Fractal dimensions of soil aggregates under different environments in the Loess Plateau

Chinese. 研究不同生境条件下土壤结构体分形维数及其与主要土壤特性的关系。根据植被和土壤类型，从黄土高原不同地域分别采集22个0~20 cm土层土壤样品，利用干筛法测定其结构体组成，分析土壤结构体分形维数及其影响因子。黄土高原22个土壤样品结构体的分形维数为2.267~2.843。土壤类型不同，其土壤结构体的分形维数具有明显的差异，分形维数表现为干润砂质新成土黄土正常新成土简育干润均腐土土垫旱耕人为土。回归分析发现，土壤结构体分形维数与土壤有机质、全氮含量具有极显著的负相关关系，相关系数分别为－0.591 9和－0.640 7(n=22)。对黄土正常新成土，除5~10 mm结构体外，土壤结构体分形维数与各粒径含量均呈现出明显的线性关系，正负相关性以0.25 mm为界，即其分形维数与0.25 mm的结构体含量呈负相关，与0.25 mm的结构体含量呈正相关。多元线性回归分析表明，结构体分形维数与0~0.25，1~2，2~5，5~10 mm结构体含量的偏相关关系达到显著水平，而与0.25~1 mm结构体含量的偏相关系数不显著。在黄土高原地区，土壤结构体分形维数随纬度增加而增加，土垫旱耕人为土结构体分形维数最低，干润砂质新成土结构体分形维数最高，同时土壤结构体的分形也受土地利用方式的影响，分形维数表现为人工林地农地自然林地裸地。_

English. This study is to investigate the fractal dimensions of soil aggregates and their relationship with important soil properties in different environments. In terms of the types of vegetation and soil, 22 soil samples from different profile (0―20 cm, 20―40 cm and 40―60 cm) were collected from different regions in the Loess Plateau. We determined the composition of soil aggregates with dry sieved method, and analysed fractal dimensions of soil aggregates and the effect factors. The results indicated that the fractal dimensions of soil aggregates ranged between 2.267-2.843 for the twenty-two soil samples. Fractal dimensions of soil aggregates were different in various types of soils, Ust-Sandic EntisolsLos-Orthic EntisolsHap-Ustic IsohumisolsEum-Orthic Anthrosols. Regression analysis indicated that there was a highly significant negative correlation between fractal dimension and organic matter and total nitrogen. The correlation coefficient was －0.591 9 for the relationship between fractal dimension and organic matter and －0.640 7 for the relationship between fractal dimension and total nitrogen. In the soils that was classified as Los-Orthic Entisols, having a significant correlation between the fractal dimension and the amount of material in each aggregate size class except for the 5―10 mm aggregate size class. The boundary between positive and negative correlation was 0.25 mm.Fractal dimensions were negatively correlated with the amount of aggregates with diameter 0.25 mm and positively correlated with the amount of aggregates with diameter 0―0.25 mm.Multivariate linear regression analysis indicated a significant partial correlation between the fractal dimension of soil aggregates and the amount of aggregates in the 0―0.25 mm, 1―2 mm, 2―5 mm and 5―10 mm size classes, while the partial correlation coefficient between the fractal dimension of soil aggregates and the amount of aggregates in the 0.25―1 mm size class was not significant. The fractal dimensions of soil aggregates increased with increased latitude on the Loess Plateau.Also, the fractal dimensions largely varied with soil, among which Eum-Orthic Anthrosols was the lowest and Ust-Sandic Entisols was the highest, and it was affected by types of vegetation, which is:artificial woods landfarming landwildwood landbare land._