Agriculture Reference
In-Depth Information
instance, according to Bilgrami (1996), the mite
Hypoaspis calcuttaensis
preys voraciously on
plant-parasitic nematodes, predaceous nematodes, and saprophagous nematodes. Perhaps vermi-
composts increase numbers of omnivorous nematodes or arthropods that prey selectively on plant-
parasitic nematodes. Vermicomposts might also promote the growth of nematode-trapping fungi
and species of fungi that attack and destroy nematode cysts and affect, either directly or indirectly,
populations of plant-parasitic nematodes (Kerry 1988). Alternatively, rhizobacteria can colonize
roots and kill plant-parasitic nematodes by producing enzymes and toxins that are toxic to them
(Siddiqui and Mahmood 1999). As well as such biotic interactions, abiotic factors provided by
vermicomposts might reduce populations of plant-parasitic nematodes. For example, vermicom-
posts may contain compounds that might affect the survival of nematodes. For instance, nematodes
can be killed by the release of toxic substances such as hydrogen sulfide, ammonia, and nitrates
during vermicomposting (Rodriguez-Kabana 1986).
EARTHWORMS AS A SOURCE OF PROTEIN FOR ANIMAL FEED
Many mammals, birds, and fish prey on earthworms in nature. It was first suggested that earthworms
contain sufficient protein to be considered as animal food by Lawrence and Millar (1945), and this
potential of earthworms as animal feed has been confirmed by full analyses of the body tissues of
earthworms, which show the kinds of amino acids that they contain and the nature of the other
chemical body constituents. The first successful animal feeding trials on earthworms were by Sabine
(1978), but subsequently there have been a number of other such trials by various workers (Edwards
and Niederer 1988).
N
UTRIENT
V
ALUE
OF
E
ARTHWORMS
AS
A
NIMAL
F
EED
The first analyses of the constituents of the tissues of different species of earthworms were by
Lawrence and Millar (1945) and McInroy (1971), and there have been various other analyses since
(Schulz and Graff 1977; Sabine 1978; Yoshida and Hoshii 1978; Mekada et al. 1979; Taboga 1980;
Graff 1982; Edwards 1985; Edwards and Niederer 1988). Some of these show clearly that the
essential amino acid spectrum for earthworm tissues, as reported by these different authors, com-
pares well with those from other currently used sources of animal feed protein, and that the mean
amounts of essential amino acids recorded are very adequate for a good animal feed. In addition,
earthworm tissues contain a preponderance of long-chain fatty acids, many of which cannot be
synthesized by nonruminant animals and an adequate mineral content. They have an excellent range
of vitamins and are rich in niacin, which is a valuable component of animal feeds, and are an
unusual source of vitamin B
12
. The overall nutrient spectrum of worm tissues shows an excellent
potential as a protein supplement to feed for fish, poultry, pigs, or domestic animals.
P
RODUCTION
OF
E
ARTHWORMS
FOR
A
NIMAL
F
EED
IN
A
NIMAL
, V
EGETABLE
,
AND
I
NDUSTRIAL
W
ASTES
The growth patterns of individual earthworms or whole earthworm populations in organic wastes
follow classical sigmoid growth curves, with a rapid initial growth phase followed by a steadier
phase and subsequent leveling. The maximum protein production per unit time can be achieved
by inoculating relatively large volumes of animal wastes with small numbers of young worms
to take maximum advantage of the initial fast phase of population growth. Dry matter conversion
ratios of waste to earthworm biomass, which range from 10% for cattle and pig waste (
Figure
18.1
) to 2% for duck waste, have been achieved readily in the laboratory, although rather lower
conversion rates have been attained in the field because of the difficulty of maintaining optimal
conditions.
