3.2 Soil aggregate fragments characteristic parameters
As shown in Fig. 4A, the fractal dimension of the soil aggregates increased significantly in comparison with the undisturbed soil following different rainfall conditions (P < 0.05). After being splashed by rainfall with an intensity of 5.76 or 68.61 mm h-1, the fractal dimension of the soil aggregates had no significant change (P > 0.05). After being splashed by rainfall at an intensity of 217.26 mm h-1, the fractal dimension was significantly higher than that of the other treatments (P < 0.05). After being splashed by three rainfall intensities, the fractal dimension of the aggregates increased by 2.26%, 2.26% and 3.67% respectively, compared to that of the undisturbed soil.
After raindrop splash, the total specific surface area of the soil aggregates increased significantly (P < 0.05, Fig. 4B). The total specific surface area of the splashed soil was significantly different from that of the unsplashed soil (P < 0.05), but there was no difference between the rainfall intensities of 5.76 and 68.61 mm h-1 (P > 0.05, Fig. 4B). The total specific surface areas of the soil aggregates splashed by rainfall intensities of 5.76, 68.61 and 217.26 mm h-1 increased by 18.82%, 17.79% and 30.24% respectively (Figure 4B).
The specific surface area of the soil aggregate increased with decreasing aggregate particle size, especially for the < 25 μm aggregates (Figure 4C). For the 500-1000 μm aggregates, the specific surface area of soil splashed with raindrops was significantly higher than that of the unsplashed soil (P < 0.05), but there was no significant difference between the different rainfall intensities (P > 0.05, Fig. 4C). After raindrop splash, the specific surface areas of the 250-500 μm aggregates were higher than those of the undisturbed soil, whereas the specific surface areas of the 106-250 μm and 53-106 μm aggregates fluctuated. After being splashed by rainfall at an intensity of 68.61 and 217.26 mm h-1, the specific surface area of the 25-53 μm aggregates was significantly different from that of the undisturbed soil, increasing by 31.99% and 102.50% (P < 0.05), respectively, and the SSA was significantly higher than that of other rainfall intensities (P < 0.05). The specific surface areas of aggregates in the undisturbed soil and splashed soil had a maximum value in the <25 μm range; the specific surface areas of soil splashed by small, medium and large rainfall intensities increased by 9.15%, 10.92% and 17.49%, respectively, compared with undisturbed soil.