采用时空互代法，以不同年限坡改梯田为研究对象，分析了陇东黄土丘陵区梯田土壤有机碳（SOC）的时空分布特征。结果表明，1）陇东黄土丘陵区黄绵土在坡改梯后近50 a内，农田0—60 cm土层土壤有机碳处于持续累积状态，20—40 cm与40—60 cm土层SOC较坡耕地的增幅分别为54.6%和52.4%，大于表层增幅 （33.7%）（P〈0.05）；各土层SOC随梯田年限的变化趋势基本一致，在修建初期（0~8 a）累积较快并超过坡耕地SOC水平（P〈0.01），24 a 后有了显著提高（P〈0.05），后期SOC累积变化不显著。2）不同土壤类型及地形下SOC含量及累积速率有所差异，0—20 cm 土层的SOC在黄绵土中累积最为明显，20—40 cm与40—60 cm 两个土层SOC在红粘土中的累积量最为显著（P〈0.05）；阴坡表层SOC大于阳坡，梯田修建25 a 后阴坡平均SOC较阳坡高22.1%。3）梯田土壤有机碳的时空变异受土壤类型的影响最大，其贡献率达62.0%，海拔和坡向影响次之，两者可解释20.4%的有机碳的变异；梯田年限和施用有机肥可分别解释11.7%和5.8%的变异。陇东黄土丘陵区坡改梯田土壤在当前经营状况下表现出较弱的碳汇效应。
Wind and water erosion are among the most important causes of soil loss, and understanding their interactions is important for estimating soil quality and environmental impacts in regions where both types of erosion occur. We used a wind tunnel and simulated rainfall to study sediment yield, particle-size distribution and the fractal dimension of the sediment particles under wind and water erosion. The experiment was conducted with wind ero- sion firstly and water erosion thereafter, under three wind speeds （0, 11 and 14 m/s） and three rainfall intensities （60, 80 and 100 ram/h）. The results showed that the sediment yield was positively correlated with wind speed and rain- fall intensity （P〈0.01）. Wind erosion exacerbated water erosion and increased sediment yield by 7.25%-38.97% relative to the absence of wind erosion. Wind erosion changed the sediment particle distribution by influencing the micro-topography of the sloping land surface. The clay, silt and sand contents of eroded sediment were also posi- tively correlated with wind speed and rainfall intensity （P〈0.01）. Wind erosion increased clay and silt contents by 0.35%-19.60% and 5.80%-21.10%, respectively, and decreased sand content by 2.40%-8.33%, relative to the absence of wind erosion. The effect of wind erosion on sediment particles became weaker with increasing rainfall intensities, which was consistent with the variation in sediment yield. However, particle-size distribution was not closely correlated with sediment yield （P〉0.05）. The fractal dimension of the sediment particles was significantly different under different intensities of water erosion （P〈0.05）, but no significant difference was found under wind and water erosion. The findings reported in this study implicated that both water and wind erosion should be controlled to reduce their intensifying effects, and the controlling of wind erosion could significantly reduce water erosion in this wind-water erosion crisscross region.
