Characteristics Of N₂O Emission On Oil-sunlfower Field After Winter Wheat In Irrigation Area Of The Upper Yellow River

Nitrous oxide, as one of the third-most abundant greenhouse gas, has an important effect on theglobal warming and climate change. It comprises a smaller portion of greenhouse gas emissions.However, N₂O is estimated to have310and13.5times of the globlal warming potential per molecule ofC_O2and CH₄. N₂O atmospheric lifetime is approximately114years. Once released, it may linger in theatmosphere for decades. N₂O reduction efforts have the potential to mitigate climate change. It has beenconsidered to the important factor to cause globle warming. In addition to being one cause of climatechange and globle warming, N₂O is also an ozone-depleting substance. Through a series of reactions, itcan produce NO_x, ultimately lead to ozone depletion. N₂O has become one of the primary gases thatcause global climate change and ozone depletion. N₂O emission flux is high in Ningxia irrigation area.Due to its characteristics to endure alkali, drought and barrenness, Oil-sunflower has been an importantcrop that can improve soil fertility and increase the output in Ningxia irrigation area. Oil-sunflower isregard as the important economic crop and the common and widely planting pattern to grow multiplecropping oil-sunflower after winter wheat harvest. We can turn soil with straw manuring afterharvesting the seeds of oil-sunflower to improve soil fertility. And the yield of oil-sunflower will be100-150kg per mu after harvesting winter wheat to cultivate oil-sunflower. The research on greenhousegas emissions is less in this area, especially about N₂O emission in the oil-sunflower farmland croppingafter winter wheat harvest. Therefore, it has practical significance to study N₂O emissionscharacteristics under the main planting pattern to sustainable development in the irrigation area.The study on N₂O emission in oil-sunflower farmland under the long term fertilization treatmentswere carried out at Lingwu farm of Ningxia Hui Autonomous Retion. We studied N₂O flux and itsinfluencing factors in oil-sunflower farmland through fied observation and indoor soil column simulatedexperiments. In the first two years we grew rice and then to grow winter wheat from2009to2011.Different amount of fertilizer in the rice-wheat rotation farmland can form different soil fertility inoil-sunflower farmland. We studied oil-sunflower farmland that was no fertilizer application after winterwheat. N₂O emission was determined by using the static closed chamber-GC technique. We studied thedaily and seasonal dynamics of N₂O emission in oil-sunflower farmland and analysis the change in timeof N₂O flux in the long term of different fertilizer treatment conditions. And the effects of soil moisture,soil temperature, soil pH, inorganic nitrogen content and rain fall on N₂O flux have been analyzed.The main conclusions of this dissertation as follows:（1） There were great influences on N₂O emission fluxes in oil-sunflower growth period from theapplication of long term organic fertilizer and chemical nitrogen fertilizer. The treatment of addingorganic fertilizer were obvious above of that of only used chemical fertilizer （P<0.05）. And alltreatments were significantly above that of N0（no fertilizer treatment）. The average emission andseasonal emission flux of N₂O under different treatment （N300-OM, N240-1/2OM, N300, N240, N0）were significant. The average emission flux of N₂O were respectively44.82±17.70μg·m^-2·h^-1,47.58± 17.90μg·m^-2·h^-1,30.25±16.28μg·m^-2·h^-1,18.05±10.02μg·m^-2·h^-1,9.24±7.77μg·m^-2·h^-1, it showedthat N240-1/2OM＞N300-OM＞N300＞N240＞N0.（2） The season dynamic of N₂O flux did not change significantly during oil-sunflower growthperiod under the mutual influence of soil temperature, soil moisture, soil pH, inorganic nitrogen contentand rain fall. N₂O flux has a trend of changing from high to low in general during oil-sunflower growthperiod. In all treatments, N₂O emission fluxes were higher during the first month after oil-sunflowersowed. And the processing appeared the second peak in the end of August. During the first month, theaverage N₂O emission flux of the treatments N300-OM, N240-1/2OM, N300, N240, N0were116.51±33.16μg·m-2·h-1,113.92±37.25μg·m-2·h-1,97.09±25.23μg·m-2·h-1,60.75±10.06μg·m-2·h-1,21.06±22.82μg·m-2·h-1respectively, and the other stages N₂O average flux were20.93±6.27μg·m-2·h-1,25.47±7.96μg·m-2·h-1,7.98±17.95μg·m-2·h-1,3.81±13.10μg·m-2·h-1,5.3±15.06μg·m-2·h-1respectively.In the first month of oil-sunflower growth N₂O average emission fluxes were higher significantly thanother stages N₂O average emission fluxes （P<0.05）. N₂O flux decreased gradually with the soil nitrogenabsorbed and fall of temperature, and fluctuated in a much tighter range.（3） Daily dynamic of N₂O emission in the long term of different fertilizer treatment in theoil-sunflower fields did not show the obvious trend of day and night. However, daily dynamic of N₂Oemission fluxes were different obviously by the effects of fertilizer treatments. During seeding, therewere two peaks in11:00-13:00and18:00-22:00of N₂O daily dynamic in N300-OM treatment. Therewas a similar trend of N₂O flux change in N300and N0treatments. The trend had the single apex andappeared in the9:00. During anthesis, there were two peaks in11:00and22:00of N₂O daily dynamic inN300-OM treatment. There was a similar trend of N₂O flux change in N300and N0treatments. Thetrend had the multi-peaks, and appeared in the11:00,18:00and2:00.（4） There were different effects on N₂O flux among soil moisture, soil temperature, soil pH andinorganic nitrogen content on N₂O flux during different periods of oil-sunflower growth. The flux ofN₂O has significant positive correlation with soil moisture content （7.5%-46.8%） and has significantnegative correlation with soil pH （6.5-10.0）. Rainfall can cause N₂O emissions largely, and it often tookplace after the small rainfall or a period of time after rainfall. Rain infiltrate slowly during a short time.The surface of soil could store up some water. It could be found that the absorption of N₂O flux insoil-plant system. The soil was dry during the growth period of oil-sunflower. The soil moisture contentwas low, and it would influence the potential of N₂O flux determined by the temperature. Thecorrelation analysis between N₂O flux and soil inorganic nitrogen showed that N₂O flux of the treatmentN300-OM would increase with the improvement of ammonium nitrogen content. It was significant（P<0.05）. The other treatments had no obvious relationship with the content of ammonium nitrogen andthe same with soil nitrate nitrogen and N₂O flux. We analysised the influence of each factor on the N₂Oflux, the factors had interaction with N₂O flux. It showed that above5factors can explain52.5%changeof N₂O emissions flux during the oil-sunflower growth period.（5）The accumulations of N₂O emission rised as temperature increased, and they reducedgradually with the experiment time extended and reduce. They reached the lowest about7days later, almost close to0. The accumulation of N₂O emission had interaction with soil temperature andincubation time and the equation can be showed that Y=（-2.15T²+108.87T-1041.9）+[403.38ln（T）-984.36] ln（t）, T represents soil temperature and t represents incubation time.