Decomposition Of Green Manure And Its Impacts On Soil Greenhouse Gas Emission And C And N Fractions In Dry Land Farming Systems

As an organic fertilizer source,green manure is expected to play an important role in the national strategy of reducing application and increasing efficiency and“storing grain in the ground and storing grain with technology”.The residual decomposition and nutrient release process of green manure after plowing into the soil are the key links to determining the effectiveness of green manure,which needs to be discussed in depth for specific crop systems.In this thesis,the in-situ bag-embedding method was used to study the decomposition of four green manures（crimson clover,vetch,ryegrass,and oat）in two systems of bare land system and maize planting system,systematically observed its impacts on soil greenhouse gas emission and C and N fractions to provide a theoretical basis for the rational use of green manure in dry land planting systems.The study found that:（1）The trend of cumulative decomposition rate of green manure in different treatments was similar,showing a trend of rapid increase,medium and low speed increase,and slow increase gradually stabilized.Decomposition and nutrient release were mainly concentrated in 6 weeks of the experiment,The cumulative decomposition rate reached more than 50%,the carbon release rate reached 55-74.5%,and nitrogen release rate reached 57-76%.On the 130^thday after the decomposition of green manure,the cumulative decomposition rate of each treatment reached more than60%.The cumulative decomposition rate of green manure in the maize planting system was higher than that in the bare land system,which was 1.07,1.04,1.01 and1.04 times respectively.（2）The global warming potential（GWP）of each green manure treatment was positive,indicating that the tested farmland system was the source of greenhouse gas emissions.Compared with the bare land,the maize planting system increased the daily mean CO₂and N₂O flux by 16.27 and 9.72%,respectively,while reducing the daily mean CH₄flux by 54.05%.Compared with the control treatment（without adding green manure）the addition of oat,ryegrass,vetch,and clover residues increased the daily mean CO₂flux by 17.91,22.36,28.01 and 31.25%,and the daily mean N₂O flux increased by 18.10,32.76,41.38,and 56.9%,respectively.While reducing the daily mean CH₄flux by 84.17,69.39,51.02,and 30.61%,respectively.（3）Soil organic carbon showed an upward trend after the decomposing of the green manure.The soil organic carbon content in the bare soil decreased and stabilized after two weeks of green manure decomposition.In the maize planting system,the soil organic carbon content was higher in the filling and the harvest period.Compared to the initial days,the soil microbial biomass carbon（MBC）and soil potential mineral carbon（PCM）content was higher at the end of the experiment,and the organic carbon was returned to the initial level.Compared with the maize planting system,the bare land system significantly increased MBC and PCM by 8.2 and 9.78%.Compared to control,the addition of green manure residues significantly increased soil microbial biomass carbon（MBC）by 2.79-11.89%and soil potential mineral carbon（PCM）by6.21-19.61%.（4）The dynamics of soil total nitrogen and ammonium nitrogen in bare land systems are basically similar to the changes in organic carbon.In the maize planting system,the nitrate nitrogen content of each treatment showed a changing trend of first rising,then falling,and then slowly rising.Similarly,soil total nitrogen and ammonium nitrogen content of each treatment increased at seedling,filling,and harvest of the decomposition.Compared to control treatment（without adding green manure）,the addition of green manure residues significantly increased soil microbial biomass nitrogen（MBN）by 2.02-22.85%and soil potential mineral nitrogen（PNM）by2.65-11.15 mg/kg.In summary,green manure,as an organic material,will release nutrients and improve soil fertility during decomposition,but the increased input of carbon and nitrogen will also stimulate soil greenhouse gas emissions.Therefore,in practice,it is necessary to seek a balance between farmland fertility improvement and greenhouse gas emissions in specific regions.