Technosols made with various urban wastes showed contrasted performance for tree development during a 3-year experiment

Vegetation in urban areas is generally living in a stress-inducing environment. Sustaining good soil quality is crucial to improve tree development and heath in such (artificial) environment. This study investigates the dynamics of the physico-chemical properties of Technosol, and compares tree development performances in various waste mixtures. A 3-year experiment was conducted with Acer platanoïdes L. grown in three distinct constructed soils, in three replicates, in 0.480-m³ lysimeters in Angers (France). Four combinations of artefacts were studied either as “growing material” (GM) or “structural material” (SM). Three different SMs were used: (1) a mixture of fine mineral material, demolition rubble and green waste (SM-DR/GW), (2) a mixture of fine mineral material, track ballast and sewage sludge (SM-TB/SS), and (3) the SM currently used by Angers city for green space settlements (SM-CT). Waste characteristics and mixing proportions both affected tree development. Physical properties were not a limiting factor for tree development, despite a relatively low soil water reservoir due to high stone content. Moreover, the chemical properties of the materials, more particularly low water pH and CEC, led to poor tree development in SM-CT, whereas the other two SMs did not affect tree development. SM-TB/SS was the most suitable constructed soil after 3 years because it exhibited satisfactory soil nutrient contents that promoted the best tree crown quality. Waste mixtures can sustain soil functions for tree development. As for urban street tree pits that are 2–8 m³ in volume, soil water, and nutrient autonomy should satisfactorily sustain tree development.