Worm farming with piggery solid waste
Figure 1. Site plan for constructing worm beds.
Worm composting or vermiculture uses worms and micro-organisms to convert organic waste into nutrient-rich humus. This process occurs naturally in areas of decaying vegetation such as fallen leaves, manure piles or under rotten logs. The worms feed on both the decomposing organic matter and the micro-organisms - bacteria, fungi and protozoa - that are also actively engaged in the decomposition process.
The organic matter passes through the worm's digestive tract and is excreted as castings. The resulting compost is made up of these castings and other organic wastes. The by-products of this process are water vapour and carbon dioxide, occurring at the natural rate of organic decomposition.
Unlike conventional composting, organic material that is being degraded by worm composting does not reach raised temperatures. Higher temperatures are needed to kill pathogens and weed seeds.
Their are many different types of worms that each have their own role to play in decomposing organic waste, dispersing nutrients throughout the soil and helping to improve soil structure. The last function is a particularly important one.
The types of worms generally associated with the processing of organic waste are Eisenia foetida (commonly known as redworm, brandling worm or tiger worm) and Lumbricus rubellus.
These types differ from the common or garden worm (Lumbricus terrestis) as they naturally occur in the organically rich surface layer of the soil on which they feed. By contrast, the common earthworm is a burrower, requiring large amounts of soil to survive.
Worms are generally raised in beds. These can be small rectangular plots, long windrows on the ground or raised beds. The size of the operation being run will largely determine which system is adopted. When starting a worm farm begin with just a couple of small beds to refine your husbandry and management practices before moving into larger-scale worm farming.
Sheds provide the best sites for worm beds. If not constructed in a shed they can be shaded from the sun and protected from the wind and rain with shade cloth. An insulated shed will protect the beds from temperature extremes. Worm farming has been successful in 'open-air' beds, which greatly reduces the capital input required.
Figure 2. A small worm bed.
A bed size of 1 m wide, 2 m long and 30 cm deep is recommended (Figure 1). Bed width is based on the ease of reaching over to perform management tasks. If bobcats are used, bed widths are generally the width of the bucket. Aisles between beds should be 1 m wide to allow for equipment access and bed management.
Automatic misting sprinklers help to maintain ideal conditions for worm beds. Bed construction materials include brick, cement, hardwood (not oiled), treated pine and clay banks. Drainage from the beds is essential and holes need to be placed at the base of the brickwork or between timber planks.
Beds are generally placed onto the ground (Figure 2) in rows as shown in Figure 1. A cement or other impervious base is ideal, but more expensive. An anti-crawl perimeter is recommended to avoid the mass migration of worms out of beds.
Figure 3. Large-scale worm beds in a commercial environment - on the ground and raised.
Large-scale beds (Figure 3) are more applicable to commercial production. They can be as simple as extended small beds of any length; windrows or more sophisticated raised beds. The advantage of raised beds is that they allow for easier separation of the castings by allowing the dry vermicasts to fall out the bottom when they have been fully utilised by the worms.
A buffer between the vermicomposting operation, nearby water resources (surface and ground water) and neighbouring houses can help to minimise the impact of any odour associated with raw materials (such as manure) and protect the water resources from possible contamination. The buffer will depend on DAF and your local council's recommendations. (For more information on separation distances see Separation guidelines for Queensland piggeries or phone 07 4688 1605).
Any drainage or leachate from the beds should collected or contained. The leachate can be used as liquid fertiliser.
Fill the worm beds with appropriate bedding before introducing the worms. Wet newspaper or cardboard (torn into strips or shredded), soil and mature compost make good bedding material. Other suitable bedding materials include dead leaves, straw, sawdust and peat moss. It is important to establish the right conditions in the beds before the worms are introduced. It may take a few days to achieve the optimal operating temperature and moisture conditions.
Stock a 1 m x 2 m x 30 cm bed with about 1000 (approximately 0.5 kg) mature breeders. Handle them gently and spread them across the surface. Cover the worms with organic matter from the sides of the bed and keep the beds themselves loose so worms can move around freely. The beds should be covered with hessian bags or carpet underlay to help keep light out and to help maintain the correct operating temperature and moisture content.
Worms must be checked regularly. An experienced worm farmer can look after two million worms on a part-time basis. With automatic watering and lighting systems, menial chores are reduced to feeding, periodic harvesting and bed maintenance. Worms will migrate from poorly managed worm beds.
Worms are capable of consuming more than their own weight in organic matter each day from the moment they hatch.
Worms do not have teeth; the organic matter is softened by moisture or by bacterial action in order for it to be sucked into the worms gut where it is further refined in an internal grinding process.
Feeding activity increases at night. Worms anchor their posterior at the mouth of their tunnels for feeding and stretch to their limits to draw food to the hole. The less burrows are disturbed, the more time worms have for feeding, excreting and growing.
