Effects of wetting rate and simulated rain duration on soil crust formation of red loam

The characteristics of crusts are closely related to soil erosion in red loam under a rainfall condition. To better manage crust-prone soils and to accurately predict hydrological processes, it is necessary to understand the mechanism of crust formation. Wetting rate is an important factor influencing soil aggregate stability and crust formation. In this study, we considered two factors, wetting rate (slow 2 mm h −1 , fast 50 mm h −1 ) and rainfall quantity (intensity of 60 mm h −1 with every 5 min as a treatment from 0 to 60 min). The results show that soil in the fast wetting treatment had higher bulk density, stronger crust strength and lower infiltration rate. Therefore, the fast wetting treatment had higher ability to resist the damage caused by raindrops and to resist soil erosion, and higher runoff rate than slow wetting treatment. Crust formation–destruction–formation process appeared sharp in fast wetting treatment but gentle in slow wetting treatment. Surface morphology and profile microstructure show that crusts were formed earlier in fast wetting treatment. The aggregates in slow wetting treatment had higher stability than those in fast wetting treatment. The crust strength of the soil pretreated by slow wetting was weaker than that in fast wetting case due to the persistent presence of stable aggregates, albeit microaggregates, and, consequently, reduced levels of compaction.