Effects Of Scale On Estimation Of Soil Organic Carbon Storage In Fu Jian Province

Soil organic carbon（SOC）has an important position in the global Carbon cycle,and its minor changes will have a significant impact on global climate.With the development of computer technology,the method of estimating organic carbon reserve based on soil map and various attribute data is becoming more common,but for now many studies used a single mapping scale soil database in the estimation of soil organic carbon storage in national and regional and did not concerned series scale in the estimation of soil organic carbon storage.this study with the fujian province as an example,analyze the influence of the 6kinds of resolution mapping scale soil databases（county level of 1:50,000 district level of1:200,000 province level of 1:500,000 and nation level of 1:1,000,000,1:4,000,000,1:10,000,000）commonly used in China four administrative levels on the estimation of organic carbon reserves,clarify the uncertainty caused by different mapping scales,and reveal the reasons for their internal differences.The main results are as follows:（1）The soil surface（0-20 cm）and profile（0-100 cm）of organic carbon reserves in Fujian province were estimated at the 6 mapping scales of 1:50,000-1:10,000,000,respectively.Results show that based on the mapping scale that SOC density in the surface soil layer（0-20cm）was estimated at 4.57 kg·m^-2,5.28 kg·m^-2,4.80 kg·m^-2,4.53 kg·m^-2,5.15kg·m^-2,4.75 kg·m^-22 and SOC reserves at 552 Tg,637 Tg,573 Tg,573 Tg,614 Tg,549 Tg,respectively.In the soil profile（0-100 cm）SOC density was estimated at 11.55 kg·m^-2,12.46kg·m^-2,11.07 kg·m^-2,11.52 kg·m^-2,12.65 kg·m^-2,12.71 kg·m^-2,and SOC reserves at 1,396 Tg,1,502 Tg,1,321 Tg,1,395 Tg,1,508 Tg,1,532 Tg,respectively.Under the most detailed mapping scale of 1:50,000 soil organic carbon density is higher than the national average level(2.97 kg·m^-22 and 9.13 kg·m^-2).Soil organic carbon reserves account for 2.01%and1.66%of the national surface and profile respectively.T square test showed that the estimation results of most soil cartographic scale were significantly different from the1:50,000 scale in the most detailed data（p<0.001）.In general,regarding Fujian Province as a whole,the estimation of SOC density and storage in the surface soil layer and profile based on the soil map 1:1,000,000 in scale deviated the least from the currently available most detailed large-region data,1:50,000 in scale,being 0.67%and 0.82%respectively,while that based on the soil map 1:200,000 in scale did more,reaching 15.57%and 15.34%respectively,this is partly a testament to the reliability of the current national scale of 1:1,000,000 soil databases.（2）From the perspective of different soil types,the highest SOC densities were found in the surface soil layer and profile of mountain meadow soil and mountain meadow subgroups at the 1:50,000 mapping scale,which were 7.75 kg m^-22 and 29.07 kg m^-2,7.74 kg m^-22 and 29.16 kg m^-2,the aeolian soil and coastal aeolian soil subgroups had the lowest densities,0.94 kg m^-22 and 2.17 kg m^-2,0.94 kg m^-22 and 2.17 kg m^-2,respectively.In the different mapping scales,the skeleton soil and subclass of skeleton soil,among all the types of soils,was most affected by mapping scale,with relative deviation of SOC reserves and densities in the surface soil layer and soil profile being 88.75×10⁴%,81.96×10⁴%and273.24%,241.93%,respectively.However,The relative deviation of SOC density in the surface soil layer of red soil,the largest land area in Fujian Province,is the smallest under the surface soil 1:1,000,000 scale,which is 4.28%,the lowest under the profile soil is 1:500,000,only 1.53%,and the relative deviation of SOC density in the surface soil layer of red soil,is the smallest under the surface soil 1:1,000,000 scale,which is 0.14%,the lowest under the profile soil is 1:500,000,only 0.72%.（3）In terms of administrative region,the soil surface and the soil profile of Nanping and Longyan were the highest,5.41 kg·m^-22 and 15.05 kg·m^-2,5.44 kg·m^-22 and 12.28 kg·m^-2respectively,the soil surface and the soil profile of Xiamen was lowest,3.05 kg·m^-22 and 7.86kg·m^-2.The SOCD in the soil surface and the soil profile influenced by mapping scale was Fuzhou city.Compare with 1:50,000 mapping scale,in 1:4,000,000 mapping scale that the relative deviation highest were 33.99%and 40.14%.The SOCD and SOCS in the soil surface influenced lowest by mapping scale was Quzhou city.The SOCD and SOCS in the soil profile influenced lowest by mapping scale was Longyan city.All the findings in the study demonstrate that mapping scales does have certain influences on estimation of SOCS in the soils of the same area.In the case that administrators of an area do not have any accurate soil databases,it is advisable for them to estimate SOCS in their region and design agricultural management measures.