N₂O Emission And Estimation Under Different Land Types

As one of the most important greenhouse gases, N₂O has been paid great attention due to its substantial contribution to global warming and ozone depletion. Different land use can cause corresponding changes in soil N₂O emission flux, density and vertical distribution. There is obvious difference in land use type and farmland management since 1980s, so the study on N₂O flux of different soil types, flux regulation and affecting factors plays an important role in evaluating of farmland N₂O flux, making flux lists and improving land use structure.In order to study the different soil N₂O flux characters and their affecting factors in Shaanxi Province, we committed a raise experiment and analyzed three factors--soil depth, moisture and temperature which can affect the N₂O flux mechanism. The results indicated:1. N₂O emited from undisturbed soil samples of forest soil (Loessial soil) produced mainly in the depth of about 10 cm, and N₂O emissions from the destruction of mixed soil is in the depth of 5cm around, under the depth of 10 cm, 15cm and 20cm, N₂O emissions of undisturbed soil is significantly higher than the average mixed soil samples. The forest soil of ZiWuling area in northern Shaanxi province is the source of N₂O emission.2. The average amount of N₂O emissions of undisturbed soil, under the grass soil (Loessial soil) is significantly higher than mixture. N₂O emissions of the mixed grass soil and undisturbed soil samples are at the largest in depth of 10.3 cm, 2.4cm separately, and N₂O emissions in the depth of 0-5cm is largest of grassland in the northern of Shaanxi province.3. The N₂O accumulative emission of farmland soil is much higher than the fallow land in the northern Shaanxi province significantly, especially in the depth of 5^-25cm. And the N₂O emission flux of farmland is twice of fallow land in northern Shaanxi province.The change scope of N₂O emission flux under farmland, forest and grass is separately in 0.1～24.58μg·m^-2·h^-1,-0.17～12.36μg·m^-2·h^-1,-0.21～12.02μg·m^-2·h^-1. And the maximum of N₂O emission flux under the farmland is higher than the forest and the lawn obviously, approximately 2 times for the forest land and lawn. It maybe attributed to the usage of chemical fertilizer.4. Under various moisture contents, N₂O emission of the Lou soil obviously is higher than loessial soil, and under same moisture contents, N₂O emission of the Lou soil is higher than loessial soil also. Two kinds of soil N₂O emissions exists obvious temperature effect, moisture content effect and nearly approximate nitrogen nutrient effect.5. Annual average N₂O emissions of farmland, grassland, and the forest soil in Shanxi province respectively is 2.71kg·hm^-2·a^-1,0.293kg·hm^-2·a^-1,0.296kg·hm^-2·a^-1. Then the annual average of N₂O flux in farmland obvious is higher than the forest soil and grassland. The annual total N₂O flux decreased in the order:: Farmland> forest soil > grassland.Forest area in Shanxi province approximately is 2.5 times of farmland's, however because of high average emission flux, annual total N₂O flux of forest soil was still smaller than the farmland. Therefore conversion of cropland to forest and grassland may reduce the N₂O emissions, and it is vital significance to alleviate global warming.