Responses of soil aggregate stability, erodibility and nutrient enrichment to simulated extreme heavy rainfall.

Extreme precipitation regime under global change context is estimated to cause heavy rainstorms and longer drought intervals. Temporal variations of soil structure and erosion characteristics during and after heavy rainstorms were less investigated, particularly across a wide soil texture gradient. In this study, 15 soils were selected with clay content ranging in 12.9-38.2%. Soil erosion characteristics and enrichment ratios of organic carbon (EROC) and nitrogen (ERN) were measured during 3 successive rainfall simulations at slope of 15° and intensity of 120 mm h-1. The water-stable aggregate distribution was measured for soils before and after rainfall and drying. The mean weight diameter (MWD) of water-stable aggregate remained unchanged before (1.476 ± 0.182) and after rainfall and drying (1.406 ± 0.135 mm), but decreased for soils with higher organic carbon contents. Soil erodibility (K factor) averaged in 0.018 ± 0.003, 0.011 ± 0.001 and 0.008 ± 0.001 in 3 successive rainfall events, with 42% and 27% decreases after each event, respectively (P < 0.05); and the decreases were greater for less aggregated soils or coarser textured soils. Stepwise regression showed that the <0.25 mm water-stable aggregate explained most variations of K and its dynamics. The EROC and ERN were close to 1 and were not correlated with clay content or MWD (P > 0.05). The ERN decreased first and then remained stable, and EROC was unchanged during successive rainfalls. These results indicated that soil texture or aggregation status affected soil erodibility and its temporal changes in successive rainstorms.