摘 要 ：通过对甘肃省庄浪县梯田土壤采样分析，结合第二次土壤普查及庄浪县耕地质量评价数据，估算梯田土壤固碳速率并分析其影响因素。结果表明: 1）该县农田土壤沟谷台地的有机碳含量最高，沟谷、 梁峁坡地次之，沟谷川坪地有机碳最低，不同地形有机碳含量差异显著（P<0.05）; 2）80% 的样点土壤有机碳含量在6.0~11.0 g/kg之间，总体上0—20 cm农田土壤有机碳含量呈现正态分布，剖面有机碳含量从上至下呈逐渐递减规律; 3）现阶段庄浪县0—20 cm农田土壤有机碳密度为20.02 t/hm2，低于全国耕层土壤有机碳密度平均水平（33.45 t/hm2），近30年0—20 cm 土壤固碳速率为C 63 kg /(hm2·a)，近5年固碳速率为 C 26 kg /(hm2·a); 4）在半干旱区县域尺度上，地形部位可解释43%的有机碳变异性，有机肥、 坡向和田面坡度三者之和可解释47.1% 的有机碳变异性，土壤类型可解释9.9% 的有机碳变异性。综合分析表明，庄浪县农田土壤有机碳密度在过去30年间呈增加趋势，可能与庄浪县在60年代开始的大规模梯田建设和水土流失治理有关。
Abstract:To estimate the soil carbon sequestration rate and its influencing factors at a county level, we selected Zhuanglang County in southern Gansu Province as the study area. Soil organic carbon sequestration rates were calculated by using some of the results of the second national soil survey and as well as the data of farmland quality evaluation in Zhuanglang County. Farmland soil samples were collected and analyzed in July 2011 The results show that the soil organic carbon contents of the county’s farmlands in the valley terraces are the highest, followed by the lands located in valleys and mountain ridge slopes, and the organic carbon contents in flat lands in the valleys are the lowest. Significant differences are found in organic carbon contents in different terrains (P<0.05). The soil organic carbon contents in 80% of the sampling sites are in the range of 6.0-11.0 g/kg, and the organic carbon contents in 0-20 cm soils present a normal distribution. The organic carbon contents in soil profiles show a decrease trend from top to bottom. The organic carbon density in 0-20 cm soils of the study area is 20.02 t/ha, which is below the average level of the country (33.45 t/ha). The carbon sequestration rate in 0-20 cm soils in the past 30 years is C 63 kg/(ha·a), while it is C 26 kg/(ha·a) in the past five years. At the county level in the semiarid region, the topographic position can explain 43% of organic carbon variability, the organic fertilization, aspect and field surface slope can explain 47.1% of the organic carbon variability, and the soil type can explain 9.9% of organic carbon variability. The results of the comprehensive analysis show that the farmland soil organic carbon density of Zhuanglang County in the past 30 years is increased, and this probably relies on the terrace construction and soil and water conservation. Further study should be conducted on the impact of the terrace construction and fertilizer inputs on soil organic carbon density and carbon sequestration rate in the farmlands.