5　Conclusion

Due to different parentmaterials,the percentages of all five size fractions(＞5mm,5～2mm,2～1mm,1～0.5mm,and 0.5～0.25mm)of the macro-aggregates from Quaternary red clay were higher than those from Shale,and the particle size distribution of the micro-aggregates was significantly different.The stability of the macro-and micro-aggregates from Quaternary red clay was stronger than that from the Shale.Regardless of the soil parent materials,the water stability of surface cropland soil macro-aggregates was significantly lower than that in other land-use types.For micro-aggregate stability,there was no significant regularity among land-use types.

Ald was the most prominent aggregating agent for macroaggregates,and clay was superior in binding the micro-aggregates.The contribution of the Feo to macro-and micro-aggregate stability was the weakest,suggested by VIP values and regression coefficients from PLSR models.The role of SOM in the aggregation of these soils was also not clear,and this could be due to low content in these soils.Our results indicated that the clay,Fed,Ald,and Alo were effective aggregating agents and contributed significantly to macro-and micro-aggregate stability.