Did you know?

• Earthworms are an indicator of soil health.
• There are nearly 200 different species of earthworm in New Zealand.
• There are many species of native earthworms, but these seldom occur in developed soils.
• The most commonly found species originated in Europe and arrived with the early settlers.

Different earthworms, different homes

There are 4 main types of earthworm:

1. Surface dwellers:
   • Feed on dung, decaying roots shoots and leaves
   • Tend to be pigmented / highly coloured.
   • Mix organic matter into soil.
   
   Surface dwellers: Lumbricus rubellus
2. Topsoil dwellers:
   • Most common kind of earthworm in NZ.
   • Live in the top 20- 30 cm depth of soil.
   • Burrow through the soil, eating and excreting it.
   • Continuously create new burrows in soil.
   
   Topsoil dwellers: Aporrectodea calignosa
3. Subsoil dwellers:
   • Live in burrows as deep as 3 metres below the surface.
   • Get food from the surface and drag it to their burrows to eat.
   • Tend to be larger than other types.
   • Mainly confined to the North Island of NZ.
   
   Subsoil dwellers: Aporrectodea longa
4. Compost dwellers:
   • Live in composting areas, but will not usually survive in soil, unless very high in organic matter.
   
   Compost dwellers: Eisenia foetida

How do earthworms help the soil?

Earthworms provide fertile productive soils:

Weight of earthworms below healthy productive pastures
= Weight of animals grazing above ground.

How many earthworms do you need?

The more earthworms the better

There is a distinct difference in earthworm numbers according to the type of cultivation.  Direct drilling maintains higher earthworm numbers than conventional cultivation - in some cases, up to 4 times higher.

Average numbers in the Canterbury region:

• 900 earthworms per metre squared under pasture
• 100 earthworms per metre squared under cultivated crops.

Effect of cropping history on earthworm population numbers

Do I have enough earthworms?

There are a number of signs indicating a lack of earthworms. Does your farm show any of the following?

• A turf mat of decomposing peat-like material on the surface.
• Old dung and plant material lying about on the surface not breaking down.
• Lower-producing grasses more evident than ryegrass.
• Slow pasture growth in spring which stops in early autumn.
• Plant roots that are relatively shallow and prone to drought.
• Water runs off the pasture instead of being absorbed.
• A lack of mixing of fertiliser, lime or organic matter.

How to monitor earthworm numbers:

Select 2 sites representative of the paddock.  At both sites:

1. Cut away any plant matter from the sample areas.
2. Using a standard spade, collect 2 spadefuls of soil to a depth of 20 cm.
3. Spread soil out on a plastic groundsheet.
4. Sort through a handful at a time and count the number of earthworms.
5. Add the number of earthworms from each site and multiply the total by 8.

This will give you a good estimate of the number of earthworms per square metre.

How can I increase earthworm numbers?

Apply agricultural lime fertilisers

• Increase soil calcium levels to near 7, as calcium promotes earthworm reproduction.
• Maintain soil pH between 5.8-6.3.
• Limit use of pesticides (particularly fungicides and fumigants).
• Apply fertiliser, which will increase plant growth and result in higher organic matter being available as an earthworm food source.
• Avoid ammonium based fertilisers, as they make soils acidic.

Irrigation

• Moist soils promote earthworm spread and activity.
• Irrigate during summer months.  More earthworms will remain active in the topsoil in summer under irrigation.
• Avoid over irrigating, as earthworms will have to rise to the surface, and will often die in the heat.

Cultivation techniques

• Use direct drilling /no-tillage rather than conventional cultivation.
• Use mould board or disc plough rather than rotary hoe.

Crop rotation

• Grow pasture, as this increases organic matter which acts as a food source for earthworms. Cropping farms should include a phase of pasture in their cropping rotation to increases organic matter returns.

Use of mulches, manure and crop residues

• Increase organic matter by incorporating composted material, animal manure and crop residues into the soil.

How do I introduce earthworms?

• Lift turves from high earthworm areas and place on deficient pasture.
• Cut turf 200 x 200 x 50 mm and distribute 10 m apart.
• Introduce new earthworm turves after a period of rain, so soil is moist.
• Earthworms will move down into the more moist soil as turves dry.
• Identify source areas when soils are wet and earthworms are casting on the surface; these may be near homesteads, trees, shelter belts, areas that are greener in spring.
• Source areas should have at least 500 earthworms per m for maximum establishment rates (about 20 per spade square).
• Agriculture New Zealand has machines that are purpose-built to cut turves and distribute while applying lime under the turf.

Acknowledgements:

Information on this page was obtained from:

• Dr Trish Fraser and Dr Mike Beare, Crop and Food;
• North Otago Sustainable Land Management Guidelines;
• Dairying and the Environment Committee.