Research On Spatial-temporal Variability Of Soil Organic Carbon In Typical Cropland Of Henan Province

Carbon sequestration rate in cropland soil is an important index to evaluate the effect and potential capacity of soil carbon sequestration.Accurate estimation of soil organic carbon sequestration rate is very important for studying cropland soil fertility and environmental effect.In this research,typical cropland from Henan Province,was chosen as the study areas.The spatial-temporal variation characteristics and mechanism of organic carbon in cropland were systematically revealed from point to surface scale.Field experiments were carried out in two typical middle and low yield fields,fluvo-aquic soil(2010-2018)and Shajiang black soil(2012-2016),respectively.The treatments of no fertilization,conventional chemical fertilization,conventional chemical fertilization + straw returning,conventional chemical fertilization + straw returning + organic fertilizer,conventional chemical fertilization + organic fertilizer treatments were designed to reveal the mechanism of changes in soil organic carbon budget and expenditure.Taking Fengqiu County,Yuzhou County,Fangcheng County and Huangchuan County in Henan Province as typical counties,the physical and chemical properties and farming conditions of farmland soil in the county were investigated and analyzed in 2011.The spatial-temporal variation characteristics and vital influencing factors of farmland organic carbon in the province were analyzed with reference to the Second National Soil Survey data.Based on this results,Fengqiu County was selected as a special case.By integrating measured data,TM image spectral data and DNDC model simulation data,the spatial-temporal variation characteristics of soil organic carbon density under four scenarios of no fertilization,single chemical fertilizer,single chemical fertilizer + straw returning,single chemical fertilizer + straw returning + organic fertilizer were simulated,and the change trend of soil organic carbon density in farmland under different scenarios were also quantitatively analyzed.Based on the above analysis results,the mechanism and spatialtemporal variability of soil organic carbon change in farmland were systematic revealed.In the present research,a multi-source data analysis method was used to analyze the spatial-temporal variability of soil organic carbon in farmland.The purpose of this study is to provide a theoretical basis for the study of spatial-temporal variability and estimation methods of soil organic carbon,and the main results were as following:(1)The field test results shown that the effect of different farmland management measures on variation of soil organic carbon was significant.That is,single application of chemical fertilizer can hardly stabilize and fix more soil organic carbon.Straw returning and organic fertilizer application can significantly improve carbon sequestration ability and carbon sequestration rate.Organic manure can significantly increase the content of organic carbon in Shajiang black soil,stabilize water-stable aggregates and enhance soil carbon sequestration capacity.The survey results of typical counties in Henan province also shown that the overall carbon sequestration rate of farmland soil in Henan Province was remarkable since the 1980 s.The carbon sequestration rate in some areas was as high as 0.3-0.5 t C/ha,while in a few areas it was 0-0.2 t C/ha.Only a few areas showed carbon loss,and the study area still had great carbon sequestration potential in the future.Moreover,straw returning was widely used in the study area,and 750 kg/ha/yr was used as annual fertilizer input.The results also showed that soil bulk density,pH,straw returning and fertilization were the key factors affecting soil carbon sequestration rate.(2)Based on multi-source data,the results of simulation analysis shown that the situational conditions of fertilization(F0)and fertilizer application(FR)were difficult to maintain the background carbon of surface soil,and shown as carbon source.Soil organic carbon density increased significantly year by year,carbon storage also showed a linear upward trend,and carbon sink effect was significant in straw returning(FRS)and substituting manure for fertilizer by 20%(FRSM)treatments on the basis of conventional fertilizer application alone.(3)Through the discussion and analysis of the estimation results,a method based on multi-source data is proposed to estimate the spatial and temporal variation characteristics of soil organic carbon and carbon storage in farmland surface.The estimation results of carbon reserves are consistent with the measured results,and have certain technical advantages,such as low cost and simplicity of operation.And this method has a certain potential value in large-scale acquisition of spatial and temporal variation of soil carbon in farmland.