Potential of excavated materials to construct Technosols for ornamental plant covers and green lawns

Constructed Technosols may contribute to urban green infrastructure development while recycling urban waste and preserving natural soil resources. A number of studies have been carried out into the potential of constructed Technosols for tree planting, meadows and urban agriculture. However, the literature is still very limited when it comes to ornamental plants, such as groundcover perennials and grasses. This study assesses the performance of twelve groundcover species and three grass compositions for lawns cultivated in three different constructed Technosols, comparing them to a reference topsoil.

The experiment, conducted at a horticultural institute on the outskirts of Paris, utilized outdoor conditions with the in-situ topsoil serving as a control (CT). Three Technosols were constructed using different excavated soils mixed with composted green waste (10% V/V): T1 (loamy-clay deep soil horizon), T2 (sandy-loam deep soil horizon), and T3 (calcareous-clay regolith). Non-grassy perennials used as ground cover were promptly planted once materials were assembled, followed by the sowing of three different grass compositions for lawn six months later. The foliage coverage of both perennials and grasses was then assessed over the subsequent two years at the beginning of summer season. A total of 12 perennials were introduced, including Armeria maritima, Chamaemelum nobile, Erigeron karvinskianus, Herniaria glabra, Nepeta mussini, Pratia pedunculata, Prunella grandiflora, Satureja montana, Sedum sexangulare, Stachys byzantina, Thymus serpyllum, Vinca minor. The performance of the perennials was also assessed based on qualitative factors such as vigor and aesthetics.

The physicochemical properties of all constructed Technosols differed from the control topsoil and among themselves. However, despite this variability, most plant species in all Technosols demonstrated growth and development comparable to those in the topsoil, including flowering. However, significant differences in foliage coverage were observed across the substrates for seven out of twelve perennial species. Perennials tended to grow better in soils with finer textures, such as the topsoil and one type of constructed Technosol. Conversely, lawn grasses grew better in Technosols with coarser textures.

The trial findings indicate that constructed Technosols can support ornamental plant covers and green lawns, performing similarly to natural topsoil. Our findings emphasize the necessity of adapting usage to the specific properties of constructed Technosols. Additionally, this study aids in selecting cultivars for cultivation in each type of substrate. Lastly, it emphasizes the importance of understanding the temporal dynamics of constructed Technosols' to improve the success of their application in green infrastructure.