Characteristics And Influencing Factors Of N₂O Emission From Winter Wheat Field Under Different Tillage And Nitrogen Application Conditions

Greenhouse gases have always been a hot issue of global concern,and agricultural activities are an important source of greenhouse gas N₂O emissions.In order to explore the characteristics of N₂O emissions from winter wheat fields in the Loess Plateau under different farming methods and nitrogen levels,the dynamic changes of N₂O emissions from rain-fed winter wheat fields during the entire growth period were studied by static box-gas chromatography.In this study,winter wheat’Xiaoyan22’was used as the material,and a two-factor split area design was adopted.The main area was 3 farming modes:conventional tillage（CT）,straw return to field（SM）and flat film mulching（FM）;the sub-area was 3 Nitrogen fertilizer treatments:no nitrogen application,20%nitrogen reduction(144 kg·N·hm^-2),conventional nitrogen application(180 kg·N·hm^-2),a total of 9 treatments（CT-N0,CT-N144,CT-N180,FM-N0,FM-N144,FM-N180,SM-N0,SM-N144 and SM-N180）.Taking conventional tillage（CT）as a control,explored the effects of flat film mulch（FM）and straw return（SM）on soil N₂O emissions under different nitrogen levels,and analyzed soil temperature,and assessed relationship of N₂O emissions with soil temperature,water-filled porosity（WFPS）,and nitrate content,ammonium nitrogen content and p H value.The main results of this study were as follows:（1）The N₂O emission flux of nitrogen treatment was between 0.21～75.39μg·（m²·h）^-1,and the annual average N₂O emission flux of no nitrogen treatment was below 2.50μg·（m²·h）^-1.The total N₂O emission of each nitrogen application treatment was between 0.35±0.19～0.50±0.30 kg·hm^-2,and the non-nitrogen treatment was between 0.21±0.11～0.26±0.14 kg·hm^-2.The N₂O emission from the soil of each nitrogen treatment was mainly concentrated within 20 days after fertilization,and the peak of N₂O emission flux occurred within two weeks after fertilization.The N fertilization and film mulching significantly increased N₂O emission flux and total N₂O emission（P<0.05）.Straw incorporated into soil to the field marginal reduced N₂O emissions.（2）Under the condition of nitrogen application,the N₂O emission coefficient and global warming potential of fertilizer nitrogen under the three farming modes of conventional tillage,flat film mulch,and straw return were 0.09～0.10%,60.82～71.71kg·hm^-2;0.15～0.18%,85.62～122.15 kg·hm^-2;0.10%,53.23～69.82 kg·hm^-2respectively.The data of film mulching cultivation was significantly higher than that of conventional tillage and straw returning to the field（P<0.05）.The global warming potential didn’t vary among treatments without nitrogen application.（3）N₂O emissions without nitrogen treatment were only significantly positively correlated with soil water-filled porosity（P<0.05）;however,N₂O emissions were significantly positively correlated with soil water-filled porosity and soil ammonium nitrogen content（P<0.01）under N fertilization.Under conventional tillage,soil N₂O emission flux was significantly positively correlated with soil water-filled porosity and soil ammonium nitrogen content（P<0.01）;nevertheless,soil N₂O emission flux was correlated with soil water-filled porosity,soil nitrate nitrogen content and soil ammonium nitrogen content are significantly positively correlated（P<0.05）.Under film mulch,and soil N₂O emission flux was related to soil water porosity,soil ammonium nitrogen content,soil nitrate nitrogen content and soil the 5cm ground temperature were significantly positively correlated under straw incorporated into soil（P<0.05）.It showed that microbial nitrification in dryland soil is the main source of soil N₂O emission,and under the conditions of mulching and straw returning,denitrification soil N₂O emission source.（4）Nitrogen application significantly increased grain yield（P<0.05）.Compared with conventional cultivation,film-mulching cultivation and returning straw to the field increased yield,and even reached a significant level in suitable years.There was no significant difference between 20%nitrogen reduction and conventional nitrogen application rate in grain yield and some yield components,indicating that 20%nitrogen reduction would not cause yield loss.Film mulching and nitrogen application significantly increased the N₂O emission intensity under the yield scale;straw returning to the field had marginal reduction the N₂O emission intensity under the yield scale.（5）The cumulative emission of N₂ under the three cultivation modes of conventional tillage,flat film mulch,and straw return were 0.70～1.30,0.99～1.82 and0.72～0.92 kg·hm^-2.Film mulching cultivation significantly increased N₂ emissions,while straw returning to the field significantly reduced N₂ emissions.In summary,the N₂O emission of winter wheat fields in the Loess Plateau was mainly from nitrification.Under the conditions of film mulching and straw returning,denitrification was also one of the factors affecting N₂O emission.Reducing nitrogen by 20%couldn’t significantly reduce wheat yield;straw incorporated into the field could not only maintain yield,but also reduce greenhouse gas N₂O emissions;film mulching cultivation had a significant yield increase effect,but it increased soil N₂O emission flux,emission intensity and N₂O emission factor for fertilizer nitrogen.