Soil Horizon erodibility assessment in an area of Mexico susceptible to gully erosion

Abstract

Gully erosion is an ubiquitous problem but typically occurs in semi-arid environments. Erodibility (K-index) is the compendium of a set of intrinsic soil properties responsible for resistance to erosion. The number of gully-framed erodibility assessment investigations has been increasing due to the knowledge that it is mainly deep-profile properties that control gully development. Usually, only texture and organic matter are considered when calculating the K-index. In this study, we also consider both the climate factor (through the KUERY algorithm) and chemical stability, through the electrochemical stability index (ESI), an innovation since a direct correlation between K-index and ESI has not been reported. Moreover, erodibility differences between horizons contribute to the dynamics of gully development. Soil horizon erodibility in the studied gullies ranges between 0.036 and 0.006 (Mg·h·m2/MJ·mm·m2), which is within the medium and low erodibility classes but with a growing (more erosive) K-index trend with depth. We found that this is mainly due to electrochemical instability present in the deep horizons (B-Hzs) as suggested by our results and confirmed by the ESI. This allows us to postulate that the higher K-index of the deep layers is promoting the excavation–collapse dynamics, which can explain the large U-shaped gullies present in the area.