Although the set-up of our study did not allow us to determine the reason for this variation, the similar chemical properties at the end of the experiment in the soil treated with compost or vermicompost and similar chemical properties of the compost and vermicompost substrates question the long term interest of using vermicompost for the sustainable management of soil fertility.
As expected, this study also confirmed the improved development and activity of earthworms in compost – amended soil (hypothesis 2).
Consequently, an interaction between compost and earthworm activity was reported.
However, contrary to hypothesis 3, the influence of earthworms was not always positive and a negative influence was observed for the second maize cultivation.
Thus, overall, this study highlighted the complexity of the interactions between the quality of OM in soil, earthworm activity and plant growth.