In the early 1950s, at the Ruakura Animal Research Station in Hamilton, pasture growth was measured on several soil types with and without lumbricid earthworms. The study showed increases of 30–110% in grass growth in response to earthworm activity.
Similarly, in the Otago upland soils, introduced Aporrectodea caliginosa earthworms improved pasture production by 29% after 16 years.
While earthworms are generally seen as beneficial, people playing golf or rugby may not appreciate their casts – mounds of nutrient-rich soil. Worms in sports turf are sometimes killed, the soil is scarified, and plant debris is removed to improve drainage and discourage worms.
As earthworms feed on organic material it is not surprising that they thrive in compost heaps – especially introduced species such as Eisenia fetida and E. andrei. Compost worms, like those in litter and dung, are very efficient at breaking down organic matter. But they are not burrowers, and do not directly contribute to improving soil structure.
The typically damp, organic-rich conditions in compost heaps contrast strongly with those in soil, and different earthworms occupy the two habitats. But as compost normally sits on soil, both types of earthworm may occupy this zone. The larger, soil-dwelling worms are not efficient at breaking down compost, so they should not be put into compost heaps.