Study on, fractal features of soil microaggregates during different restoration stages in the loess hilly region

Chinese. 运用分形理论研究黄土丘陵区不同恢复年限草地土壤微团粒的粒径组成、分形维数特征及与土壤理化性质关系，使分形学在土壤微团粒性状与土壤肥力特征研究中得到进一步应用，并为评价草地生态系统土壤特征及生态恢复提供新方法。结果表明：表土层分形维数随植被恢复年限的增加而减少；剖面土壤沙粒含量越高，微团粒分形维数越低，粘粒规律相反，而粉粒与分形维数相关性不显著；土壤质地由粗到细使得分形维数由小到大变化；分形维数也可有效地表征不同植被恢复年限的草地土壤结构和养分的变化趋势；分形维数与土壤容重、非活性孔度、全磷、速效钾及氨态氮之间存在正相关性，与土壤活性孔度、孔隙比、有机质、全氮、碱解氮及硝态氮表现出负相关。

English. The composition of soil microaggregate and condition of soil structure are important factors to affect soil character and fertility and soil microaggregate in different restoration year have different fractal di mension feature. The particle size component and fractal dimension of soil microaggregats as well as the relationship between fractal dimension and soil physical and chemical characters were studied using fractal di- mension theory under different restoration stages of grasslands in the Hilly Loess Region. The objective of this study was to apply the fractal dimension theory to soil microaggregate and soil nutrient investigation and supply a new tool for grassland ecosystem evaluation. The results show that the longer the restoration time, the less the fractal dimension of soil microaggragates in the upper layer; the higher the sand content, the higher the fractal dimension; however, the clay content had an opposite trend and the silt content had no significant correlation with the fractal dimension. The fractal dimension could effectively represent the trends of soil texture and soil nutrients under different restoration stages. Positive correlation existed between fractal dimension and bulk density, non-capillary porosity, porosity ratio, total phosphorus, available potassium, and ammoniac nitrogen, while fractal dimension had negative correlation with capillary porosity, soil organic matter, total nitrogen, available nitrogen, and nitrate nitrogen. The research suggests that the fractal dimension of soil microaggregats could be a comprehension index of soil quantity evaluation.