*3.1. Infiltration Rates of Bare Black Soil Under Various Rainfall Events*

The average values of two repeated trials were used for the infiltration rate curves for different rainfall intensities and soil moistures of the black soil (Figure 3). The initial infiltration rates were equal to the rainfall intensities before ponding. When the water ponded on the surface, infiltration occurred at the potential infiltration rate and runoff generation began. The times to runoff in the dry runs were around 48.0, 16.0, 7.4, and 5.1 min, and the total infiltration amounts were 27.67, 38.30, 45.14, and 47.54 mm under the four rainfall intensities, respectively. The higher the rainfall intensities were, the earlier the runoff began. Then, infiltration rates decreased and tended to become steady as the rainfall continued due to the soil crust that formed on the soil surface. The final infiltration rates of the dry runs were 0.37, 0.40, 0.53, and 0.54 mm/min. In contrast, the runoff times of the wet runs were within 5 min and the infiltration rate became stable soon after runoff generation under various rainfall intensities. The final infiltration rates corresponding to the rainfall intensities were 0.21, 0.23, 0.43, and 0.51 mm/min, respectively. The total infiltration amounts were 44.43, 55.05, 72.81, and 80.18 mm under the four rainfall intensities.

**Figure 3.** Infiltration rates under various rainfall events.
