Effects of Vegetation Restoration Ages on Soil Carbon Pool of Natural Grassland in Loess Hilly Region

[Objective]This Paper aimed to investigate the dynamic variation and distribution of soil carbon of natural grassland under different restoration years in order to understand the dynamic characteristics of soil organic and inorganic carbon pool.[Methods]Using field survey and laboratory analysis method,this study analyzed the dynamic variation of soil total carbon of natural grassland under different restoration years(11,16,22 and 35a)in loess hilly region.[Results]Soil organic carbon(SOC)content in the 0—10cm soil layer surface was increased significantly with the increase of restoration years,while no evident changes were found in the10—100cm soil layer.Variations in average soil organic carbon storage of natural grassland at 0—100cm soil depth decreased initially and then increased with the increase of restoration years.However,it had not reached to the level of farmland.Decalcified phenomenon existed in 0—20cm soil layer.Soil inorganic carbon(SIC)storage was 2.7to 4.5times larger than soil organic carbon storage in 0—100cm total soil layers.No significant variations occurred in total soil carbon storage as the restoration years increased.Soil inorganic carbon storage accounted for about 75.6%to 86.0% of soil total carbon storage in the 0—100cm soil.The SIC pool was an important factor that influenced soil total carbon pool in the study area,which also main-tained the dynamic balance of soil carbon pool in this region.[Conclusion]In the semi-arid environment of the Loess Plateau,soil carbon sequestration effect in natural grassland is not obvious and the improvement of soil carbon pool is likely to require a considerably long period of time.