Investigating the effect of microbial inoculation on raindrop splash erosion: Indoor simulated rainfall and Hairsine-Rose model analysis

The core physical mechanism of rainfall soil erosion is primarily driven by the raindrop splash erosion process. The application of microorganisms to inhibit rain erosion has been confirmed; however, the raindrop splash erosion process and its underlying mechanisms under microbial application conditions remain unclear. Therefore, in this study, different types of microbial inoculants were applied to the surface of silty clay loam black soil under simulated heavy rainfall conditions, with varying concentrations and inoculation methods, to investigate the response characteristics and underlying mechanisms of microbial effects on the splash erosion process. The raindrop splash erosion process was simulated and analyzed using COMSOL Multiphysics in conjunction with the Hairsine-Rose soil erosion model. The experimental results showed that among the different inoculant concentration treatments, the 107 CFU·mL-1 concentration had the highest infiltration rate and the lowest surface runoff, leading to a reduction in SSC (Suspended Sediment Concentration) by an average of 26.33%, 23.45%, and 6.48% for the B7, C7, and BC7 treatments, respectively, compared to the control group. Meanwhile, the type and application method of inoculants significantly influenced the raindrop splash erosion process. Specifically, the individual inoculation treatments exhibited better inhibitory effects on suspended sediment concentration (SSC) and suspended sediment (SS) compared to the combined inoculation treatments. Among, the individual inoculation of Bacillus subtilis showed the most effective inhibition. The model simulation results indicated that microbial inoculation treatments effectively inhibited raindrop splash erosion by reducing the bare soil detachability (a) and the fraction of eroded sediment (β), while increasing the material required to completely shield the soil (Md). However, considering the dynamic changes of microorganisms in the soil and the ongoing debate regarding their applicability to different soil types and environments, further research is needed to achieve the practical application of this technology in soil erosion control.