Aggregate structure destruction and pore plugging caused by raindrop splashes

Raindrop splash engenders the dispersion and transport of the soil particles,  that is the primary stage in the process of soil erosion. Raindrops with different diameters may have different influences on different soil structures. The research objective was to quantitatively and visually analyze the change in surface aggregates and pore microstructure of five soils (Eum-Orthic Anthrosol, Ustalf, Cumulic Haplustoll, Ustochnept and Quartisamment) in the Loess Plateau caused by various raindrop diameters (2.67, 3.39 and 4.05 mm) using rainfall tests, synchrotron-based X-ray micro-computed tomography (SR-μCT) and digital picture processing. Surface aggregate fragmentation and pore plugging rose as growing raindrop diameter. Under raindrop splash, the increase in raindrop diameter increased the number of microaggregates (≤ 250 μm) of Cumulic Haplustoll, Ustalf and Eum-Orthic Anthrosol; the irregular pore-shape factor of Quartisamment and Ustochnept; and the total number of aggregates and pores. Moreover, the soil physicochemical properties also had a significant impact on surface aggregate breakdown and pore plugging (P < 0.01). Higher sand contents made the soil structure of Quartisamment and Ustochnept more susceptible to splashing. The FD of Eum-Orthic Anthrosol, Ustalf and Cumulic Haplustoll were lower than those of Quartisamment and Ustochnept. The results showed that during rainfall, both raindrop diameter and soil properties affect surface aggregate stability and pore connectivity, which creates the material basis for forming surface crust, clogging pores and reducing the infiltration rate.