Agriculture Reference
In-Depth Information
N is present initially (Hartenstein 1983; Edwards 1988). Although this conclusion was based on
laboratory experiments, a similar earthworm yield can be expected from field systems that are
managed well.
It is likely that ingestion of organic waste by earthworms stops when a critical level of humified
material appears, rich in free-radical and noningestible content, despite the remaining abundance
of oxidizable carbon (Hartenstein 1983; Hartenstein and Neuhauser 1985). This might account for
the relatively low biomass of earthworms in tropical soils despite the high availability of organic
carbon from vegetation and the rapid rates of soil and organic matter turnover. However, this needs
further investigation.
EFFECTS OF DIET ON THE GROWTH AND
REPRODUCTION OF EARTHWORMS
Earthworms obtain their energy from the organic matter on which they feed, and their effects on
the characteristics of this organic matter will depend on the quality of the resource and on the
earthworm species. Earthworms fragment organic wastes with a grinding gizzard, aided by grit and
sand, and this increases the surface area of the organic matter and promotes very high microbial
activity. Moreover, the earthworms use the microorganisms for a nutrient source rather than the
organic matter.
Vermicomposts can be produced from almost any kind of organic waste with suitable prepro-
cessing and controlled processing conditions. However, the growth and reproduction of earthworms
depends very much on the quality of their food resources in terms of their potential to increase
microbial activity. Depending on this quality, earthworms can invest more energy either in growth
or in reproduction. For example, studying the effect of different residual bulking agents (e.g.,
paper, cardboard, grass clippings, pine needles, sawdust, and food wastes) mixed with sewage
sludge (1:1 dry weight) on the growth and reproduction of
E. andrei,
we found that the maximum
earthworm weights achieved, and the highest growth rates, occurred in the mixture with food waste
added (755 E 18 mg and 18.6 E 0.6 mg day
−1
, respectively), whereas the smallest earthworm sizes
and the lowest growth rate occurred in a mixture of sewage sludge with sawdust (572 E 18 mg
and 11 E 0.7 mg day
−1
, respectively). However, the earthworms reproduced much faster in the
paper and cardboard mixtures (2.82 E 0.39 and 3.19 E 0.30 cocoons earthworm
−1
week
−1
, respec-
tively) compared with the reproduction in the control with sewage sludge alone (0.05 E 0.01
cocoons earthworm
−1
week
−1
) (
Figure 20.2
)
(Domnguez et al. 2000).
ECOLOGY OF VERMICOMPOSTING: A CASE STUDY
An experiment in our laboratory at the University of Vigo in Spain studied a vermicomposting
system with different mixtures of pig manure slurries and agro-forestry by-products. This research
project evaluated the characteristics of the vermicomposts produced after different processing
times. The vermicomposting boxes were sampled monthly during a year; numbers and total
weights of earthworms and cocoons were recorded, and several physical and chemical parameters
were measured.
In most of the vermicomposting systems, an initial decrease in earthworm biomass was
observed at the start of the experiment; this was more marked in the mixtures of pig slurry
with pine bark and pine needles. Later, the earthworm populations recovered, and their biomass
increased gradually to final values that were considerably greater than the initial ones. One
possible cause is that, in microcosm experiments, earthworms are unable to find suitable
ecological habitats and may suffer an initial stress in activity and feeding. As a consequence,
the effects of earthworms on the decomposition of the organic matter were much greater during
the final stages of the process when the earthworm populations were more conditioned and
