Study On The Response Of Main Crops Yield And Soil Carbon Sequestration And Greenhouse Gas Emission Under Different Fertilization Practices To Future Climate Change In Bohai Rim

Carbon?C?and nitrogen?N?cycling processes in agroecosystems are modified with changes in hydrothermal conditions and atmospheric CO₂ concentrations under climate change.Quantifying the impact of different fertilization strategies on crop yields,soil organic carbon?SOC?and N₂O emissions under future climate change is the basis to ensure sustainable agricultural development.Therefore,this thesis focused on Bohai rim,evaluated the effects of different fertilization strategies on crop yields,SOC and N₂O emissions at site and regional scales under different future climate scenarios,which based on a combination of sites experiments and regional simulations,process modeling?DNDC?and machine learning?Random Forest algorithm?.This thesis would provide a new approach to study the response of agroecosystems to climate change and provide a scientific basis for future fertilization strategies selecting.The main results are as follows:?1?Multi-year studies in spring maize fields demonstrated that,compared with farmer‘conventional N fertilization?FP?,N reduction and organic manure replaced 50%fertilizer N amount?RMN?could reduce N₂O emissions.Organic manure or maize straw input could enhance SOC storage?P<0.001?,and carbon sequestration efficiency of maure was higher than that of maize straw?0.26 vs 0.12?.The average net GHG emission was 203 kg CO₂ eq ha^-1yr^-1under FP,was net GHG sources.The other treatments could convert net GHG sources under FP to GHG sinks.By considering yields and net GHG emissions,RMN could be an optimal management option.?2?Winter wheat-summer maize field experiment showed that the fertilizer N application significantly promoted to N₂O emission?P<0.05?,and the straw return significantly?P<0.05?increased the SOC storage in the field.30%N reduction and 30%N reduction intergated with straw return treatment could maintain yields and convert the net GHG sources under farmer‘conventional N fertilization to sinks,reduce net GHG emissions(1997-3094 kg CO₂ eq ha^-1 yr^-1).?3?DNDC model was validated using the monitored crop yields?Huantai,Qianxi and Hengshui?,SOC changes?Changping,Qianxi and Hengshui?and N₂O emissions?Huantai,Qianxi,Qingxian,Huantai,Luan County,Linghai and Dalian?.The accuracy?R²?of winter wheat yield,maize yield?spring and summer maize?,SOC and total N₂O emissions validations were 0.76,0.82,0.66 and 0.72,respectively,indicated that the DNDC model could simulate the C and N cycling processes of major crops well in Bohai rim.?4?For spring maize fields,the average net GHG emission increased from additonal organic maure was-16.5 kg CO₂ eq ha^-1 yr^-11 under the RCP4.5 and RCP8.5 scenarios,and for winter wheat-summer maize fields,the increase rate of net GHG sinkwas highest uner straw return(-14.13 kg CO₂ eq ha^-1 yr^-1).By considering yields and net GHG,the additional organic matter?organic maure and straw?or RMN could balance yield,dSOC and N₂O emissions.?5?DNDC-RF model was established based regression between input variables and the DNDC outputs through RF algorithm.The responses of crop yields,SOC and N₂O under different manage practices?conventional fertilizer?FP?,additional manure?MFP?,straw return?SFP?,and replace 50%N with manur?RMN??to the climate change?2008-2100?in the Bohai rim were predicted by DNDC-RF model.The results showed that,spring maize yields under the RCP4.5 were a decreasing trend,with an annual yield reduction of 0.89 kg C ha^-1.For summer maize yields,there showed an increase in future climate change,with the fastest increase in MFP under the RCP8.5(26 kg C ha^-1 yr^-1)and higher increase rate in southeastern Shanxi province.For winter wheat yields,there showed increases under future climate change,with the highest increase in SFP measures under the RCP8.5(17.1 kg C ha^-1 yr^-1),with a higher increase rate in central Hebei province.?6?For spring maize fields dSOC,there showed the highest increase in SFP under the RCP4.5(36.95kg C ha^-1 yr^-1),with higher increase rates in western Liaoning province and northern Hebei province.For winter wheat-summer maize fields dSOC,there was highest increase in MFP under the RCP8.5(109 kg C ha^-1 yr^-1),with higher increase rates in southeastern Hebei province and Jiaodong Peninsula.For spring maize fields N₂O emissions,there was the highest increase rate under the RCP8.5(4.2×10^-3kg N ha^-1 yr^-1),with a higher increase rate in eastern Hebei Province?i.e.,Qianxi?.For winter wheat-summer maize fields N₂O emissions,there was highest in MFP under the RCP8.5(1.7×10^-2 kg N ha^-1 yr^-1),with a higher increase rate in eastern and central Shandong province.For spring maize fields net GHG emissions,there were net GHG sinks under fertilization practices,and net GHG sinks was highest for SFP under different RCP scenarios.When the scenario changes from RCP4.5 to RCP8.5,for winter wheat-summer maize fields,the overall net GHG performance under FP was changed from sinks to sources(25 kg CO₂ eq ha^-1 yr^-1).However,SFP,MFP and RMN could convert the net GHG sources under FP to net GHG sinks,and MFP was the best practice to achieve this convert(25 kg CO₂eq ha^-1 yr^-1).