黄土丘陵区土壤团聚体分形特征及其对植被恢复的响应

Fractal dimension of the soil aggregate and its responds to plant rehabilitation in the Hilly-gully region of Loess Plateau

采用计算分形维数的方法，对黄土丘陵区典型草原带土壤团聚体的分形特征及其对植被恢复的响应进行研究。结果表明：1）在植被恢复初期，土壤〉10mm粒级的团聚体含量在0～20和20—40cm层次均较高，含量为331．4～525．6g/kg。随植被恢复年限增加，10—7、7～5、5～3、3～2、2—1mm粒级的团聚体绝对含量下降差异不明显。1～0．5、0．5-0．25和〈0．25mm小粒级土壤团聚体含量，在植被恢复初期（7a）较高。2）随着植被恢复年限增加。土壤〉5mm粒级的水稳性团聚体含量相对下降很快，恢复7a之后，大粒级土壤团聚体表现为上层含量比下层含量低的趋势。相对于干筛结果而言，土壤水稳性团聚体的粒径分布更为均匀、稳定，恢复7a之后的土壤〉0．25mm团聚体含量占到40％～50％，而〉5mm的土壤团聚体则占10％～23％。植被恢复过程中，土壤团聚体由大的团块向小颗粒的土壤团聚体转换，粒径分布更为均匀，土壤结构逐渐改善。3）不同恢复年限土壤团聚体分形维数变化范围为表层2．75～2．86，表下层2．77—2．89，变化范围小，20～40cm土层的分形维数大于0～20cm，恢复植被可使土壤分形维数降低，土壤结构得到改善。

The characteristics of soil aggregates fractal dimension and its responses to vegetation rehabilitation were studied in the Hilly-gully region of Loess Plateau. The results indicated that： 1 ） In the beginning of rehabilitation, the 〉 10 nun soil aggregates were higher both in 0 - 20 cm and 20 - 40 cm, which were between 331.4 - 525.6 g/kg. Along with the increasing of rehabilitation ages, 10 - 7 mm,7 - 5 mm,5 - 3 nun, 3 - 2 mm, 2 - 1 mm soil aggregates declined, the contents of 1 - 0.5 nun, 0.5 - 0.25 nun and 〈 0.25 nun had big changes before and after the 7 year rehabilitation, which were almost double times in the after 7 years rehabilitation. 2） Along with the increasing of rehabilitation years, the soil water stable aggregate which was 〉 5 mm decreased quite fast. After seven years rehabilitation, big grade size aggregates were lower in surface layer than sub-surface layer. Compared to the result of dried sieving way, soil water stable aggregates had more even and stable distribution. Soil aggregates which 〉 0.25 nun was mainly 40% - 50% after 7 years rehabilitation, in total aggregates, but 〉 5 mm soil aggregate was only 10% - 23% approximately. During the process of vegetation rehabilitation, it had the trend that big size soil aggregates converted to small size aggregates, the granule size was more uniformity which showed that good soil structure was formed. 3） The fractal dimension of soil aggregates in different rehabilitation ages were between 2.75 - 2.86 in the surface layer and 2.77 - 2.89 in the subsurface layer, soil fractal dimension was declined along with the rehabilitation years increasing.