Agriculture Reference
In-Depth Information
In a computer analysis of the economic value of earthworm protein based on its amino acid,
fatty acid, mineral, and vitamin contents, it can be seen that it is extremely valuable as feed for
certain animals, particularly eels and young turkeys, and it has the same value for fish, pig, and
poultry feed as fish meal or meat.
METHODS OF PROCESSING ORGANIC WASTES
WITH EARTHWORMS
Processing systems of earthworms range from very simple methods involving low technology such
as windrows, waste heaps, or containers, through moderately complex to completely automated
continuous flow reactors (Jensen 1993; Edwards 1995a,b). The basic principle of all successful
processing systems is to add the wastes at frequent intervals in small, thin layers to the surface of
the system and allow the earthworms to move into this and process successive aerobic layers of
wastes. The earthworms will always move up and concentrate themselves in the upper 15 cm of
waste and continue to move upward as each successive waste layer is added. Many of the operations
involved in vermicomposting can be mechanized; a suitable balance is needed between the costs
of mechanization and the savings in labor that result. The key to combining maximum productivity
of vermicompost with the greatest rates of earthworm growth is to maintain aerobicity and optimal
moisture and temperature conditions in the waste and to avoid wastes with excessive amounts of
ammonia and salts. The addition of organic wastes in thin layers avoids overheating through
thermophilic composting, but enough usually occurs to maintain suitable temperatures for earth-
worm growth during cold winter periods. Hence, for year-round production to maintain a reasonable
temperature in temperate climates, the processing should always be done under cover, although
heating is not usually necessary if the waste additions are managed well with addition of thicker
layers during cold periods to provide some thermophilic composting.
L
OW
-C
OST
F
LOOR
B
EDS
OR
W
INDROWS
Outdoor windrows or beds, either heaped or with low simple walls, are the most common type of
process generally used. The size of such beds is flexible, but the width of the beds should not
exceed 8 ft (2.4 m), which allows the entire bed to be inspected easily. Because there is no need
to walk on the bed, many suitable surface coverings and construction materials can be used. The
length is less important and depends on the area available. They should not be laid on soil because
soil particles would be picked up with the processed vermicompost. Concrete areas are ideal for
earthworm processing systems because they provide a firm surface for tractor operations. However,
it is essential for precautions to be taken to prevent too much water from entering the beds and to
allow excess water to drain away from the bed. Often, the wastes in such floor beds are covered
with permeable material such as canvas or bamboo sheets, which are removed only for watering
and addition of new waste materials. Windrows and floor beds process organic wastes relatively
slowly, often taking 6 to 12 months. During this period, there may be losses of plant nutrients
through volatilization or leaching. The major drawback to windrows is the difficulty in harvesting
the vermicompost and the need for a trommel or other separation stage to recover earthworms from
the vermicompost before it is used. Although the initial capital outlay, other than land, is low, large
areas of land are needed, labor costs are high, and the rate of processing is slow.
C
ONTAINERS
OR
B
OX
S
YSTEMS
Edwards (1988) discussed methods of batch vermicomposting in large or small stacked boxes or
containers and suggested that most of the methods tested were too labor intensive because batches
had to be moved to add more wastes. It is difficult to access them or add water to them because
they are usually stacked one above the other. There have been attempts to develop improved batch
