Effects Of Long-term Fertilization On Greenhouse Gas N₂O Emission In Rain-fed Farmland

Global warming caused by the increase of greenhouse gas emissions has been becoming a global environmental focus.Scientists from all over the world paid attention to N₂ O more and more because of its strong greenhouse effect and destructive effects on troposphere O3.The agricultural production process,as a main source of greenhouse gas N₂ O,is an important object during the research of greenhouse gas emission and global climate change.In this study,dynamics of greenhouse gas N₂ O emission from rain-fed farmland were studied by static chamber-GC method in situ under long-term different fertilizations at the farming system of winter wheat/summer fallow in “National Loess Fertility and Fertilizer Benefit Monitoring Base”.Meanwhile physical and chemical properties of soil were monitored under different fertilizations,and their relationships with greenhouse gas N₂ O emissions were analyzed also.The results indicated as follow.1)Under different fertilization treatments,the dynamic trend of greenhouse gas emission fluxes was consistent throughout the monitoring period.In the soil-crop system,average N₂ O emission flux?12.98 ug·m-2·h-1?and cumulative emission?1.14 kg·hm-2?were the highest under the organic-inorganic fertilizer?MNPK?.Average N₂ O emission flux?5.92 ug·m-2·h-1?and cumulative emission?0.52 kg·hm-2?were the lowest under PK treatment.In the case of bare soil,the treatment with no fertilization?CK?was the lowest that the average flux was only 7.08 ug·m-2·h-1,and the annual accumulated flux was 0.62 kg ·hm-2.2)The cumulative emission of N₂ O during the wheat season was higher than that during the fallow season.There was no significant difference in the cumulative emissions between bare soil and soil-crop system.The cumulative emission of greenhouse gas N₂ O in soil-crop system were increased by 0.36 and 0.47 kg·hm-2 to compare N with CK,and to compare PK with NPK,respectively.Compared with NPK treatment,the cumulative emission of greenhouse gas N₂ O were all increased during wheat season and during fallow stage in MNPK.Both N fertilizer application and organic manure application promoted the emission of greenhouse gas N₂ O significantly.3)The grain yields of winter wheat were quite different under different long-term fertilization treatments.The grain yield of MNPK was the highest,which was not significantly different from that of NPK,but it was significantly higher than that of other treatments.The yield of N was the lowest.4)Long-term NP,NPK and MNPK could significantly reduce soil pH,and increase soil organic matter and total nitrogen.During the whole monitoring period,the change trend of ammonium nitrogen in topsoil was the same,and the difference was not obvious.The peak of ammonium nitrogen appeared just after fertilization and over wintering.Nitrogen application significantly increased nitrate nitrogen in topsoil,and it was the most significant in MNPK treatment.The average content of nitrate nitrogen in topsoil of MNPK was 16.02 mg·kg-1,which was 4.52 mg·kg-1 higher than that of NPK,and was 9.02 mg·kg-1 higher than that of CK.The dynamic tendency of soil microbial biomass carbon and nitrogen were same for all treatment,but the effect of different fertilizations on microbial biomass nitrogen differed less,in which MNPK increased the soil microbial biomass C and N content significantly.5)The emission flux of greenhouse gas N₂ O was highly significantly positively correlated with air temperature,soil temperature at 5cm and 10 cm depth,soil moisture,soil ammonium nitrogen,soil nitrate nitrogen,soil microbial biomass nitrogen and microbial biomass carbon?p<0.01?,significantly positively correlated with soil organic matter and total nitrogen,and significantly negatively correlated with soil pH.The results of multiple regression analysis showed thatY1?N₂O emission flux?=-13.753 + 61.695X1?soil moisture?+ 0.483X3?10cm soil temperature?+ 0.018X6?microbial biomass nitrogen?,in which 3 variables could explain 38.7% of soil N₂ O emission amount?P <0.01?.Y2?N₂O cumulative emission?=1.248 + 0.121X2?5cm soil temperature?+ 1.369X6?microbial biomass nitrogen?,in which the 2 variables could explain 91.2% of the cumulative emission of N₂O?P <0.01?,and could predict the cumulative emissions of N₂ O well.