3　Conclusions

Soil crusting and erosion result from aggregate breakdown and detachment of soil fragments by rain.Thus,the susceptibility of soil is often predicted from aggregate stability measurements.Previous studies focused on the measurement of aggregate water stability because of the similar conditions of aggregate breakdown.Numerous methods have been developed to assess aggregate stability.However,most of these methods cannot express aggregate water stability in a quantifiable manner,thereby limiting applications in other research areas.

Mechanical properties are quantitative indexes of soil structure.In this study,the relationships of aggregate breakdown and soil detachment were compared under simulated rainfall with aggregate mechanical stability(penetration resistance and TS)and water stability.Aggregate water stability and mechanical stability(TS and penetration resistance of dry aggregates)showed good relationships with aggregate breakdown.The MWD of the wet sieving method and TS were the best indexes for estimating fragment size distribution and splash detachment.The MWD of the wet sieving method contributed to the prediction of fragment size distribution after rainfall,whereas TS contributed to the prediction of splash detachment.

Tensile strength can be used to determine the critical pressure or energy of aggregate breakdown compared with the wet sieving method and is a sensitive indicator of soil structure in soil tillage.Tensile strength can be determined using simple procedures and devices as well as aggregates of varying sizes.Tensile strength correlated with soil clay and oxides.Thus,TS is a good index of fragment size distribution and splash detachment.The development of a simpler and more rapid method to estimate the stability of soil to erosion using TS as an index is possible.