Effects Of Different Amendments On The Dynamics Of Greenhouse Gas Emissions In Dryland Orchards

The Loess Plateau has serious soil erosion and prominent ecological environmental problems.Apple planting,as the main guiding industry for returning farmland to forests（grass）,has promoted local economic development.However,due to the low and uneven distribution of inter-annual precipitation in the area,unreasonable orchard management measures,and a large amount of fertilization,the soil water environment in the local apple orchard has gradually deteriorated and the soil carbon pool has decreased,which has accelerated the rate of soil carbon emissions.Increased greenhouse gas emissions,which in turn led to a series of environmental problems.In order to achieve the national strategic goal of"carbon peak and carbon neutrality",respond to global climate change,effectively increase ecological carbon sinks in the Loess Plateau,and strive to achieve"net zero carbon emissions"from dryland apple orchards.This article mainly discusses the effects of different soil amendments on the greenhouse gas emissions of the dryland apple（Malus pumila Mill）orchard in the loess hilly area.A blank control（CK）,Bacillus glaci（JZ）,Bacillus subtilis（KC）,and biochar（BC）and macromolecular water retention agent（SAP）5 treatments,using static box method to monitor greenhouse gas（CH₄,CO₂ and N₂O）emissions,and comprehensively analyze and evaluate the carbon sequestration and emission reduction effects of different soil amendments in dryland orchards.Research indicates:（1）The change characteristics of soil physical and chemical properties after applying soil amendments to dryland apple orchards in the loess hilly region were explored.During the test period,the average WFPS of 0-100 cm treated with CK,JZ,KC,BC and SAP was 43.76%,47.73%,41.32%,42.44%and 45.30%,respectively.Compared with CK,the average soil moisture content of 0～100 cm treated with JZ,KC,BC and SAP increased by 9.07%,-5.58%,-3.02% and 3.52%,respectively,and the surface moisture content increased by 11.73%,0.50%,13.83%,and 8.67%,respectively.The soil water content at different depths of CK,JZ and KC treatments all showed the middle layer>deep layer>surface layer,and the BC and SAP treatments showed the surface layer>medium layer>deep layer.The average soil temperature of each treatment was 17.64,17.94,17.85,17.10 and 18.98℃,respectively.The soil temperature of 0-5cm was affected by air temperature and fluctuated greatly.Compared with the control,the JZ,KC and SAP treatments increased by 0.96,0.81 and 2.49℃,and the BC treatment decreased by 0.99℃.The SOC change of the average soil organic carbon content of0-100cm is BC>SAP>JZ>KC>CK.The SOC content of the soils treated with BC,JZ and KC was significantly higher than that of the control（P<0.05）,and the SOC treated with BC was at 0-20cm,The SOC content of the three soil layers at depths of 20-40cm and 40-60cm has a significant improvement effect.After applying soil amendments in 2019,the pH value of the soil at 20-60cm of BC treatment was significantly higher than other treatments,and the soil pH at depths of 20-40cm and 40-60cm were 8.79 and 8.54,respectively.In 2020,0-20cm soil layer the pH value of the depth JZ,KC,BC and SAP treatment was higher than that of the CK treatment;the pH value of the soil at different treatment depths from 20 to 100 cm showed the order of JZ>KC>BC>CK>SAP.（2）Clarified the dynamic effects of different amendments on the greenhouse gas emissions of dryland apple orchards.In 2019,the average absorption fluxes of CH₄ treated by CK,JZ,KC and BC were 0.062,0.056,0.066,and 0.051 mg·m^-2·h^-1,respectively,and the average emission fluxes of CO₂ were 370.16,355.03,324.47,and 227.43 mg·m^-2·h^-1,respectively.The average emission fluxes of N₂O are 17.96,20.03,19.13 and 23.55μg·m^-2·h^-1,respectively.The average absorption fluxes of CH₄ treated by CK,JZ,KC,BC and SAP in2020 are respectively are 0.198,0.181,0.160,0.155 and 0.167 mg·m^-2·h^-1,and the average CO₂ emission fluxes are 378.74,296.73,250.51,215.61 and 376.14 mg·m^-2·h^-1,respectively.The average N₂O emission fluxes are 378.74,296.73,250.51,215.61,and 376.14 mg·m^-2·h^-1,respectively.The amounts were 51.60,51.29,35.45,35.64 and 57.10μg·m^-2·h^-1,respectively.After applying Bacillus glaci,biochar and macromolecular water-retaining agent to the soil,it will reduce the absorption effect of dryland apple orchard soil on CH₄ in the air;the treatment of biochar and Bacillus glaci significantly reduces CO₂ emissions（P<0.05）,Biochar,Bacillus coli and Bacillus subtilis treatments reduced N₂O emissions compared with the control treatment,and Bacillus subtilis and biochar treatments significantly reduced N₂O emissions.（3）Clarified the correlation between environmental factors and greenhouse gas emissions,and evaluated each treatment in combination with the two indicators of global warming potential GWP and greenhouse gas emission intensity GHGI.Soil temperature is significantly correlated with three greenhouse gas emission fluxes.Among them,CH₄ fluxes treated by CK,JZ,KC,BC,and SAP show a significant negative correlation with temperature,and CO₂emission fluxes are significantly positively correlated with temperature.The N₂O emission flux is significantly positively correlated with temperature.KC and SAP treatment CH₄ flux is significantly positively correlated with WFPS;CK treatment CO₂ emission flux is significantly positively correlated with WFPS,while JZ,KC and BC treatment CO₂ emission flux is significantly negatively correlated with WFPS;CK treatment N₂O emission flux was a significant negative correlation with WFPS during the 2019 test period,and a significant positive correlation with WFPS during the 2020 test period.The N₂O emission flux treated by JZ was significantly positively correlated with WFPS,while the N₂O emission flux treated by KC,BC and SAP was significantly positively correlated with WFPS.Significantly negative correlation.Soil SOC is extremely significantly positively correlated with the total amount of CH₄ absorption,extremely significantly negatively correlated with the total amount of CO₂emissions,and extremely significantly negatively correlated with the total amount of N₂O emissions.Soil pH is extremely significantly positively correlated with the total amount of CH₄ absorption,significantly negatively correlated with the total amount of CO₂ emissions,and extremely significantly negatively correlated with the total amount of N₂O emissions.A comprehensive analysis of the evaluation indicators of GWP and GHGI for different treatments found that biochar can significantly reduce GWP and GHGI by reducing the contribution of CO₂ emissions to GWP,and play a role in water conservation,production,efficiency,and emission reduction in dry land apple orchards in the Loess Plateau.In summary,among the four amendments,Bacillus glaci significantly increased soil pore water content,soil temperature,soil organic carbon,soil p H and apple yield,and significantly reduced CO₂ emissions and GHGI;Bacillus subtilis significantly increased Soil organic carbon,soil p H and apple yield,and significantly reduce CO₂ emissions,GWP and GHGI;macromolecular water retaining agents significantly increase soil pore water content,soil temperature,soil organic carbon and apple yield,and significantly reduce CO₂ emissions and GHGI;and biochar has the most outstanding comprehensive effect in increasing soil moisture content,soil organic carbon and pH,and reducing greenhouse gas emissions.Therefore,it is recommended to apply biochar to dryland apple orchards to achieve the effect of water retention,carbon fixation and emission reduction.