Influence of sewage waste on the abundance of earthworms in pastures in south-eastern Australia

The use of biosolids in pasture-based livestock production is being considered for disposal of human sewage waste in New South Wales (NSW), Australia. An experiment was commenced in 1992 near Goulburn to assess some of the risks associated with the application of dewatered biosolids (DWB) to pastures. DWB was applied to infertile, acidic soils at the rates of 30, 60 and 120 tonnes ha–1 and compared to a fertilised and limed control. In 1999, earthworm abundance was low in control plots (7.5 worms m–2). Application of DWB increased abundance, peaking at 60.0 worms m–2 in the 30 tonnes ha–1 treatment, with no significant difference between the three rates of DWB. The earthworm fauna consisted of exotic Lumbricidae and Acanthodrilidae (most commonly Aporrectodea trapezoides (Duges) and Microscolex dubius (Fletcher)) and native Megascolecidae (most commonly Spenceriella macleayi (Fletcher)). Species composition varied with rate of DWB. Two lumbricids (A. longa (Ude) and A. caliginosa (Sav.)), which were not previously present at the site, were inoculated together in replicated cages in each of the DWB treatments. Three months later, more A. longa were recovered than A. caliginosa (90% cf. 69%), but there was no influence of DWB on the survival of either species. The total biomass of recovered worms also did not vary in relation to DWB. The inoculation of A. longa and A. caliginosa increased pasture production in all the fields (overall increase = 46%). The inoculation of A. longa and A. caliginosa also decreased the abundance and biomass of local earthworms.