13:00-14:00, the maximum N2O fluxes were 230.6μgN2O-N/m2·h and 97.5μgN2O-N/m2·h, respectively. There existed a valley of N2O emission in both greenhouses (63.6μgN2O-N/m2·h and 11.6μgN2O-N/m2·h, respectively) during 23:00-0:00. The N2O fluxes from the rows were higher than that from the inter-rows in the greenhouses. The total amount of N2O emission was 2.40 kgN2O-N/hm2 during the tomato growing season in the greenhouse.
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