Earthworms in Tasmanian Agriculture

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Perhaps the first thing to make clear is that this website is about earthworms that are important to agriculture rather than those found in gardens and used for compost heaps.

Earthworms suitable in agriculture are unsuited to the green material, and high nutrient content, of compost heaps.

The Importance of Earthworms

A soil’s fertility is best described under three headings: biological, chemical and physical. Earthworms impact all three aspects.

Biological fertility.

Their impact on the biology of the soil is primarily by the breakdown of organic matter (plant material and livestock faeces) into humus. Furthermore, earthworms have a very close association with the roots of plants exchanging nutrients suitable for both species. Their activity alongside plant roots stimulates soil microbial activity.

In addition, worm casts assist in the maintenance of soil structure by gluing soil particles together forming soil peds (aggregates of soil particles).

Chemical fertility.

By grinding soil particles to smaller sizes, minerals are released into the soil solution thereby making them more available to plants.

Earthworms assist in the incorporation of lime into the soil.

Physical fertility.

The burrowing activity of earthworms creates pores that allow better air and water infiltration into the soil and in addition can reduce soil compaction. The burrows of earthworms provide channels for root growth.

As a result, studies in Tasmania have indicated that the presence of good populations of exotic earthworms can lead to increases in productivity of up to 20%.

Additionally, the anecic species of earthworms (deep diggers) bring up sub-soil material, thus contributing to the creation of more top soil.

Earthworms can be an important tool in the rehabilitation of industrial (including mining) sites.

While most researchers identify earthworms as benefiting the soil some recent work suggests that they may not be entirely beneficial, particularly under dense native forests in the North East of the USA. (ref.: P Groffman, senior scientist, Institute of Ecosystem Studies, Millbrook, New York).