The worms can be fed pig manure supplemented with products such as mulched straw or old compost, old sawdust, dried grass clippings, chopped cardboard, shredded paper and old straw. Apply the material to the surface of the beds.
Worms require plenty of food and moisture, a temperature range from 17°C to 25°C is optimum, with minimal disturbance. They are generally less active during colder periods.
Temperature can be increased by adding more organic matter to the bed. If the temperature rises too high, reduce the amount of organic matter added and turn the top of the bed with a fork to increase aeration.
The beds should be watered regularly to maintain moist conditions. The bedding should be kept moist but not wet. If the bedding becomes soggy, dry newspaper or cardboard can be used to bring the moisture back to the optimal level.
Worms require pH conditions between 6.8 and 7.2 for best food digestion. Tiger worms will tolerate higher acidity. The addition of agricultural lime (calcium carbonate) to increase the pH may be necessary. Do not use hydrated lime as it will kill the worms. Adding peat moss or newspaper will increase acidity.
Each earthworm carries both male and female reproductive organs. Two earthworms lie next to each other and are temporarily fused together by a mucoid substance that is secreted by glands of the individual worms. Each worm then deposits a quantity of sperm cells into the other.
The body of the earthworm has a part called the clitellum, usually situated along a third of the length of the worm away from the head. Once copulation is completed, this collar (clitellum) slides off the body of the worm. The fertilised eggs are deposited inside this collar and as the collar becomes detached from the body of the worm the two ends are sealed so it becomes a capsule.
Three weeks after the formation of the capsule, the worms eat their way out and start feeding. On emerging they are about 2 mm long and white in colour but after a few days they assume the typical reddish colour.
Under favourable conditions, worms breed rapidly. They reach maturity in six weeks and can reproduce up to three times a week for up to a year, which is the average life span (although some have been known to live for over four years). In optimum conditions eight worms can produce 1500 offspring within six months. When a worm bed reaches the maximum population it can support, the worms stop breeding and the clitellum thins out and almost disappears.
Large-scale worm farming is a relatively new industry and techniques and machinery are still being developed to mechanise the harvesting process.
Light is a powerful management tool in worm farming. It can be used for harvesting and to avoid the night evacuation of worm beds. After an initial start-up period of three months, worms can be regularly harvested at monthly intervals by carefully removing the bedding to a depth of 10 cm. Fork the worms onto a harvesting tray or table. Harvest in the light by continually scraping manure away from the worms. Worms will crawl to the base of the mound to escape light.
Remove any surface food from the bedding and gently rake off the table back to the bed until worms remain in the last 2 to 5 cm of bedding. Mound this in the centre of the table and take off remaining layers of bedding until mainly worms are left.
Harvesting of open beds can be achieved by applying a fresh food source to the top of the bed, covering it to keep out the light and after one week remove the top layer (containing the majority of the worms). Worms will still remain in the bottom material, but for a commercial operation this system can work effectively.
Beds are usually ready for harvesting when most of the bedding has been depleted, leaving only the castings. There are a number of ways that the vermicasts can be harvested.
Raised beds are generally designed to allow the vermicasts to be collected from the base of the bed, either by falling through, or by mechanical harvesting.
For on-ground beds, the vermicasts can be harvested by first harvesting the worms. Alternatively, the bedding material can be moved to one side of the bed, and fresh bedding and food placed in the empty side. Gradually, the worms will migrate to the new bedding, allowing the old bedding (the pure castings) to be collected. Allowing the migration to occur over a period of about a month will ensure that all capsules remaining in the old bedding have hatched, and the worms migrated.
Background research into marketing opportunities should be conducted before commencing a commercial operation.
Worms are marketed by weight and they weigh between 250 g and 500 g per thousand. In Australia the market price for worms is highly variable.
Worm casts can be marketed as a soil amendment or used on-farm. The addition of castings to soil improves soil structure and water holding capacity. The casts are also rich in nitrate, phosphorus, potassium, calcium and magnesium and offer a good natural substitute for chemical fertilisers. The chemical composition of the castings will depend on the ingredients used in the composting process, but a typical chemical composition of worm castings is shown in Table 1.
By vermicomposting organic waste, more of the nutrients are converted to forms that are more readily available to plants. The nutrients are also released slowly, reducing the risk of nutrient loss by run-off, volatilisation and leaching.
- Murphy, D 1993, Earthworms in Australia, Hyland Publishing Pty Ltd., South Melbourne, Victoria, Australia.
- CSIRO 1991, Earthworms for Gardeners and Fishermen CSIRO Australia, Division of Soils.
- Widust, A 1994, Worms Downunder, Allscap, Mandurang, Victoria, Australia.