Growth, reproduction and activity of earthworms in degraded and amended tropical open mined soils:: laboratory assays

The potential of four earthworm species to establish viable populations on soils degraded by the cement industry was tested in laboratory assays. We evaluated growth, reproduction, vertical distribution, and activity of endogeics Pontoscolex corethrurus and Octolasion cyaneum, and epigeics Amynthas corticis and A. gracilis, raised on artificial two layer soil profiles. Bottom layer consisted of mineral subsoil (MS) taken from a cement mine, whereas top layer was an organic substrate. A bifactorial experimental design with eight treatments per species was implemented. MS factor had two levels (pH 5.5 and 7.5), whereas organic substrate factor presented four levels of depth (0.0, 2.5, 5.0, and 13.0). The organic substrate layer varied between species: organic soil (OS) was used with P corethrurus and O. cyaneum, OS mixed with composted coffee pulp was given to A. corticis, whereas vermicomposted coffee pulp was provided to A. gracilis. None earthworm species grew in the MS without an organic layer (OL). Growth and reproduction of P. corethrurus and A. corticis were positively affected by the organic treatments. A. gracilis survived in these treatments, but its growth was negligible. O. cyaneum proved to have little resistance to manipulation since high mortality rates were observed. P. corethrurus and A. corticis had the highest rates of cast deposition into the MS, but R corethrurus was active even in the acid (pH 5.5). Based on vertical distribution and cast production patterns, R corethrurus and, to a less extent, A. corticis proved to have the greatest potential for supporting pedogenic processes through bioturbation. Additional work is necessary to show the effect of species interactions over a range of MS properties. (C) 2002 Elsevier Science B.V. All rights reserved.