Earthworms bring compacted and loose soil to a similar mechanical state

We tested the hypothesis that earthworms stabilise loose soil and loosen compacted soil to a similar mechanical state. Casts collected from initially loose soil (980 kg m−3) had 10-fold greater viscosity (31 kPa s) and 5-fold greater yield stress (200 Pa) than a control soil without worms. Lumbricus terrestris; Dendrobaena sp. and Aporrectodea longa were all investigated, with no difference found between species. In compacted soils (1300 kg m−3), A. longa produced casts with similar mechanical properties to loose soil, with viscosity and yield stress decreased by 45% compared to the control without worms. Earthworms were shown to bring initially loose and compacted soil to an intermediate mechanical state that is more favourable for structural stability and root growth.