中文摘要：

[目的]研究农田土壤有机碳密度特征及区域差异，为区域性土壤生产力培育提供技术参考；为区域性农田土壤碳收集技术选择和配套政策制定提供决策依据。[方法]采用我国第二次土壤普查数据，研究不同用地方式下农田耕层土壤有机碳密度状况。[结果]农田耕层土壤有机碳密度介于0．81—12．68kg·m^-2，平均为3．15kg·m^-2，其中西南区最高，平均达3．63kg·m^-2；华北区最低，平均为3．00kg·m^-2。农田土壤有机碳密度的变异系数为57％，显著比非农业土壤的变异系数低35个百分点。不同用地方式下，水田耕层有机碳密度比旱地的平均高13个百分点，但水田有机碳密度的区域变异显著低于旱地。另外，农田土壤有机碳密度与降水和气温的相关性显著低于非农业土壤，农田中水田土壤有机碳密度与降水和气温的相关性又显著小于旱地。[结论]农田尤其是水田土壤有机碳密度可能更多的是受人为因素影响，人为调控潜力大。

英文摘要：

[Objective ] Study on regional characteristics of soil organic carbon （SOC） density in farmland will not only greatly contribute to technique researches for soil productivity improvement, but also give evidences of technique selection and policy making for carbon sequestration in soils. [Method] Based on the second national soil survey of China, the situation of SOC density in the plow layer of farmland was analyzed under different land use patterns. [Result] SOC density in the plow layer was about 3.15 kg.m2 in average which ranged from 0.81 kg·m^-2 to 12.68 kg·m^-2. The highest density was found in the southeast region with an average of 3.63 kg·m^-2, while the lowest occurred in the northwest region with an average of 3.00 kg·m^-2. The variation coefficient of SOC density in the plow layer of farmland was 57%, which was 35 percentages lower than that of non-farmland soils. Compared to SOC density in the dry land, SOC density in paddy soils was 13 percentages higher with a lower variation coefficient between different regions. In addition, the relationships between the climatic factors （annual average temperature and annual precipitation） and SOC density were lower in farmland than those in non-farmland soils, as well as in paddy soils than those in dry land of farmland. [Conclusion] These results suggest that anthropogenic disturbances have great impacts on SOC density in farmland soils, especially in paddy soils, indicating a high control potential of SOC density.