土地利用方式对紫色土丘陵区土壤剖面碳、氮影响

Effect of land use change on soil organic carbon and total nitrogen in soil profiles located in Purple Hilly Areas

采取野外调查与室内分析相结合的方法研究了紫色土丘陵区林地、撂荒地、水田、旱地土壤剖面(0～40cm)有机碳、全氮变化特征。结果表明,有机碳、全氮均随土层深度增加而逐渐减小,且林地、撂荒地有机碳递减幅度高于水田、旱地。相对于撂荒地和旱地,水田、林地更利于有机碳、全氮的积累。林地有机碳和全氮在0～5cm土层表现出绝对优势;随土层递增,与水田、撂荒地和旱地的差异逐渐减小。水田有机碳和全氮在大于10cm土层显示最大值,而撂荒地有机碳和全氮仅在土壤表层高于旱地。有机碳与全氮存在显著正相关关系;w(C)/w(N)随土层深度增加而降低,且林地、撂荒地降低幅度较大,因此相对于水田、旱地,林地和撂荒地w(C)/w(N)仅在0～10cm显示较大值。可见,土地利用方式对陆地生态系统碳、氮蓄积有明显影响,通过旱地还林或撂荒可以增加土壤特别是表层土壤对碳、氮的积累。

Soil organic carbon （SOC） and total nitrogen （TN） in soil profiles of woodland, wasteland, paddy field and dryland located in purple hilly areas were studied with field survey and laboratory analysis. Results showed that the contents of SOC and TN decreased with the increasing of soil depth, and the deceasing extent in woodland and wasteland were higher than that of paddy field and dryland. Compared with wasteland and dryland, paddy field and woodland were more conducive to the accumulation of organic carbon and nitrogen. The contents of SOC and TN in the 0-5 cm layer of woodland displayed obviously higher than paddy field, wasteland and dryland. With the increasing of soil depth, the difference of SOC and TN contents between woodland and other land use types decreased gradually. The contents of SOC and TN in paddy field were the highest in the soil depth of 10-20 cm .Compared with dryland, wasteland was favorable to accumulate soil organic carbon and nitrogen in soil surface layer. Soil organic carbon had a significantly positive correlation with nitrogen. The C/N ratio decreased with the increasing of soil depth, and decreased more rapidly in woodland and wasteland. Therefore, the C/N ratio in woodland and wasteland had a higher value in the 0-10cm soil layer when compared to paddy field and dryland. These showed that land use had a significantly effect on the accumulating of carbon and nitrogen in land ecosystem, and the conversion of dryland into woodland or wasteland could increase the accumulation of carbon and nitrogen in soil, especially in soil surface layer.