Introduction of earthworms into constructed soils has long-lasting effects on primary production

Earthworm inoculation is a successful practice to restore degraded soils. Recently, it has also been used to improve the fertility of Technosols constructed with urban wastes. However, there is still a lack of documentation on long-term effects of earthworms inoculation. In this study, we conducted an outdoor experiment to evaluate the effect of an anecic species (L. terrestris) on primary production, 5 years after their inoculation into Technosols constructed with excavated mineral materials and different doses of green waste compost (10, 20 and 30%). This experiment demonstrated that 1) earthworm inoculation improved perennial plant biomass and 2) this effect was higher on soil containing the lowest amount of organic matter. Soil analyses also revealed that the positive effect on plant biomass could be due to a better availability of phosphorus and potassium. Although the underlying mechanisms still have to be explained, this study showed that the inoculation of ecosystem engineers can improve constructed Technosols fertility in the long term.