Soil Aggregates of Returning Farmland to Different Bamboo Forests in Southern Sichuan Province | 川南不同退耕还竹林土壤团聚特征比较

chinois. 以川南地区常用的退耕还林竹种撑绿竹和硬头黄竹为研究对象,分析退耕5年、10年和非退耕竹林土壤团聚特征和分形维数,探讨分形维数与土壤基本特性之间的关系。结果表明：与农耕地相比,退耕还竹林地土壤水稳性大团聚体含量明显增加,退耕10年的撑绿竹和硬头黄竹林水稳性团聚体含量最高,分别为农耕地的163.27%和158.36%;平均质量直径（MWD）和几何平均直径（GMD）的变化范围为0.84～2.50mm和1.04～1.98mm,不同土层间MWD和GMD表现一致,均为表层土最高,中层土次之,下层土最低;各土层的微团聚体分形维数为2.308～2.526,且由表层土到中层土呈上升趋势,至下层土无明显变化规律。回归分析表明土壤分形维数与土壤黏粒（〈0.002mm）含量呈极显著正相关关系,与其他粒级含量、土壤密度和土壤有机质含量无显著相关性,因此无法用土壤分形维数来表征该地区土壤密度和有机质含量。研究表明：退耕还竹有利于降低土壤板结,提高土壤大团聚体数量;撑绿竹和硬头黄竹均可以有效降低土壤分形维数,改善土壤通透性,提高土壤结构的稳定性,进而增加土壤的抗侵蚀能力,发挥保持水土作用。

anglais. This study examined the soil aggregate features and fractal dimension （D） of 5-and 10-year de-farmed Bambusa pervariabilis x Dendrocalamopsis daii 3 plantation forests and a Bambusa rigida farmland in southern Sichuan Province, China. The relationships between D and the basic soil properties were also analyzed. Results showed that the bulk density （BD） increased with the increase in soil depth. A sharp increase in water-stable aggregate content between the de-farmed forests and tillage was observed. Both de-farmed for 10 years, B. pervariabilis x D. daii 3 and B. rigida had the maximum water-stable aggregate level, which improved by 63.27% and 58.36%, respectively, compared with tillage. The mean weight diameter ranged from 0. 84 mm to 2.50 ram, whereas the geometric mean diameter ranged from 1.04 mm to 1.98 mm. They also showed the same trend under different plots： surface layers 〉 middle layers 〉 lower layers. The micro-aggregate fractal dimension was 2. 308 to 2. 526, and the D value increased from the surface to the middle layers; however, no significant pattern was observed when the lower layer was reached. Regression analysis indicated a significant positive correlation between D and the clay content, but no relationships were observed between D and the remaining fraction contents such as BD and OM. D could not represent the BD and OM levels in this area. Thus, reversion of farmland to bamboo forest does not only reduce soil compaction but also increases the amount of soil aggregate. Both B. pervariabilis × D. daii 3 and B. rigida can also reduce soil fractal dimension, improve soil permeability, and increase soil structure stability. Thus, the soil anti-erosion ability and soil-water conservation in the study area can be enhanced.