Raindrop-impact-induced ejection characteristics of surface particles for soils with a textural gradient

The ejection of surface soil particles caused by raindrops is an important stage of water erosion. Generally, surface soil is typically comprised of more complex structural units (e.g. crumb, block, or platy structures) rather than single granular structures (e.g. aggregate), especially on surface soil influenced by the different arrangement mode between soil particles. Thus, soil aggregate samples as a selected test material cannot properly characterise the particle ejection characteristics of surface soil with more complex structural units during rainfall. Considering this issue, undisturbed soil samples with a textural gradient were collected as test materials for this study and a needle-type raindrop simulator was used to simulate rainfall experiments. Our results demonstrate that, the first 6 min of rainfall is the key period for particle ejection. During this phase of the experiment, the clay-sized and fine-silt-sized particles were preferentially ejected, and the enrichment ratio (ER) of those particles decreased progressively from sandy loam to silty clay loam. With increased rainfall duration, the soils with a low clay content (e.g. sandy loam, silty loam and loam) were found to develop surface crusts more easily compared with clay loam and silty clay loam. Although the formation of soil crust reduced the size-selectivity of the splash-detached particles, the percentage of sand-sized particles in splash-detachment particles showed an increasing trend, while the percentage of clay-sized and fine-silt-sized particles showed a decreasing trend. The finding of this study suggests that identifying changes in the soil surface condition, as determined by soil texture, is the key factor affecting the ejection characteristics of surface soil particles during splash erosion.

Automated summary

The ejection of surface soil particles caused by raindrops is a critical stage of water erosion. Soil with complex structural units, influenced by the arrangement of soil particles, cannot be accurately characterized by soil aggregate samples. In this study, undisturbed soil samples with a textural gradient were used to simulate rainfall experiments. The results show that the first 6 minutes of rainfall is the key period for particle ejection, and the clay-sized and fine-silt-sized particles are preferentially ejected. Changes in the soil surface condition, determined by soil texture, significantly affect the ejection characteristics of surface soil particles during splash erosion.