Soil internal forces contribute more than raindrop impact force to rainfall splash erosion

Soil internal forces, including electrostatic, hydration and van der Waals, play critical roles in aggregate stability, erosion, and other processes related to soil and water. However, the extent to which soil internal forces influence splash erosion during rainfall remains unclear. In the present study, we used cationic-saturated soil samples to quantitatively separate the effects of soil internal and raindrop impact forces (external) on splash erosion through simulated rainfall experiments. An electrolyte solution was employed as rainfall material to represent the combined effects of soil internal and external forces on splash erosion. Ethanol was used to simulate the sole effect of soil external force on splash erosion. The soil splash erosion rate increased with increasing rainfall kinetic energy in experiments with electrolyte solution and ethanol and was also greatly influenced by soil internal forces. Moreover, the soil splash erosion rate increased first (from 1 to 10−2 mol L−1) then leveled off (from 10−2 to 10−4 mol L−1) with decreasing electrolyte concentration in the bulk solution. This finding was in agreement with the theoretical analysis of soil internal forces. The contribution rate of soil internal forces on splash erosion was >65% at a low electrolyte concentration (<10−2 mol L−1) and only 3%-25% at an electrolyte concentration of 1 mol L−1. Even though the electrolyte concentration of the soil bulk solution reached 10−1 mol L−1, the contribution rate of soil internal forces to splash erosion was >50%. Hence, soil internal forces exerted higher contribution to rainfall splash erosion than raindrop impact force under most field conditions. This work provides new understanding of the mechanism of soil splash erosion and establishes the possibility of controlling splash erosion by jointly regulating the soil internal and external forces.