3 RESULTS
3.1 Soil aggregatequantitative characteristics
Raindrop splashing increased significantly with rainfall intensity (P < 0.05, Table 2) and resulted in an increase in the number of soil aggregate fragments. Compared to the undisturbed soil, the total number of soil aggregate particles increased by 38.71%, 46.77% and 76.77% after the impacts of rainfall intensities of 5.76, 68.61 and 217.26 mm h-1, respectively (Table 2). Overall, the number of soil aggregate particles in the undisturbed and disturbed soil showed an ”increasing-decreasing-increasing” trend as the aggregate particle size decreased (Fig. 3A). Following raindrop splashing, the number of aggregate particles with different sizes (except for larger aggregates of 500-1000 μm) was higher than that in the undisturbed soil. After raindrop splashing, the quantity of soil aggregate fragments between 250-500 μm increased by 34.88%, 27.91% and 44.19%, respectively, compared to the undisturbed soil (P< 0.05, Figure 3A). After splashing with a rainfall intensity of 217.26 mm h-1, the largest quantity of aggregate particles existed in the 106-250 μm range, accounting for 53.36% of the total amount; this value was significantly increased by 98.65% compared to that of the undisturbed soil (P < 0.05, Figure 3A).
With the increase in rainfall intensity, the total volume of aggregate fragments raised gradually (Table 2). Compared to the undisturbed soil, the difference was not significant after the impact with a rainfall intensity of 5.76 mm h-1 (P > 0.05, Table 2). Following impact with rainfall intensities of 68.61 and 217.26 mm h-1, the total volume of aggregate fragments increased 3.21% and 3.73%, respectively, (P <0.05, Table 2). The percentage of aggregate volume (%) was the ratio of the aggregate volume of a particles size aggregate to the total aggregate volume in a soil clod, which reflected the distribution of aggregate fragments in the soil. The percentage of aggregate volume under different treatments showed a trend of increasing first and then decreasing with the decrease of particle size, and reached the maximum at 500-250 μm. Compared to the disturbed soil, the aggregate in 500-250 μm of the disturbed soil impacted by 5.76, 68.61 and 217.26 mm·h-1 rainfall intensity were significantly (P< 0.05) increased by 39.49%, 25.41% and 24.76%, respectively (Fig. 3B). The percentage of aggregate fragments that were >500 μm in disturbed soil was lower than that of undisturbed soil (P < 0.05), while it was higher for fragments < 500 μm than that of undisturbed (Figure 3B). In addition, for fragments >106 μm, the volume of soil aggregate particles accounts for more than 99.00% of the total aggregate volume (Figure 3B).