黄土丘陵区不同土地利用方式土壤团粒结构分形特征

Fractal features of soil aggregate structure under different land use in the Hilly-gully region of Loess Plateau

土壤团粒、水稳性团粒和微团粒状况是影响土壤结构和性质的重要因素。运用分形理论研究黄土丘陵区纸坊沟流域7种不同土地利用方式土壤团粒结构的分形特征。结果表明：表层土壤团粒的分形维数在1．641—2．114之间，其大小顺序为人工草地〉果园〉坡耕地〉乔木林地〉灌丛〉天然草地〉人工梯田。土壤水稳性团粒的分形维数在1．774～2．384之间，其变化顺序为果园〉乔木林地〉人工草地〉坡耕地〉天然草地〉人工梯田〉灌丛，二者均表现出≥0．25mm粒级土壤团粒含量越低，分形维数越高的规律；分形维数与≥5mm、5～2mm和≥0．25mm粒级的土壤团粒、水稳性团粒呈极显著负相关（P〈0．01），与〈0．25mm粒级的呈极显著正相关（P〈0．01）；结合团粒结构体破坏率可知，灌丛土壤结构与稳定性最好，其次为天然草地，人工草地最差；表层土壤微团粒结构分形维数在2．360～2．487之间，大小顺序为天然草地〉乔木林地〉坡耕地〉人工梯田〉人工草地〉果园〉灌丛，灌丛有助于促进土壤微结构形成，分形维数与0．25-0．05mm和〉0．001mm粒级土壤微团粒含量呈极显著负相关（P〈0．01），与〈0．001mm粒级土壤微团粒含量呈极显著正相关（P〈0．01）；下层土壤质地主要与成土母质有关，人为干扰小，3种分形维数间存在显著正相关水平（P〈0．05），土壤有机质含量与3种分形维数显著负相关（P〈0．05）。土壤团粒结构分形特征可作为土壤评价指标之一，分形理论为土壤结构、性质和评价研究提供了新方法。

The status of soil aggregates, water stable aggregates and microaggregates are important factors affecting soil structures and features. Based on the fractal theory, the fractal dimension of soil aggregates and microaggregates structure under seven different land use types in Zhifang Hilly-gully region was studied. The results showed that ： the fractal dimension of the upper layer （0 to 20 cm） soil aggregate structure under these seven land use types ranged from 1. 641 to 2.114. The fractal dimension of soil aggregate of artificial meadow was highest, followed by orchard, slope crop-land, arbor forest land, shrub land, natural meadow and artificial terrace. The fractal dimension of water stable soil aggregate ranged from 1. 744 to 2. 384, the fractal dimension of orchard water stable soil aggregate of artificial meadow was highest, followed by arbor forest land, artificial meadow, slope crop-land, natural meadow, artificial terrace and shrub land. Both of the conditions showed the same law： The lower total amount of the soil aggregates （more than 0.25 mm） was, the higher fractal dimension was. There were remarkable negative correlation between the fractal dimension and not less than 5 mm, 5 to 2 mm and not less than O. 25 mm soil aggregates and water stable aggregates contents. But significant positive correlation with less than 0.25 mm soil aggregates. Considered the rate of soil structural damage, the soil structure and stability of shrub land was the highest, the next was natural meadow, artificial meadow was the lowest among these seven land use types. In the upper soil layer （0 to 20 cm） the range of fractal dimension of soil microaggregate was 2. 360 to 2. 487. The fractal dimension of soil microaggregate of natural meadow was highest, followed by arbor forest land, slope crop-land, artificial terrace, artificial meadow, orchard, and shrub land was the lowest of that. It was showed that shrub land and natural meadow were beneficial to forming soil microaggregates. The correlation analysis results showed that fractal dimension had remarkable negative correlation with 0.25 to 0.05 mm and more than 0.001 mm microaggregates, also had positive correlation with less than 0.001 mm microaggates. But the soil texture of lower layers （20 to 60 cm） were relevant to the parent material and little affected by human beings activities. There existed significant positive correlation among three fractal dimensions （ P 〈 0.05 ）, also had negative correlation between soil organic matter and fractal dimensions （ P 〈 0.05）. The fractal dimension could be one of the indices of soil quantity evaluation. The fractal theory was also considered as a new tool to research on the soil structure and features.