Correlations of soil nutrients and fractal dimension features of soil aggregates in different forestland in loess region of western Shanxi Province, northern China

In this study, taking locust forest, Pinus tabuliformis forest, Cornus officinalis forest and secondary forest as research objects, which were planted in the returning farmland to forestland, and taking the abandoned land, farmland as control group, all the classes from 0 -10 cm, 10 -20 cm, 20 -30 cm of soil aggregate size were measured and classified by using Microtrace S3500 laser particle size analyzer, the fractal features of soil aggregate were analyzed by using the fractal geometry method. And the content of total N, total K in soil from different forest was determined to explore the relationship between fractal dimension of soil aggregates and soil nutrient so as to provide theoretical basis for returning farmland ecological benefit evaluation, and it will provide application values. The results showed that the soil aggregate fractal dimensions varied from 2.22 to 2.60, the average number was 2.44; soil aggregate fractal dimension of P. tabuliformis forest and R. pseudoacacia forest increased with soil depth increased, but agricultural land and secondary forest soil aggregate fractal dimension didn't change significantly, and the D value of soil aggregate fractal dimension of C. officinalis forest decreased with soil depth increasing; there were significantly positive correlations between aggregate volume fraction of 10 -50m and the fractal dimension of soil aggregates, soil aggregate size showed a negative correlation with the former; there was a lower content of organic matter, total P, total K in abandoned land soil, which was poor by fertility and texture, but the soil fertility and texture condition was completely opposite in C. officinalis forest, it showed significant improvement effect to return farmland to forestland.