Study On Scale Effect And Its Influencing Factors In The Scenario Of Simulating Soil Organic Carbon Dynamics In The Upland

Agro-ecosystem models have been extensively used to predict changes in soil organic carbon(SOC)in farmland in the scenario of climate and farmland management measures change in the future.However,currently most of the studies rely on maps of only one or certain one scale,and little has been done on influence of map scales on prediction of SOC dynamics in the scenario of different climate and farmland management measures.Based on the uplands in North Jiangsu,China,the 1980-2009 meteorological data and 2009 farmland management data of the region,soil databases of six different mapping scales,i.e.,1:50 000,1:250 000,1:500 000,1:1 000 000,1:4 000 000,and 1:10 000 000,and different climate and farmland management measures scenarios set for the period of 2010-2039,this study used the DNDC model to predict carbon sequestration rate and potential as affected by different climate and farmland management measures in the region with the data of the most detailed 1:50 000 map and quantify the uncertainties of using the soil databases different in mapping scale to simulate SOC dynamics in the upland-crop ecosystem.The main research conclusions were as follows:1.The scenario analysis of upland in the northern Jiangsu Province from 2010 to 2039 on the 1:50 000 map showed that,the whole region turned out "carbon sink" effect.When at different climate change scenarios the carbon sequestration rate showed little change,the average annual C sequestration rate were between 291 to 373 kg C hm-2 y-1.the total SOC changes were between 34.25 to 43.98 Tg C.the carbon sequestration rate showed large changes in different traditional agricultural management scenarios,the average annual C sequestration rate were between 59 to 1317 kg C hm-2 y-1.The total SOC changes were between 6.93 to 155.11 Tg C.The simulation results of different soil groups indicated that,fluvo-aquic soil,saline soil,cinnamon soil,brown soil,purplish soil and lime concretion black soil would all exert strong"carbon sink" effect in different climate and agricultural management practices,with average aUnual C sequestration rate between 47 kg C hm-2 y1 to 1356 kg C hm-2 y1,and the total SOC change varied from 0.02 Tg C to 84.09 Tg C.Relatively speaking,lithosols soil and limestone soil would exert weak "carbon source" effect at the no nitrogen fertilizer scenario,the average annual C sequestration rate were-38 kg C hm-2 y-1 and-3 kg C hm-2y-1,the average annual C sequestration rate of lithosols soil and limestone soil were varied from 83 to 983 kg C hm-2 y-1,and the total SOC change varied greatly from 0.02 to 1.71 Tg C.In view of that we can come to the conclusion that,the climate and agricultural management practices were conducive to accumulate soil organic carbon in addition to the lithosols soil and limestone soil at the no nitrogen fertilizer scenario,it also showed that taking the reasonable measures may have great effectively role in accumulating soil organic carbon in the region.2.The scenario analysis of upland in the northern Jiangsu Province from 2010 to 2039 on the 1:250 000,1:50 000,1:100 000,1:400 000 and 1:1 000 000 map showed that,the prediction varied sharply with the scale of the map that was used.When the average annual C sequestration rate predicted based on the 1:50 000 map was used as baseline,the use of the other maps would generated deviations ranging from 2.28%to 22.73%.The generated deviations of simulation results at each scale is 1:50000>1:250 000>1:1 000 000>1:100 000>1:400 000.The generated deviations of different soil groups indicated that,saline soil,cinnamon soil,brown soil showed more generated deviations on the 1:1 000 000,1:400 000 and 1:1 000 000 maps.The impact of different soil resolution databases on farmland management measures was less than that of climate change,The average annual SOC changes and the total SOC change generated deviations of former were ranging from 0.15%to 62.48%and0.02%to 60.83%respectively;The average annual SOC changes and the total SOC change generated deviations of latter were ranging from 0.07%to 41.64%and 0.01%to 40.36%respectively.Different soil groups showed that,subject to different resolution database,limestone soil and lithosol had greater impact,The generated deviations of the average annual SOC changes from 3.95%to 1669.23%and 2.76%to 1669.23%respectively.And subject to different resolution database,fluvo-aquic soil,saline soil,cinnamon soil,'brown soil,purplish soil and lime concretion black soil had less affected,The generated deviations of the average annual SOC changes from 0%to 62.14%,0.56%to 72.34%,1.60%to 67.31%,1.41%to 61.03%,0.41%to 95.83%and 1.71%to 88.70%respectively.It is,therefore,essential for studies in the future to use soil maps of large scales for data in quantifying regional SOC dynamics.3.The analysis of the affected factors for the changes of soil organic carbon in the northern Jiangsu Province,different resolution soil database showed significant negative correlation with the average annual SOC changes at the levels of p<0.001,The factors that lead to the significant effect of scale effect are soil initial organic carbon,clay content,bulk density and pH.The initial soil organic carbon and clay content showed significant negative correlation with the average annual SOC changes at the levels of p<0.001 in almost Scenarios,which could interpret the variation of the average annual SOC changes form 2.5%to 66.20%and 3.8%to 38.40%at the different Scenarios.Relatively speaking,bulk density and pH had less affected and were unstable.Therefore,in the study of organic carbon simulation,in order to reduce the uncertainty of the simulation results,it is necessary to establish a more accurate soil database on a large area scale in the future.