Soil genesis and evolution on calanchi (badland-like landform) of central Italy

- Recognizing land facets may help in understanding soil genesis in the calanchi.
- The pedogenesis in the calanchi may progress until a critical threshold.
- Soil water retention also depends on NaCl content.
- Clay dispersion at depth may trigger accelerated erosion phenomena.
- Pedogenesis on calanchi alternates with erosion phenomena rejuvenating the surface.

Calanchi are badland-like erosional landforms, common in the Mediterranean region, which form from accelerated erosion processes. The calanchi slopes, naked or differently vegetated, can be considered as formed by different ecological tesserae originated by the mutual interaction of several factors such as erosion, geomorphology, microclimatic conditions, vegetation, ground cover, and pedogenesis. However, information about pedogenesis is rather scarce mainly because the soils developing on calanchi slopes are incessantly disturbed by erosion processes. To understand the role of soil evolution on landslide erosion, we considered three land facets each one made up of four tesserae (T1 to T4), which represented the different steps of soil and vegetal evolution of calanchi. The soil of each tessera was described, sampled by genetic horizons, and the samples were characterized for their physical, mineralogical and chemical properties. Field observations and laboratory data suggest that pedogenesis in the calanchi badlands may progress until a critical threshold. Indeed, advanced plant colonization and solum development improve soil structure, increase soil organic matter, and favor redistribution of nutrients along the profile. The improvement of structure at depth fosters water storage and clay dispersion through soil leaching and reduction of ionic strength of the soil solution, making soil less stable. Depending on the slope gradient, the soil weight acquired during rainfall events may trigger landsliding, mudflows, or collapses that rejuvenate the surface.