Investigating the effect of biochar application on raindrop-driven soil erosion under laboratory rainfall experiments

Rainfall soil erosion is mainly initiated by raindrop splashing. Many studies have addressed the role of biochar in water and soil conservation; however, the processes and mechanisms of soil erosion via raindrop splashing with biochar application remain unclear. Thus, this study investigated raindrop-driven erosion in a silt loam red soil mixed with different ratios of biochar (i.e., 0, 3 %, and 5 %) and groups with different biochar particle sizes (i.e., <0.5, 0.5–1, and 1–2 mm) under artificial rainfall experiments with a high rainfall intensity (68.5 mm/h). A Hydrus 1D combined Rose soil erosion model was employed to explain the hydro-erosion processes. Our experimental results showed that the maximum suspended sediment concentration (SSC) eroded in the surface runoff increased from 12.77 to 14.15 and 15.41 g/L as the amount of biochar application increased from 0 to 3 % and 5 %, respectively. Owing to the decreased infiltration capability, increased surface runoff volume and SSC resulted in the largest amount of suspended sediment (SS) in the 5 % biochar group. Moreover, the biochar grain size also affected raindrop-driven erosion. The mid-sized biochar (0.5–1 mm) had the highest effect on the SSC and the total amount of SS; however, the finer biochar (<0.5 mm) inhibited SS accumulation. Model simulations indicated that biochar application potentially increased the fraction of erodible particles and soil detachability, thereby enhancing raindrop splash erosion. Given that contaminants could diffuse as solid bound (i.e., soil and biochar) and dissolved forms, the trade-off between decreased leaching and increased surface load, or vice versa, under biochar application requires further research to evaluate the associated environmental transport and fate.