Vermicomposting as a Sustainable Option for Managing Biomass of the Invasive Tree Acacia dealbata Link

The tree Acacia dealbata is native to Australia but has become invasive in many parts of the world thanks to its N-fixing capacity and to the allelopathic compounds present in its biomass. We conducted a pilot-scale study to assess the potential conversion of A. dealbata biomass by vermicomposting via the earthworm Eisenia andrei . The flowering aerial A. dealbata biomass was shredded and placed in a vermireactor under greenhouse conditions for 56 days. The vermicomposted material was sampled every two weeks to analyse its biological and chemical parameters. The phytotoxicity of the fresh A. dealbata material and vermicompost was assessed via an ecotoxicological test with Lepidium sativum seeds. The activity of the earthworms caused strong modifications of the properties of the processed material: the electric conductivity, basal respiration, and organic matter content were reduced, whereas the concentrations of other elements such as N, P, or Zn increased. The earthworm biomass increased steadily until day 42 and then decreased, probably due to the depletion of labile organic matter during the initial stages of vermicomposting. The fresh A. dealbata material reduced the germination and radicle elongation of L. sativum , whereas vermicompost showed the same values as control. The produced vermicompost was an organic fertiliser rich in N and was not phytotoxic. Vermicomposting provides an opportunity to create a new value chain for the control of the invasive tree A. dealbata .