土壤有机碳(SOC)是近年来全球变化研究的热点之一,表层(0~20cm)和1m土体的SOC是评估农田SOC的两个重要指标[1]。很多研究利用第二次土壤普查资料来估算农田SOC[2-6],一些研究已表明近20年来我国耕作土壤,尤其是表层(一般为0~20cm)的SOC基本呈增加的趋势[5-8],这与秸秆还田、有机肥与化肥合理施用以及少(免)耕技术推广有关[9-10]。但由于农田SOC,至少是表层SOC,是 Soil organic carbon (SOC) is one of the hotspots in global change research in recent years. The surface SOC (0 ~ 20cm) and SOC of 1m soil are two important indexes to evaluate farmland SOC [1]. Numerous studies have used the second soil census data to estimate farmland SOC [2-6]. Some studies have shown that the SOC of cultivated soils in our country, especially the surface layer (generally 0-20 cm), has been increasing basically in the recent 20 years [5- 8], which is related to the straw returning, the rational application of organic fertilizer and chemical fertilizer and the promotion of less (free) farming technology [9-10]. However, due to farmland SOC, at least the surface SOC, is