为更好地了解耕作侵蚀对坡耕地土壤碳循环的影响,采用~(137)Cs示踪技术研究了川北山区坡耕地土壤再分配对土壤有机碳和团聚体有机碳含量与储量的影响。结果表明:与该区土壤~(137)Cs有效背景值比较,短坡耕地上坡部位(坡顶、坡肩)土壤中~(137)Cs含量降低了76.91%,而下坡部位(坡脚、坡趾)增加了24.02%;坡耕地上坡部位发生土壤损失,耕作侵蚀平均速率为63.22 t/(hm~2?a),占土壤总侵蚀的94.61%,耕作导致下坡土壤沉积,平均沉积速率为23.94 t/(hm~2?a)。上坡土壤中大于2 000 mum、250~2 000 mum和53~250 mum的团聚体所占比例显著低于下坡,而小于53 mum的团聚体所占比例则相反;土壤及不同粒级团聚体的有机碳含量与储量下坡显著高于上坡。土壤和不同粒级团聚体的有机碳含量与~(137) Cs面积浓度呈极显著正相关关系,说明侵蚀引起土壤再分配造成上坡有机碳含量贫瘠,而下坡相对富集。因此,川北山区坡耕地施肥管理应关注土壤质量空间变异特征。

In order to better understand the effects of tillage erosion on carbon cycle in the sloping farmland, responses of soil organic carbon and aggregate associated carbon to soil erosion were explored in a mountainous region of northern Sichuan Basin, southwest China, with ~(137)Cs tracer and laboratory analysis method. The results showed soil loss was found in upslope where ~(137)Cs concentrations were lower (soil erosion rates were greater), whereas soil deposit occurred in the bottom of sloping farmland where ~(137)Cs concentrations were higher (soil erosion rates were less). Not only water erosion but also tillage erosion contributed to soil losses. Tillage erosion played an important role in sloping farmland soil redistribution, average tillage erosion rate in upslope was 63.22 t/(hm~2?a), occupying 94.61% of total soil erosion. Soil deposit rate was 23.94 t/(hm~2?a)in low positions. Soil erosion resulted in the lowest >2 000 mum, 250~2 000 mum and 53~250 mum size aggregates, and created the highest <53 mum aggregate fraction in upslope. Meanwhile, soil organic carbon and aggregate associated carbon content and stock were significantly lower in upslope positions than these in bottom slope positions. There was significant correlation between soil organic carbon, content of aggregate associated carbon and ~(137)Cs inventory, suggesting that soils were more fertile in bottom positions than in top positions due to soil redistribution by soil erosion. Therefore, fertilization management strategies should involve spatial variation of soil properties in purple soil of hilly sloping farmland.