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

Farmland is both a source of greenhouse gas and a potential carbon sink.It is important to study the effects of long-term different fertilizations on CO₂ and CH₄ emission characteristics and its influence factors,and even for the achievement and management of the potential emission reduction of farmland soil as a carbon sink.This research was based on a 26 years' long-term rain-fed trial in “National Monitoring Base of Soil Fertility and Fertilizer Efficiency on Loess Soil”.Gas and soil samples were collected from treatments as farmland without fertilization?CK?,farmland with 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 under the rotation of wheat-fallow system,and also its relationship with soil physic-chemical properties were analyzed to explore the effects of long-term fertilization on greenhouse gas emission in rain-fed dryland in order to select reasonable fertilization on the reduction of greenhouse gas emission and to provide the decision-making basis for sustainable utilization of anthropgenic loess soil.The main results and conclusion are given as follows:1)The peak of soil CO₂ emission appeared at heading stage?mid and late April?and mid to late August under different fertilization treatments.The peak of soil CH₄ absorption also appears at heading stage.Compared to CK,Organic and inorganic combination?MNPK?and balanced fertilization?NP and NPK?increased soil CO₂ emission significantly,but reduced CH₄ absorption significantly.2)The ratio of crop carbon fixation to soil carbon emission was affected by long-term fertilization,and further to influence the carbon balance characteristics of soil.From the NEP values of wheat growing season,farmland soils were “sinks” of atmospheric CO₂ in Organic and inorganic combination and balanced fertilization treatment.But after fallow,net ecosystem productivity?NEP?of all farmland soils are positive,soils are “source” of atmospheric CO₂ emissions,Fallow is not conducive to soil carbon fixation.3)Long-term organic and inorganic fertilizers?MNPK?and balanced fertilization?NP and NPK?could significantly increase soil organic matter,total nitrogen,dissolved organic carbon?DOC?and microbial biomass carbon?MBC?,reduce soil pH,which is helpful to improve soil fertility.4)Soil organic matter and total nitrogen were important for the accumulative emissions of farmland CO₂ and CH₄,and displayed a highly significantly positive correlation with them.The result of redundancy analysis?RDA?showed that the importance of soil properties for soil CO₂ and CH₄ source and sink in order was as 5cm soil temperature > 10 cm soil temperature > soil water content > microbial biomass carbon > dissolved organic carbon > NO3--N > NH4+-N > microbial biomass nitrogen,which temperature,moisture,microbial biomass carbon and dissolved organic carbon are important for CO₂ and CH₄ source and sink.To sum up,the long-term MNPK,NPK and NP had a significant effect on emission characteristic of CO₂ and CH₄,and physiochemical properties of anthropogenic loess soil,while N,NK and PK treatments had a smaller effect on them.Soil temperature,water,organic matter,total nitrogen,pH,MBC,DOC,NO3--N and NH4+-N could be used to predict the emission amount of soil CO₂ and CH₄,which was of great theoretical and practical significance in guiding soil fertilization and monitoring environmental changes.The combination of inorganic fertilizer and organic manure,and balanced fertilization could improve soil fertility and the function of dryland soil as carbon sink,which was of great significance to promote the stability and health of soil ecosystem,and to retard the greenhouse gas effects.