Benefits to Soil Fertility and Plant Growth | Important Agricultural Earthworms | The 3 steps for Describing you Paddock Earthworms | Native or Introduced Earthworms | Common Introduced Paddock Earthworms | "A Potential" introduced Paddock Earthworm | Where to go from here ... | Common Native Earthworms | Paddock, Garden and Compost Worms
"This booklet was produced as part of the earthworm research programs funded by Agriculture Victoria (Rutherglen Research Institute), the Grains Research and Development Corporation and the Rural Industries Research and Development Corporation. It acknowledges the input of many of the staff at Rutherglen Research Institute, and particularly the editorial comment of J. Hirth.
All enquiries should be directed to Rutherglen Research Institute, Victoria, telephone (060 304 500.
Wy Do we Need to Know the Types of Earthworms We have in Our Agricultural Soils?
Because 'WORMS AIN'T WORMS"
...... some do better than others to improve soil fertility
This booklet is designed to help you easily recognise the earthworms that you are most likely to encounter in your paddocks and gardens. It will also help you estimate the numbers of earthworms living in your paddock and provide a picture of the general "health" of your soil and the potential to improve it
The life cycle of most earthworms that live in our agricultural soils is dictated by the seasons. All paddock earthworms are active in the surface layer f soil in the wetter, cooler months of May to September.
They feed on soil which contains plant fragments and micro-organisms such as bacteria and fungi. As they feed, they excrete, as casts, the soil they have eaten. These are deposited either at the soil surface or in their burrows.
|Earthworms contain both male and female sexual structures but they usually mate with another earthworm to exchange sperm, rather than fertilise themselves. This occurs during autumn and winter and results in the production eggs, or cocoons.|
The size of these cocoons varies between the different types of earthworms although they are generally between 2 and 4 mm in length. The quantity of cocoons produced in a season depends on the type of earthworm and where they are active.
For example, paddock earthworms that are generally active below the soil surface produce fewer cocoons (about eight per individual) because the risk of mortality. is lower than for other types, such as compost or dung feeders, that live at, or just below the soil surface, where they are more prone to predation. These types produce about twenty cocoons per individual.
Cocoon production can also be related to soil moisture and temperature and the quality and abundance of the soil food supply.
Earthworm Cocoons (x2)
|As the soil starts to dry out in late spring, earthworms burrow deeper into the soil and excavate a small chamber. They seal the chamber and keep themselves moist by rolling up into a ball, and slowly leaking their gut contents. By doing this they can survive the hot, dry conditions of summer. Not all earthworms, however, survive in this way, and rely instead on cocoons to provide the next generation in the following winter. |
Benefits to Soil Fertility and Plant Growth
Earthworms improve soil fertility by their burrowing, casting and feeding. Water and plant roots penetrate deeper into soil in which earthworms have burrowed. Compared to the bulk soil, casts contain greater levels of available plant nutrients, such as phosphorus and nitrogen, as well as more bacteria and fungi. The quantity of nutrients contained in casts depends on the quality of the food the earthworm eats and the age of the casts. Fresh casts tend to have a higher nutrient content compared to old casts. Earthworms also create burrows through which rainfall can drain freely away from the soil surface. Increases in water infiltration of up to 40% means a greatly reduced risk of surface soil erosion and ensures that the plant roots can access this' water more effectively. Earthworm bUlTows also enable plant roots easier passage into compact soils or soils with a hard-pan and provide aeration for these roots. Increased growth of both pasture and crops has been demonstrated where earthworms have been introduced into soils either lacking them, or containing only low numbers. Scientific research has demonstrated pasture production increases of 25%, 20% and 10% in New Zealand, the Netherlands and Ireland, respectively. CSIRO research in' Adelaide has also demonstrated wheat grain production increases of 35% in glasshouse trials, and between 13% and 75% in paddock trials. Individual farmers like Bert Farquhar, who owns 30,000 ha of pastoral land in north-. eastern Tasmania, claims that by introducing earthworms into his paddocks he has increased the fertility of his soil by 25%. The impact that added earthworms have on soil fertility and plant growth will be intluenced by:
The choice of earthworm to add will depend on what is already there. It makes more sense to add a different type of earthworm that is not already there. If earthworm numbers and types are low, then there may be survival problems. If the soil condition is poor because it contains low levels of food and/or is prone to waterlogging, then the success of adding earthworms to improve plant growth, will be low. If, on the other hand, the soil condition is poor because of the presence of a pasture mat, earthworms can work through this and "unlock" a huge nutrient reserve. Plants can then use these nutrients for much improved growth.
