Effects Of Straw Returning Method And Nitrogen Application Level On Soil N₂O Emission In Wheat-maize Rotation System

As one of the three major greenhouse gases,N₂O has an important impact on climate change,and agricultural production is the main emission source of N₂O in the atmosphere.Therefore,it is of great significance to study the emission of N₂O from farmland soil to deal with global climate change.This study of winter wheat and summer maize rotation soil in guanzhong area as the research target,split plot design was used,the main area for nitrogen levels,respectively,the conventional N（G）and 70%nitrogen 70%（G）,deputy district as the straw returned way,straw returning no（N）,respectively,straw returned（S）and returning straw+biochar（SB）.The effects of each treatment on soil N₂O emission and soil physicochemical properties were analyzed,and the correlation between soil N₂O emission and soil physicochemical properties was discussed.The following results were obtained:（1）No matter the wheat season or the maize season,the N₂O emission flux of the farmland soil during the crop growth period showed the same trend.Specifically,within 5-16days after sowing and fertilization,the N₂O emission flux increased sharply and reached the peak one after another;then,with the advance of time,the N₂O emission flux decreased rapidly and remained in a low level range for a long period of time.In addition,the sub-peak of N₂O emission also appeared correspondingly after rainfall.Soil N₂O emission flux had an obvious seasonal variation,which was the lowest in winter and kept at a low level from overwintering period to jointing period of winter wheat.（2）The total N₂O emission of each treatment in the whole growth period of maize season was higher than that of wheat season.At the same nitrogen application level,straw returning can increase the total N₂O emission from soil,while straw returning and biochar can reduce the total N₂O emission,and nitrogen reduction can also inhibit the N₂O emission.（3）Straw returning has a certain effect on soil heat preservation and soil moisture conservation,and straw returning+biochar also has a role in soil moisture conservation.Compared with straw returning and straw returning+biochar,the contents of SOC and DOC in the soil were significantly increased,but the content of MBC in the wheat season was decreased.The contents of TN,DON and inorganic nitrogen in the soil were significantly increased under the straw returning treatment.Straw returning+biochar could also increase the contents of TN and NO₃^--N in the soil,but the content of NH₄⁺-N was lower than that under the straw returning treatment,even lower than that without straw in the wheat season.Nitrogen reduction can effectively reduce soil TN and inorganic N contents,increase DOC content in wheat season,reduce microbial biomass C and N content,and decrease SOC content in corn season,increase microbial biomass C and N content.（4）Each treatment had no significant effect on the enzyme activity in maize season.In the wheat season,the activities of various enzymes under conventional N application were lower than those under reduced N application.Under conventional N application,the urease activity of straw returning was significantly lower than that of other treatments.Both straw returning and straw returning+biochar could increase nitrate reductase activity,but had no significant effect on nitrite reductase activity.（5）There is a significant positive correlation between N₂O emission flux and soil water and heat conditions.In wheat season,soil N₂O emission flux is positively correlated with soil MBC,SOC,DON,MBN and soil SOC:TN,and negatively correlated with soil TN,DOC,DOC:DON and MBC:MBN.In maize season,soil N₂O emission flux is positively correlated with the contents of DON,SOC,TN,DOC,SOC:TN,MBC:MBN,and negatively correlated with the contents of MBC,MBN and soil DOC:DON.By means of linear fitting,there is a significant or extremely significant positive correlation between NO₃^--N and NH₄⁺-N content and N₂O emission flux in the wheat growing season,while there is an extremely significant positive correlation between N₂O emission flux and NH₄⁺-N content and nitrification and denitrifying enzyme activity in the corn growing season.Comprehensive analysis shows that nitrogen fertilizer reduction combined with straw+biochar input is an effective measure to achieve rational and efficient utilization of resources and greenhouse gas emission reduction in Guanzhong region.