Study On Dynamic Change Of Greenhouse Gas Emission In Wheat Fields In South China And Effect Of Reducing Nitrogen Fertilizers On Organic Materials

Excessive nitrogen application and waste of agricultural resources in southern China,and increased greenhouse gas emissions will become the limiting factor for sustainable agricultural development.From October 2017 to June 2018,the emission fluxes of N₂O,CO₂ and CH₄ and the equivalent CO₂ emissions from agricultural production were dynamically monitored and the net greenhouse effect of farmland was calculated by the method of biomass.The rules of Greenhouse gas emissionThe greenhouse gas emission rule and the net warming effect under different returning modes of organic materials were discussed.The main factors affecting greenhouse gas emissions were discussed,and a reasonable fertilization mode was proposed to provide reference for emission reduction measures in this area.Based on 3 modes of organic material returned(J:straw full returning;JF:straw full returning and cow dung,cow dung 45 m³·hm^-2;JZ:straw full returning and mushroom dregs,mushroom dregs 60 m³·hm^-2)and 2 nitrogen levels(N1:243kg·hm^-2,which is 10%lower than the local conventional nitrogen application),and N2:216 kg·hm^-2,20%less than local conventional nitrogen application),static chamber method and gas chromatography were used to monitor in situ in the field,and the following conclusions were obtained.（1）The greenhouse gas emissions of wheat field ecosystem in southern China,are basically the same under different fertilization modes.The emission of CO₂ and N₂O was mainly concentrated in the jointing stage after fertilization and irrigation,and the peak appeared at jointing stage;the absorption of CH₄ was concentrated in the green-back stage,and the emission was concentrated in the filling stage after heavy rainfall.The return of organic materials to the field reduced the total emissions of CO² and N₂O,which JN2treatment decreased by 30%and 23%respectively,and JZN2 treatment decreased by 23%and 20%respectively;the return of organic materials reduced the total amount of CH₄ emissions.The JFN2treatment reduced by 62%;the three organic materials were returned to the field,and the total amount of N₂O discharged under the slag treatment was lower than that of straw and cow dung,which was reduced by18%and 44%respectively,the total CO₂ emissions of straw is lower than that of cow dung and biogas residue,which is reduced by 12%and 32%,respectively.（2）The correlation analysis shows that nitrate nitrogen and ammonium nitrogen are the main factors affecting N₂O emissions.The N₂O emission fluxes were significantly positively correlated with nitrate nitrogen and ammonium nitrogen,and positively correlated with soil 5cm temperature and soil 10cm temperature.There was no correlation between CH₄ absorption and impact factors.（3）According to the analysis of global warming potential（GWP_A）,the GWP_A of the wheat season is mainly dominated by N₂O and CO₂ emissions,and the GWP _A under straw returning treatment is lower than that of mushroom residue and cow dung.From the perspective of net greenhouse effect,JN1,JFN2and JZN2 were treated as sinks of greenhouse gases,and CK,JN2,JFN1 and JZN1 were treated as sources of greenhouse gases.Compared with CK,organic materials also increased crop yield and net primary productivity of crops to varying degrees,and the improvement of bacterial residue and cow manure treatment was better than straw.In general,the use of agricultural waste is conducive to increasing crop yields while increasing crop productivity and reducing the net greenhouse effect of farmland.（4）The analysis of greenhouse gas emission intensity（GHGI）shows that the combination of organic materials and chemical fertilizers increases wheat yield,and reduces the GHGI in the wheat season,which effectively reduces greenhouse gas emissions per unit of production.Under the conditions of returning the three kinds of organic materials,the yield of slag returning to the field was the highest,which was higher than that of straw and cow dung,which increased by 1719.37 kg?hm^-2 and 1828.30 kg?hm^-2,respectively.The GHGI of the mushroom residue returning to the field was the lowest,which was reduced by 0.06kg?hm^-2 and 0.29 kg?hm^-2 compared with straw and cow dung.（5）In the wheat-sea ecosystem in southern China,the combination of chemical fertilizers and slag significantly increased the yield of wheat.Compared with the single application of chemical fertilizers,the combined application of slag and chemical fertilizer increased yield by 32%to 72%,Considering GHGI,global warming potential,yield and net warming potential,JZN2 treatment,the application of slag fixed carbon 9892.45 kg?hm^-2,yield 8061.34 kg?hm^-2,the net greenhouse effect is-2052.41 kg?hm^-2,which effectively realizes the resource utilization of agricultural resource waste,and takes into account the environmental effects while achieving higher economic benefits.