Earthworm Hatchling with Cocoons (x1)
A common sight, the surface casts of paddock earthworms
Earthworm burrows at 20 cm depth with plant roots growing through them
|Likes||Earthworms like moist, but not waterlogged soil. They also like plenty of good quality food. Soils containing large quantities of decaying plant material favours large and active earthworm populations. For example, in cropping soils of north-eastern Victoria that contain mulched stubble, the population of earthworms can be 15 times greater than in soils where stubble has been burnt. Perennial pastures containing a good clover mix as well as annual crops sown in rotation with a legume phase, are also favourable farming strategies for maintaining earthworm populations. Earthworms, like aboveground stock, prefer nitrogen rich plant material as a food source. Soils with loam to clay textures are preferred to sandy soils.|
Earthworms dislike dry soil as they need to keep their skin moist to breathe, nor do they like waterlogged soil because they drown. After heavy rain, earthworms can be seen on the soil surface because their burrows have flooded with water. They shun sunlight as they dry out and are prone to sunburn. Those earthworms that like to crawl on the soil surface do so at night. Soils that are excessively cultivated do not support large populations of earthworms. For example, in many cropping soils in southern Australia, populations can be between four and 30 times larger where soil is direct drilled rather than cultivated. Physical damage to the earthworms are the main reasons for such low numbers. Also cultivated soils tend to be drier, particularly early in the season, and contain less food. Earthworms dislike coarse, sandy soils and soils that are compacted.
|Based on short-term (less than five year) studies, inorganic or mined fertilisers and herbicides, when used at recommended rates, do not reduce earthworm numbers although the effect of these chemicals may vary depending on the type of earthworm present. With fertilisers such as superphosphate, earthworm numbers may increase due to increases in pasture production and hence food supply. |
Pesticides that are used to control insects, fungal and bacterial diseases of both crops and animals can be very toxic to earthworms, though few of these have been tested on paddock earthworms. Obviously those pesticides used to control worms (vermicides), including those used as stock drenches, are highly toxic, as are most fungicides. Earthworms will avoid areas that have been heavily dosed with these chemicals.
Some earthworm types are more sensitive than others to soil acidity. Again, if plant production is reduced due to acid soils, the earthworms food supply may be limited.
Predators and parasites of earthworms are not commonly observed except in some irrigated soils where the larvae of a parasitic fly can cause visible twisting and constrictions of the earthworm body. A potentially serious predator native to New Zealand, a planarian flatworm, though not yet found in Australia, has caused widespread devastation to earthworm populations in Ireland. Its requirement for temperatures lower than 20°C may limit its spread in Australia.
|A. caliginosa||grey worm|
|A. trapezoides||purple worm|
|A. rosea||rosy-tip worm|
|L. rubellus||red worm|
|M. phosphoreus||phosphorescent worm|
|M. dubius||organge-saddle worm|
Figure 1. Density of native and introduced earthworms in a paddock survey of
north-eastern Victoria and southern NSW
| The 3 Steps for Describing your Paddock Earthworms |
Step 1. Collection
In winter, when soil is wet, go out into the paddock well away from fence lines and stock camps. If you are familiar with the soil types on your farm, try and sample within common soil types.
Cut a block of soil of surface area of about one square metre and to a depth of 10cm. This is about two by two spade widths (or 30 x 30 cm) to just over one-third spade length (or l0cm).
