Shrink–Swell Dynamics and Complete Profile Reversal in a Smectitic Vertisol from Western Romania: Evidence from a Long-Term Experiment (1967–2020)

Vertisols represent some of the most dynamic pedological systems due to the high content of smectitic clays and the intense shrinkage–swelling processes associated with seasonal variations in humidity. The present work analyzes the dynamics of pedoturbations and the rheological behavior of a smectitic Vertosol located in the Cheglevici experimental field (Aranca Plain, western Romania), continuously monitored for a period of over 50 years (1967–2020). In a stationary experiment, inert markers were buried at depths ranging from 25 to 150 cm to track the vertical displacement of the soil mass. Periodically collected samples were analyzed from a granulometric, mineralogical, chemical, and rheological point of view (plasticity limits, activity index, volumetric shrinkage, free swelling, deformation modulus, cohesion, conventional pressure). The results indicate a high smectite content (69–76%) and rheological indices specific to highly active soils (PI > 35%, A > 1.0, VS > 100%, FS > 140%). The progressive redistribution of the markers provides strong evidence of substantial profile-scale soil redistribution associated with long-term pedoturbation processes, supporting the hypothesis of a near-complete profile turnover over multidecadal timescales. A significant increase in apparent density and a tendency for granulometric homogenization across the profile, associated with structural reorganization, are also highlighted. The study provides long-term experimental evidence on the vertical dynamics of the soil mass in Smectitic Vertisols and reveals major implications for agricultural management, infrastructure stability, and water flow modeling in expansive soils.