Effect of Miscanthus × giganteus ash on survival, biomass, reproduction and avoidance behaviour of the endogeic earthworm Aporrectodea caliginosa.

To achieve the EU’s targets for reducing energy production from fossil fuels, the use of energy crops, such as Miscanthus × giganteus, is increasing resulting in a corresponding increase in waste ash from incineration. The chemical properties of Miscanthus ash (e.g. phosphorus and potassium content) may allow this waste material (currently landfilled) to be used as a fertiliser, but no information exists on the effect of the ash on the biological properties of soil. The main aim of this study was to determine the potential impact of Miscanthus ash on earthworms by assessing the effect on survival, change in biomass, reproduction and avoidance behaviour of the geophagous, soil dwelling earthworm, Aporrectodea caliginosa. Tests utilised a range of Miscanthus ash doses from 0 to 50 t ha−1 (0, 1, 2.5, 5, 10, 25, 50). Results showed that Miscanthus ash had no significant impact on A. caliginosa survival, biomass and reproduction, but negative trends were observed for biomass from 2.5 t ha−1 and for reproduction from 10 t ha−1. In contrast, a significant avoidance response was observed in the 25 and 50 t ha−1 treatment and according to ISO guideline 17512 there is a negative impact of the Miscanthus ash on soil habitat function at 25 t ha−1 and above as more than 80% of earthworms were in the control soil. It is suggested that this negative effect on soil habitat function could be attributed to a range of factors including the presence of heavy metals in the ash and a change in substrate pH, texture and/or osmotic stress. Further laboratory-based studies conducted over extended time periods with a more refined range of ash doses and associated field-based studies are required to validate the results and determine a more precise assessment of the threshold ash value inducing a loss of soil habitat function.