The economic value of earthworms in soil formation was
calculated based on the assumptions that the mean biomass
of an earthworm is 0.2 g (Fraser et al., 1996) and that 1 tonne of
earthworms forms 1000 kg of soil ha−1yr−1 (Pimentel et al.,
1995). The value of purchased top-soil in New Zealand is US
$23.60 tonne−1 (