Simulation Of Temporal And Spatial Evolution Of Soil Organic Carbon In Dryland At Regional Scale

Changes in soil organic carbon(SOC)in agricultural soils influence soil quality and greenhouse gases(GHGs)concentrations in the atmosphere.Carbon sequestration in agricultural soils can not only mitigate climate change,but ensure world food security as well.Recommended management practices(RMPs),such as reduced tillage,no tillage,and crop residue return,have great potential to increase the amount of SOC sequestered in agricultural soils.Uplands cover more than 70%of the overall cropland area in China and would play an important role in sequestering the atmospheric carbon dioxide(CO2).Therefore,carrying out research on SOC dynamics and carbon sequestration potential for uplands of regional scale is of great significance in realizing the sustainable development of agriculture,and providing scientific evidence and theory support for making the emission inventory of greenhouse gases and the strategy of carbon sequestration in cropland soils of regional scale.The SOC models are useful tools for analyzing the mechanisms controlling SOC dynamics in agricultural soils and inferring changes in SOC at larger spatial scales.They provide us with a necessary means of predicting,monitoring,and verifying carbon sequestration potential of cropland soils under diverse RMPs scenarios.The Century model is one of the most extensively used and well validated SOC models worldwide.In this study,based on data from nine long-term upland soil fertility monitoring sites,SOC dynamics for uplands at field scale was first simulated and validated by the Century model.Then taking Anhui province as an example,SOC dynamics for uplands at regional scale was modeled based on the 4 109 upland-soil polygons extracted by using spatial overlay analysis of the 1:500 000 soil database and thel:500 000 landuse database.The principal conclusions were summarised as follows:The field-scale model validation results indicated that the Century model could satisfactorily simulate SOC dynamics for uplands of China across typical soil types,cropping systems and management regimes.Considering the regional validation results,the Century model performed relatively well in modelling SOC dynamics for uplands in Anhui province.The area-weighted mean soil organic carbon density(SOCD)for uplands of the province increased from 18.77 Mg C ha-1 in 1980 to 23.99 Mg C ha-1 in 2008 with an average sequestration rate of 0.18 Mg C ha-1yr-1.Over the past 29 years,the net SOC gain in upland soils of the province was 19.37 Tg,with an average sequestration rate of 0.67 Tg yr-1.Augmentation of SOC was primarily due to increased consumption of nitrogen fertilizer and farmyard manure.From 1980 to 2008,approximately 94.9%of the total upland area sequestered carbon while 5.1%lost carbon.Moreover,SOC dynamics were highly differentiated among upland soil groups.Scenario analysis results clearly indicated that RMPs had great potential to sequester carbon in upland soils of China.Increasing crop residue return was the most effective management practice for carbon sequestration.During the next 20 years,carbon sequestration potential for upland soils of Anhui province ranged from 2.77 Tg to 4.08 Tg under realistic scenarios and from 42.8 Tg to 7.17 Tg under ideal scenarios.From Anhui province dryland soil carbon sequestration potential space distribution pattern,larger carbon sequestration potential in huaibei plain region.Popularization of RMPs to the overall upland soils of Anhui province could be considered as an effective strategy to mitigate the rapid raise of the atmospheric CO2 and ensure food security in China.