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Purpose Constructed soils are Technosols resulting from the deliberate combination of various artefacts. Similarly to natural soils, technogenic parent materials are transformed by pedogenic factors contributing to their evolution. This work was conducted to study the first stages of the pedogenesis of constructed soils. Materials and methods Two soils were constructed in lysimetric plots (10 × 10 m) using an engineering process by the combination of paper-mill sludge, thermally treated soil material and green waste compost. Evolution of the soil profiles, composition of soils and leachates were studied for 3 years. Results and discussion A strong evolution of the profiles was observed over the 3 years with rapid changes in the number and characteristics of the horizons. Significant changes in chemical weathering (decarbonatisation) and physical status (aggregation), i.e. processes similar to those occurring in natural soils were observed. Other processes specific to the technogenic materials were recorded, e.g. massive dissolution of gypsum or drainage of constitutive water. Apart from constructed Technosols classification, prediction was made on their future pedogenic evolution. Conclusions Constructed Technosols made of finely divided reactive organic and mineral compounds were observed to evolve quickly. Evidences of original pedogenic processes have been highlighted that could be considered as a general diagnostic characteristic of Technosols. Finally, some considerations about the application of the World Reference Base for Soil Resources to the classification of Technosols are proposed, taking into account some aspects of their pedogenesis that have been highlighted by our work.

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