Abstract: 【Objective】The objective of this research was to study the purple soil aggregate stability compared with soil erosion in different land use types of dry land.【Method】By using the methods of Simulated Rainfall and analysis characteristics of soil aggregates, the purple soil aggregate stability characteristics of four land use types and their impacts on the process of erosion were studied.【Result】It was found that fast wetting made the majority of aggregate breaking down to the small aggregates. The great impact of two treatments which were slow wetting and wet stirring was the 5-2 mm large aggregates which the diameter is mainly concentrated in 2-0.5 mm after collapse. The aggregate stability of four land types is mulberry plantation＞alfalfa＞grassland＞vegetable garden. Both the MWD and GMD are the smallest for four land use types of fast wetting, and the largest of the MWD and GMD are slow wetting. The mainly collapse mechanism of soil aggregates in purple soil dry land is fast wetting when the internal air pressure, and the minimal damage is clay swelling. The order of total runoff and sediment in four land use types under simulated rainfall is vegetable land＞grassland＞alfalfa＞mulberry plantation, and the process of runoff and sediment coupled with the aggregate characteristics of stability. The correlation of soil aggregate stability index between runoff rate and sediment yield rate of rainfall is high in the first 1 hour.
MWD values under fast wetting were significantly negatively correlated with runoff and sediment erosion. The mainly soil erosion of aggregate crushing mechanism of purple soil in dry land is soil aggregate destruction of the internal air pressure.【Conclusion】The worse the stability of soil aggregates, the more erosion and runoff in purple soil dry land. The relation between soil aggregate stability and sediment characteristics is the highest in antecedent rainfall erosion. It is better to use MWD to reflect the relationship between purple soil aggregates stability and erosion and runoff. The mainly soil erosion of aggregate crushing mechanism of purple soil in dry land is soil aggregate destruction of the internal air pressure.

Key words: Aggregate stability, Erosion process, Dry land, Purple soil