A Observation Study In Situ On Greenhouse Gases Emissions In Conventional Piling And Windows Composting Processes Of Agricultural Residual

Our goals were to explore the mechanism of GHGs emissions in the conventional piling(CF)and windows composting(OF)processes of agricultural residual.Also,we hoped we could provide some reliable data and theories for estimating global GHGs emissions and exploring the way of reduction.In this paper,we chose the livestock,poultry manure and crop straw as the main raw materials.We conducted an observation experiment in situ to study the scenarios of GHGs emission fluxes in CF and OF.Physicochemical factors were considerd to preliminarily elucidate their effects on GHGs emissions,and then we compared the differences of GHGs emission between CF and OF processes.The main results were as follows:The CF or OF process of agricultural residual released the majority of CO2 during the first 21 days,and released the majority of CH4 during 28～42 days and 0～21 days,respectively.N2O emissions were mainly derived from 12～28 days for CF process,and 43～62 days for OF process.The maximum peak of CO2 emission fluxes occurred at the beginning and reached 58.78 mg·kg-1 hr-1 for CF,and the macimun preak of CH4 occurred on 10th day and reached 0.41 mg·kg－1·hr-1.However,N2O emission fluxes had a special peak as high as 78.73 μ·kg-1·hr-1 on 21th day in the CF process due to severe interference when the pile was moved.In the OF process,the maximum peak of CO2 and CH4 emission fluxes both occurred on the fourth day and reached 135.27 and 1.19 mg·kg-1·hr-1 respectively,and the N2O emission flux increased to the maximum peak at 9.01 μg·kg-1·hr-1 by the end.Compared with the CF,the OF process increased CO2 and CH4 emissions by 226.2%and 374.6%,respectively,but reduced 72.5%N2O emission.In the CF and OF process,CO2 as main carbon loss form accounted for 8.79%and 17.74%of the initial TOC respectively,and a carbon loss form of CH4-C only accounted for 0.13%～0.33%for the two processes.Nitrogen loss in the form of N2O emission accounted for 0.11%and 0.04%of TN for CF and OF process,respectively.In addition,the amount of GWP100 was produced by three GHGs emissions which CO2 accounted for about 80%of the total amount,and secondary GHGs emission was CH4.Agricultural residual OF treatment significantly increased about 217%GWP100 production relative to CF treatment.In the CF or OF process,MC and TOC were the main factors on CO2 emission.About 79.93%of CO2 emissions could be explained by the MC when ignored time and space differences.The TOC and CO2 emission had significant linear positive correlation and the trend line slope close to the same value under the conditions of CF or OF treatment,no matter at low or high level.Besides,pH,TN and C/N would partly influence CO2 emission in the CF process.PT and TOC were main factors that affected CH4 production in the CF process.However,MC and TOC were main factors that influenced the CH4 emission in the OF process.In the CF or OF process,PT,NH4+-N and NO3--N were all the important factors that impacted N2O emission.Furthermore,MC was also a major factor affecting N2O emission in OF,and N2O had a certain degree of response to variations of pH and TN in CF.