Study On High Precision Database And 3D Model Of Soil Organic Carbon Stocks Estimation Of Fujian Province

Accurate estimation of soil organic carbon storage is important to formulate agricultural management measures and simulate global carbon cycle.In this study,taking Fujian Province with rugged terrain in the subtropical region as the study area.Based on the data of attributes collected from sample soil profiles of the second soil survey in 1982 and 1:250,000 digital elevation model（DEM）,a soil database of 1:50,000 was established.This study analyzed the differences of soil organic carbon density（SOCD）and soil organic carbon storage（SOCS）between 2D model（two-dimensional plane area）and 3D model（three-dimensional surface area）,and used the latter to quantify the error size of the former.The results would provide a theoretical basis for the accurate estimation of SOCS in China.The main results were as follows:（1）The results of 2D model and 3D model showed that the total soil areas of Fujian Province were 12.08×10⁴ km² and 12.68×10⁴ km²,respectively.The SOCD in surface layer（0～20 cm）and profile（0～100 cm）were 4.57 kg·m^-2,11.55 kg·m^-2,4.59 kgˉm^-2 and 11.59 kg·m^-2,respectively,and they were higher than the national average level(2.97 kg·m^-2 and 9.13 kg·m^-2).The SOCS in surface layer（0～20 cm）and profile were 552 Tg,1396 Tg,582 Tg and 1470 Tg,respectively,accounting for 2.01%,1.66%,2.12%and 1.74%of the total SOCS in China（27.40 Pg and 84.40 Pg）,respectively.（2）In terms of soil types,the results of 2D model and 3D model showed that the mountain meadow soils with the highest SOCD in surface layer and profile were 7.75 kg·m^-2,29.07 kg·m^-2,7.74 kg·m^-2 and 29.16 kg·m^-2,respectively,and the aeolian soils were the lowest,with 2.87 kg·m^-2,8.21 kg·m^-2,2.87 kg·m^-2 and 8.21 kg·m^-2,respectively.In different cities,the results of 2D model and 3D model showed that the SOCD of Ningde City in surface layer was the highest,with 5.44 kg·m^-2 and 5.45 kg·m^-2,respectively,and the SOCD of Nanping City in profile was the highest,reaching 15.05 kg·m^-2 and 15.09 kg·m^-2,respectively,while Xiamen City was having the lowest SOCD values,with 3.03 kg·m^-2,7.84 kg m^-2,3.05 kg·m^-2 and 7.86 kg m^-2,respectively.In terms of landform types,the results of 2D model and 3D model showed that the mountainous regions with the highest SOCD in sturface layer and profile were 5.28 kg·m^-2,12.85 kg·m^-2,5.29 kg m^-2 and 12.89 kg m^-2,respectively,and the plains were having the smallest SOCD,which were 2.87 kg·m^-2,8.21 kg·m^-2,2.87 kg·m^-2 and 8.21 kg m^-2,respectively.（3）The distribution areas with high SOCD were mainly distributed in the inland areas,especially in the north,northeast and western of Fujian Province,while the distribution areas with low SOCD were mainly distributed in the coastal areas.The SOCD in surface layer was mainly in the range of 2.5～5 kg·m^-2,accounting for 45.27%of the total soil areas.The SOCD in profile was mainly in the range of 5～15 kg·m^-2,which accounted for 60.35%of the total soil areas in Fujian Province.In addition,the SOCD in surface layer and profile generally increased as the rise of altitude,whereas the SOCD slowly decreased with the increase of slope,when the slope was less than 40°,and the SOCD initially increased and then declined when the slope was more than 40°.（4）Compare with the estimation results of 2D model,the relative deviations of the SOCD and SOCS in surface layer and profile of 3D model were 0.34%,0.31%,5.30%and 5.26%,respectively.In terms of soil types,the relative deviations of SOCS in the great group of mountain meadow soils and the subgroup of yellow soils were the highest,reaching 8.84%and 9.27%,9.59%and 9.69%,respectively,and the great group of coastal solonchaks and the subgroup of salted-acid paddy soils were the smallest,which were 0.14%and 0.14%,respectively.In different cities,the relative deviations of SOCS in surface layer and profile of Nanping City and Ningde City were the highest,with 5.95%,5.90%,5.94%and 5.92%,respectively,and Xiamen City was the smallest,which was 3.24%and 2.82%,respectively.In terms of landform types,the relative deviations of soil organic carbon storage in surface layer and profile of the mountain regions were the highest（6.54%and 6.65%）,and the plains were the smallest,which were 1.58%and 1.49%,respectively.In terms of slope grades,when the slope was more than 20°,the differences of the soil distribution areas and the SOCS between 2D model and 3D model were significant and their relative deviations were more than 10%.In the mean time,the accuracy of estimation results using 2D model would be far lower than 3D model,which would produce relatively great error.