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.%为研究农牧交错区土地利用和管理方式对土壤碳库的影响,以农牧交错区未扰动自然土壤的天然草地和扰动自然土壤的开垦农田为研究对象,测定了不同土地利用和管理方式下 0～50 cm土层的土壤体积质量、土壤有机碳含量及土壤有机碳密度.结果表明,5种土地利用和管理方式下的土壤有机碳密度在8.21～11.30 kg/m2之间,土壤有机碳主要分布在土壤表层,随着土层深度增加,土壤有机碳含量和密度减小.未扰动自然土壤的天然草地,0～50 cm的土壤有机碳含量及碳密度高于扰动自然土壤的开垦农田及撂荒地,以草地围封刈割利用下的土壤有机碳密度最高,草地自由放牧利用下的土壤有机碳密度最低.扰动自然土壤的农田撂荒10a后与开垦农田相比,0～50 cm土层的有机碳含量及碳密度显著提高.土地利用及管理方式的变化改变了土壤体积质最及土壤有机碳含量,进而影响了土壤有机碳密度.围封割草或控制放牧,是适宜农牧交错区增加生态系统土壤碳贮量的利用途径.
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