Agriculture Reference
In-Depth Information
Organic
residues
Stable product
(nontoxic)
Valuable organic
fertilizer
Pathogens
Fulvic and humic acids
Heavy metals
Specific microflora activity
Organic pollutants
Plant growth regulators
Residue quality
Bad
Stabilization (composting)
Good
Organic fertilizer (vermicomposting)
FIGURE 20.5
Vermicomposting and any other biological treatment of organic wastes can be considered as
two-step processes.
NEW PERSPECTIVES IN VERMICOMPOSTING RESEARCH
Although an interest in vermicomposting research and technology has been increasing at a rapid
rate and the body of knowledge now available is quite large, there are still many questions to
be investigated. The topics of some of these questions are discussed here: the method of
operation, the management of the process, the effect of the earthworms, the timing of the
process or the resident time of the wastes to be converted into real biological soil amendments,
the reason why vermicompost promotes plant growth, or the Ñmean lifeÒ or Ñexpiration dateÒ
of these vermicomposts.
O
PERATION
OF
THE
P
ROCESS
: H
OW
V
ERMICOMPOSTING
W
ORKS
The classical approach in all research projects on vermicomposting and in the case study presented
in this chapter consists of adding earthworms into organic residues and obtaining vermicompost
(see
Figure 20.6A
)
. With a reductionist approach such as this, it is difÝcult to know how the
vermicomposting system works and the role of the earthworms in the process. Figure 20.6B
represents a simpliÝed model of the vermicomposting process; in ways similar to nature, earthworms
obtain their energy from the organic matter, and their effects on the waste depend on the quality
and quantity of the resource and on the earthworm species used. The vermicomposting process
consists basically of two different subprocesses. The Ýrst involves the earthworm gut-associated
processes (GAPs), which include all the modiÝcations that the organic matter undergo during transit
through the intestinal tract, including the transformation of nutrients, modiÝcations and increases
in microbial diversity and activity, modiÝcations of microfaunal populations, homogenization, and
the processes of digestion, assimilation, and excretion of the wastes. Once the earthworm GAPs
end, the resultant casts are exposed to cast-associated processes (CAPs); here, the effects of the
earthworms may be only indirect and include aeration of the substrate because of the burrowing
activities. Moreover, earthworm casts are subject to an aging process and to the action of micro-
organisms and microinvertebrates present in the substrate; it is important to note that, during action
of the vermicomposting systems, the casts are mixed with materials that were not eaten by the
earthworms.