Lift the block out and turn it over onto the ground or onto a plastic sheet.
|Gently break the block apart and sort through the soil collecting all the earthworms into a container as you go. Most earthworms will be found close to plant roots. Ensure that all earthworms are collected, including the very small or juvenile ones. You may also find cocoons which you can collect as well. After this is done, walk approximately ten paces and cut a second block. Repeat this process in a straight line until a total of five blocks have been sorted through. Note the soil type, pasture composition and the location of the five sites. |
Step 2. Counting
Count all earthworms in your container (which hopefully will be full!!!) and multiply this number by two to obtain the number per square metre. (NB: If you had only sorted through one block of soil then you would multiply by ten).
Although scientists are still trying to decide what is the ideal number, a comparison with the local averages given below will indicate if there is room for improvement in your paddocks.
Pasture paddocks: 160/m2
Crop paddocks: 501/m2
Refer to Table 1 for average densities of common earthworm types.
Step 3. Identification For identification, always select a mature or adult earthworm. The presence of a saddle or "clitellum" indicates that you have a mature specimen.
Look at the following features:
On closer examination:
Figure 2. Arrangement of the setae of earthworms
(A) closely paired, most common; (B) widely paired; (C) distant and (D) numerous, surrounding body (natives)
| Native or Introduced Earthworms? |
This question can only be answered by referring to the three features described in the "on closer examination" section.
Underside of Native (above) and Introduced (below)
| Common Introduced Paddock Earthworms |
The purple worm (Aporrectodea trapezoides)
The purple worm (x1)
|The grey worm (Aporrectodea caliginosa)|
The grey worm (x 1.5)
|The rosy-tip or mucous worm (Aporrectodea rosea)|
A rosy-tip worm (x 1.5 and 3)
|The orange-saddle worm (Microscolex dubius)|
The orange-saddle worm (x1)
|The phosphorescent worm (Microscolex phosphoreus)|
The phosphorescent worm (x1)
|The red worm (Lumbricus rubellus)|
The red worm (x1)
|The yellow-tail worm (Octalasion cyaneum)|
The yellow-tail worm (x1)
| "A Potential" introduced Paddock Earthworm |
The long worm (Aporrectodea longa)
A paddock earthworm that we don't have on mainland Australia but wish that we did!
Top: long worm; Bottom: Purple worm (x0.75)
| Common Native Earthworms|
Native species are much more difficult to identify than the introduced species and many hundreds of species are currently undescribed. The most common native earthworms to be found in paddocks in north-eastern Victoria and southern NSW are referred to as Spenceriella spenceriella. Within this broad grouping there are a number of different forms. Around Adelaide, another type of native earthworm, Gemascolex is more common.
Paddock natives, Spenceriella (x 0.5)
Native earthworms are dark in colour but vary widely in size and many hundreds are thought to remain undescribed. The "scrub worm", and "the giant Gippsland earthworm" are well-known examples of large natives. It is not known if these types improve soil fertility but their occurrence in high numbers in some paddocks (refer back to Figure 1, page 7), both under pasture and crops indicates they may have a role to play.
A common native - the "scrub worm" (x0.5)
|Paddock, Garden and Compost Worms|
|Just as particular plant species prefer to grow in particular environments, earthworms too have specific requirements for growth and breeding. |
If an earthworm is not in its preferred location, and without its preferred food, it is unlikely to survive.
An example of the different needs of different earthworms can be illustrated by looking at paddock and compost earthworms. As we now know, paddock earthworms feed on soil whilst compost earthworms feed on the pure organic matter found in compost heaps.
It is this basic difference that makes compost earthworms unsuitable for introduction into paddock soils.
Because the paddock earthworms work a lot harder to extract nourishment from their food source, they reproduce at a much slower rate. In contrast, compost worms, of which the tiger worm (Eisenia foetida) is the best example, live on a much richer food source and hence reproduce much more rapidly. It is this feature that makes the tiger worm the most commercial species. common commercial species.
In our gardens, we find both soilfeeders (paddock earthworms), and organic matter feeders (compost earth worms). The balance between the two types depends on how much organic matter, as mulch, animal manure, or compost, you have put into your garden.
Compost or tiger worm (x2)
Acknowledgement for the use of this diagram: Dr Geoff Baker, Gaby Kilpin and
CSIRO's Double Helix Science Club