中文摘要：

利用中国第2次土壤普查数据，分析了稻作和旱作方式下农田耕层土壤有机碳和全氮特征及其区域差异。结果表明，水田土壤有机碳和全氮含量分别为旱地的147．8％和145．5％，但水田碳氮含量的区域变异低于旱地。全国水田和旱地土壤有机碳氮比值分别为10．8和9．9，各区域水田土壤碳氮比值普遍高于旱地，其中东北水田最高，而华东旱地和西北旱地最低。旱地碳氮比值的区域变异显著，水田则不显著。农田耕层土壤有机碳和全氮含量呈显著正相关，除华北地区外，各区域无论水田还是旱地其碳氮含量之间相关系数都超过0．8，达极显著水平。由此可见，我国农田耕层土壤有机碳和全氮含量之间存在显著耦合关系，而且不同利用方式和区域之间差异显著；相同氮水平下，水田土壤可能储存更多的有机碳。

英文摘要：

Based on the data of the second national soil survey in China, coupling characteristics and spatial variation of soil organic carbon （SOC） and total nitrogen （TN） in the plow layers of paddy and upland fields were studied. Results show that SOC and TN contents were higher in paddy fields than in upland fields by 47.8% and 45.5%, respectively, but spatial variation of SOC and TN were found higher in upland than in paddy fields. Soil organic carbon and total nitrogen ratio （C/N） was about 10.8 in paddy fields,higher than 9.9 in upland fields. The highest C/N ratio value was found in the paddy fields in Northeast China while the lowest in the upland fields in Northwest China and East China. Meanwhile, results also show significant regional variation of C/N ratio in upland fields, but little significant variation in paddy fields. Correlation analysis shows that SOC was significantly and positively correlated with TN, with correlation coefficients being all higher than 0.8 in paddy and upland fields except for in North China. Moreover,the correlation coefficients may decrease along with the length of agricultural land use. The findings above indicate that there exist close coupled relationship between SOC and TN and distinct regional variation in the plow layer of farmland under different land use patterns. To understand these coupled characteristics will greatly contribute to improvement of regional farmland productivity and agro-ecosystem environment,and as reference to the technique selection and policy making for carbon sequestration in farmland soils in China.