Response of soil organic carbon density to land-use types and management practices change in agro-pastoral zone

In order to assess variability of soil organic carbon(SOC) across different land-use types and management practices in agro-pastoral zone, two land-use types, permanent grassland and reclaimed cropland in Guyuan County, Hebei province of Northern China, were investigated with SOC density in 0-10, 10-20, 20-30, 30-40, 40-50 cm soil layers and correlations of SOC density with soil bulk density and SOC content as affected by land-use types and management practices change. The results showed that the carbon stored in soils for different land-use types and management practices ranged from 8.21-11.30 kg/m2. The SOC all declined at each successive increment from 0-50 cm depth across the five land-use types and management practices, with the relative distribution greatly skewed towards the top layers. SOC in 0-50 cm soil layers of permanent grassland under different management practices were higher than those in disturbed soils of reclaimed cropland （RC） and fallowing （FC）. For permanent grassland, the management practice of GM has the the highest SOC density in 0-50 cm soil layer, the least SOC density was displayed by FG. For reclaimed grassland, after about 10 years FC, SOC were higher signifcantly in the 0-50 cm soil layer comparing to RC. The results also indicated that land-use types and mangement practices had significantly effect on soil bulk density and SOC content, then on SOC density. GM or grassland enclosure and under controlled grazing therefore was the most feasible and benign short-term grassland management option which could deposit even higher carbon dioxide in agro-pastoral ecotone, Northern China.