In order to reveal the role of human activities on soil quality

5 land use patterns were examined

including paddy field

dry land

citrus orchard

artificial forest and natural forest. Each land use pattern was evaluated for its effectiveness at retaining soil aggregate stability and its fractal features in Danjiangkou Reservoir area

in China. The rate of ＞0.25 mm macro-aggregates (R＞0.25)

the percentage of aggregate destruction (PAD)

the mean weight diameter (MWD)

and the geometric mean diameter (GMD ) were tested in this study

and the fractal dimension (D) were also compared. Results showed that the wet sieving method was accurate

reliable and reproducible

and the results based on this method could better reflect the composition and stability of soil aggregate compare to those based on dry sieving method. To some degree

each of aggregate stability indexes could reflect the variation of soil aggregates under different land use patterns. The forests (natural forest and artificial forest) had better soil stability and erosion resistance

with relatively high values of MWD and GMD and relatively low D. However

dry farmland (dry land

and citrus orchard) showed an opposite trend. Its soil stability was weak

the MWD and GMD were relatively low and the D was relatively high. The correlation analysis indicated that aggregate content of each size had significant linear relationship to the indexes of MWD

GMD

and D. And in the transformation of soil aggregate from micro-aggregates (＜0.25 mm) to medium aggregates (0.25—5 mm)

and to large aggregates (＞5 mm)

0.25 mm

1 mm and 5 mm particle size were more critical points.