Agriculture Reference
In-Depth Information
A
B
160
140
120
100
80
60
40
20
0
P. excavatus
(1.1-1.4)
L. rubellus
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
D. veneta
D. nepalensis
Eisenia fetida
& E. andrei
E. eugeniae
D. rubida
D. rubida
P. excavatus
Eisenia
D. veneta
E. eugeniae
D. nepalensis
L. rubellus
FIGURE 20.1
(A) Length of the life cycle and (B) mean cocoon production of the earthworm species suitable
for vermicomposting.
suitable zones in the waste, leave the waste, or die, so that the wastes are processed only slowly.
This means that processing under some form of cover is preferable.
T
EMPERATURE
Earthworms have fairly complex responses to changes in temperature. Neuhauser et al. (1988)
studied the potential of several species of earthworms
to grow in sewage sludge, and they concluded
that all these species have a range of preferred temperatures for growth ranging between 15 and
25AC. In their studies, cocoon production was restricted more by temperature than by growth, and
the species studied produced most of the cocoons at 25AC. Edwards (1988) studied the life cycles
and optimal conditions for survival and growth of
E. fetida, D. veneta, E. eugeniae,
and
P. e xcavatus
.
Each of these four species differed considerably in terms of response and tolerance to different
temperatures. The optimum temperature for
E. fetida
was 25AC, and its temperature tolerance was
between 0 and 35AC.
Dendrobaena veneta
had a rather low temperature optimum and rather less
tolerance to extreme temperatures. The optimum temperatures for
E. eugeniae
and
P. e xcavatus
were around 25AC, but they died at temperatures below 9AC and above 30AC. Optimal temperatures
for cocoon production were much lower than those most suitable for growth for all these species.
Temperatures below 10AC generally resulted in reduced or little feeding activity; below 4AC,
cocoon production and development of young earthworms ceased completely (Edwards and Bohlen
1996). In extreme temperature conditions, earthworms tend to hibernate and migrate to deeper
layers of the windrow or soil for protection. It appears that earthworms can acclimate to temperature
in autumn and survive the winter, but they cannot survive for long periods when exposed to freezing
conditions.
The unfavorable effect of high temperatures (above 30AC) on most species of earthworms is
not entirely a direct effect because these warm temperatures also promote chemical and microbial
activities in the substrate, and the increased microbial activity tends to consume the available
oxygen, with negative effects on the survival of earthworms.
M
OISTURE
C
ONTENT
There are strong relationships between the moisture contents in organic wastes and the growth rate
of earthworms. In vermicomposting systems, the optimum range of moisture contents for most
species has been reported to be between 50 and 90% (Edwards 1998).
Eisenia fetida
can survive
in moisture ranges between 50 and 90% (Sims and Gerard 1985; Edwards 1988) but grows more
rapidly between 80 and 90% in animal wastes (Edwards 1988). Reinecke and Venter (1985) reported
