| Global warming and ozone depletion are two global environmental issues. Nitrous oxide (N2O) is a trace gas responsible for global warming and depletion of ozone. It is no doubt that the agricultural soil plays an important role in the global budget of atmospheric nitrous oxide. Therefore, this study was carried out in Three Gorges Reservoir Area. We examined soil N2O fluxes and the relationship obtained by environmental factors in different land use types of upland transferred from paddy, upland, orchard, vegetable field and woodland. The primary objective was to explore the effect of different land uses on dissolved organic carbon, dissolved organic nitrogen, microbial biomass carbon and microbial biomass nitrogen, which in turn, caused to shift in N2O flux, and to examine that soil moisture interact with dissolved organic carbon, dissolved organic nitrogen, microbial biomass carbon and microbial biomass nitrogen to control the N2O flux. We also carried out incubation and field experiments to research the effect of atmosphere nitrogen deposition and the external source carbon and nitrogen incorporation on N2O emission. The results of this study are presented as follows:1. The mean annual budget of N2O emissions from different land uses was followed this relationship:vegetable field> upland transferred from paddy> orchard> upland> woodland, being 4.01,2.39,2.20,0.62 and 0.15 kg·hm-2·a-1, respectively. Land use types had a great effect on N2O fluxes, which were significantly correlated with the amount of nitrogen fertilizer applied. The research showed that nitrogen fertility can increase the N2O emissions from soils.2. Significant seasonal differences of N2O fluxes were observed from all across the years and land uses. Soil N2O fluxes were significantly higher in hot-humid season as compared to cool-dry season, as was approximately consistent with the changes of air and soil temperature.3. Soil N2O fluxes were significantly correlated to soil NO3-N contents in all land use types, the correlation coefficient R2 of 010-0.74 (P<0.05). While a significant influence of soil NH4+-N on the soil N2O flux was observed for vegetable field and woodland only. NO3-N greater effect on N2O flux as compared to NH4+-N.4. A highly significant positive correlation existed between N2O fluxes and soil dissolved organic carbon for upland and woodland. Which indicated that soil dissolved organic carbon ultimately controls the magnitude of N2O emissions in upland and woodland. Soil N2O emissions were positively correlated with CO2 emissions in orchard and woodland. 5. Significant differences in soil microbial biomass carbon, microbial biomass nitrogen, dissolved organic nitrogen and microbial quotient among different land use types, being higher from vegetable field, orchard and upland transferred from paddy than in woodland. Soil dissolved organic carbon, dissolved organic nitrogen, microbial biomass carbon, microbial biomass nitrogen and microbial quotient were significantly higher in vegetable field, orchard and upland transferred from paddy with respect to other land use types, therefore, maximum N2O emissions were observed from this three land use types. And soil dissolved organic nitrogen, microbial biomass carbon, microbial biomass nitrogen and microbial quotient were lowest from woodland, consequently, the lowest N2O flux was observed in woodland. N2O fluxes were significantly correlated to soil microbial biomass carbon and dissolved organic nitrogen from woodland as little human disturbance. And a slight influence of microbial quotient on the N2O flux was found for woodland.6. The results showed atmosphere nitrogen deposition have great effect on N2O fluxes only upland and woodland among different land use types. Cumulative N2O emissions from woodland soil which accounts for 0.61%～1.4% of atmosphere nitrogen deposition. Nitrogen deposition had significant effect on N2O emission, as nitrogen deposition could enhance the soil microbial biomass carbon, microbial biomass nitrogen and NO3-N contents.7. The significant influence of extrinsic carbon, nitrogen (plant residue) application on soil N2O emission, N2O fluxes from five plant residue treatments were significantly higher than without plant residue treatment. The season cumulative N2O emission of without plant residue treatment was 0.55 kg-hm-2, while season cumulative N2O emissions of plant residue treatments were 1.05 to 3.02 kg-hm-2. Significant negative relationship was found when cumulative N2O emissions were logarithmically regressed with C:N ratio across crop residue treatments. Lower C:N ratio of plant residue provided microbial biomass carbon and dissolved organic carbon contents, hence resulted in higher N2O emissions. Plant residue C:N ratio might play an important role in N2O production and emission. In order to get control on N2O emission from the field, proper management practices needs to be implemented.8. The result of laboratory incubation showed that N2O fluxes from yellow brown soil and purple soil significantly differed among different treatments with different fertilizer under two soil water contents. Synthetic N fertilizer and synthetic N fertilizer plus organic material both stimulated N2O fluxes under higher water contents from yellow brown soil. Synthetic N fertilizer did not significantly effect on N2O flux, while synthetic N fertilizer plus organic material markedly enhanced N2O flux under lower water content from yellow brown soil. All fertilizer treatments increased N2O flux from purple soil, except lower synthetic N fertilizer plus organic material under higher soil content. Cumulative N2O emission was relate to the change in dissolved organic carbon, and a positive relationship between the cumulative N2O emission and the consumed dissolved organic carbon was observed. Soil dissolved organic carbon and dissolved organic nitrogen had significant influence on N2O emission. Additionaly, The relationship between N2O fluxes and soil dissolved organic carbon contents had dependence on soil moisture.The study showed that there was significant difference in N2O emission between different land uses, which was subjected to control of nitrogen fertilizer applied. Soil dissolved organic carbon, dissolved organic nitrogen, microbial biomass carbon, microbial biomass nitrogen and microbial quotient were significantly higher in vegetable field, orchard and upland transferred from paddy due to more nitrogen fertilizer applied, therefore, maximum N2O emissions were observed from these land use types. The residue type was thought to be an important factor affecting N2O emission. Lower C:N ratio of plant residue provided greater microbial biomass carbon and dissolved organic carbon contents, hence resulted in higher N2O emissions. To meet the improve soil fertility and mitigate global greenhouse gas, the current findings indicate that reduce consumption of synthetic fertilizer nitrogen and select suitable crop residue may be preferred strategy.
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