Emission Characteristics Of CO₂ And CH₄ On Dryland Under Different Long-term Fertilizations

Farmland is one of main sources of greenhouse gases.It has important and instructive meanings for achieving high yield and reducing greenhouse gases emission to study the effects of long-term different fertilizations on CO₂ and CH₄ emission characteristics and its influence factors.This research was based on a long-term rain-fed trial under the rotation of winter wheat-summer fallow on conventional tillage in?National Monitoring Base of Soil Fertility and Fertilizer Efficiency on Loess Soil?.Gas and soil samples were collected from 7treatments as farmland without fertilization?CK?,N fertilizer?N?,N and K fertilizer?NK?,P and K fertilizer?PK?,N and P fertilizer?NP?,N,P and K fertilizer?NPK?,and NPK plus cattle manure?MNPK?.Farmland CO₂ and CH₄ emission were monitored by the static chamber-GC method in situ,and its relationship with soil physic-chemical properties were also analyzed.The main results and conclusion were given as follows:1)MNPK,NPK and NP could significantly increase soil organic matter,total nitrogen,dissolved organic carbon?DOC?and microbial biomass carbon?MBC?,which is helpful to improve soil fertility.2)The peak of soil CO₂ emission flux appeared at the heading stage?mid of April?and mid of August under different fertilization treatments,meanwhile the peak of soil CH₄ uptake flux also appeared.Compared to CK,MNPK,NPK and NP increased soil CO₂ emission flux significantly,but reduced CH₄ uptake flux significantly.Overall,rainfed farmland is a sink of atmospheric CH₄.3)The results of correlation analysis showed that soil organic matter and total nitrogen are the key factors to influence the CO₂ emission and CH₄ uptake.The results of redundancy analysis?RDA?showed that the importance of soil properties for soil CO₂ emission flux was in order as:soil temperature>soil water content>microbial biomass carbon>dissolved organic carbon>NO₃^--N>NH₄⁺-N,while the importance of soil properties for soil CH₄uptake flux was in order as:soil temperature>soil water content>NO₃^--N>dissolved organic carbon>microbial biomass carbon>NH₄⁺-N.Soil temperature and water content affected the CO₂ emission flux by mainly influencing soil DOC and MBC,and affected the CH₄ uptake flux by mainly influencing soil DOC and NO₃^--N.To sum up,long-term MNPK,NPK and NP had significant effects on increase of CO₂emission and reduction of CH₄ uptake,while N,NK and PK had little effects on them.Soil physiochemical properties such as Soil temperature,water content,organic matter,total nitrogen,pH,MBC,DOC,NO₃^--N and NH₄⁺-N could affect soil CO₂ emission and CH₄uptake.It couldn't fully evaluate the effects of different fertilizations on atmospheric greenhouse gas CO₂,and it needs to be comprehensively judge that the soil-crop ecosystem is a sink or source of atmospheric greenhouse gas CO₂ on rainfed farmland by integrating crop photosynthesis and assimilating production?crop biomass?as well.