Does biochar mitigate rainfall-induced soil erosion? A review and meta-analysis

Biochar has emerged as a promising soil amendment for improving soil structure. Yet, its impact on rainfall-induced soil erosion varies across individual studies. To address this gap, we conducted a statistical meta-analysis of 174 paired comparisons from 45 published studies to integratedly evaluate the impacts of biochar on rainfall-induced soil erosion through biochar and soil properties, as well as experimental conditions. Overall, biochar significantly reduced soil erosion by 27.86%. The response ratio (lnRR) of biochar-induced soil erosion exhibited significant variability across different subgroups. Concerning biochar properties, a more favorable influence was observed in other sources biochar (e.g., manure and sewage sludge biochar) compared to wood based and crop waste biochar, and those produced at lower pyrolysis temperatures (< 500 °C). Increasing biochar dosage was not consistently effective. The optimal range was 0.8%–2%, resulting in a 36.07% reduction in soil erosion. Regarding the soil properties, a higher sand/clay ratio of soil significantly enhanced the performance of biochar (p < 0.0001). Specifically, an insignificant effect was observed in fine-grained soils, whereas the highest reduction of 52.97% was noted in coarse-grained soils. Moreover, long-term field experiments induced greater reductions in soil erosion with biochar (35.30%) compared to short-term laboratory studies (29.62% and 12.59%). This meta-analysis demonstrates that biochar, as a potential soil amendment, could effectively mitigate rainfall-induced soil erosion by considering a combination of soil properties along with specific biochar properties.