THE EFFECTS OF 3 EARTHWORM SPECIES ON SOIL MACROPOROSITY AND HYDRAULIC CONDUCTIVITY

The burrowing characteristics of three common introduced European lumb ricid earthworm species were studied in New Zealand agricultural soils . Large (30 cm internal diameterx50 cm high) cylinders were filled wit h topsoil (0-25 cm) and subsoil (25-50 cm), sieved to remove earthworm s and other soil macrofauna. Cylinders were inoculated with either mat ure Aporrectodea caliginosa, Octolasion cyaneum (both endogeic species ) or Lumbricus rubellus (an epigeic species) at the rates of 300 and 6 00 m(-2). Additional control (nil earthworms) and mixed species treatm ents were also included in the experiment. Cylinders were buried in th e field for six months before sampling. After six months, most of the introduced O. Cyaneum and L. rubellus earthworms had died, but signifi cant populations of A. caliginosa were present in all treatments. Howe ver, it appears that the different species of inoculated earthworms ha d created contrasting burrowing patterns. L. rubellus was most active in the top 10 cm of the topsoil, although it did create burrows to at least 21 cm depth. L. rubellus did not create any burrows in the subso il. Both A. caliginosa and O. cyaneum burrowed relatively evenly throu ghout the topsoil. Both species also created burrows at all depths sam pled in the subsoil. Under saturated conditions, most water how occurr ed through earthworm burrows. In the topsoil, burrows of A. caliginosa were more continuous and better connected to the soil surface than bu rrows of O. cyaneum. In contrast, O. cyaneum created the most continuo us burrows through the subsoil.