Agriculture Reference
In-Depth Information
A
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+
VERMICOMPOST
B
Earthworm
gut
RESOURCE
QU ALIT Y
ORGANIC
MATTER
CASTS (t 0 t x )
GAPs
Nutrients addition
Microbial activity
Homogenization
Digestion
Assimilation
Excretion
CAPs
SPECIES
Aging
Microbial activity
Microfauna activity
Mineralization
Humification
FIGURE 20.6 Different strategies on vermicomposting research: (A) classical approach utilized in most
studies; (B) split approach in two different processes, gut-associated processes (GAPs) and cast-associated
processes (CAPs).
One example of these two different ways to study the vermicomposting process is given in
Figure 20.7 . The number of total coliform bacteria remains more or less stabilized in pig manure
in the absence of earthworms and decreases sharply in the presence of earthworms (Figure 20.7A);
the passage through the earthworm gut (GAP) does not affect human pathogen populations (Figure
20.7B), and the effect of the CAPs on human pathogen numbers after 2 months is quite different
in the noningested waste, in the mixture of casts and waste, and in the casts, with these presenting
the lowest numbers (Figure 20.7C). Studies of the vermicomposting process through such different
compartments can give more detailed information of the biotic and abiotic changes in the organic
wastes.
T IMING OF THE V ERMICOMPOSTING P ROCESS AND L ONGEVITY OF V ERMICOMPOSTS
Directly related to the explanation above is the timing of the vermicomposting process, such as
when the process is completed, and if there is an optimum level of biotic activity in the vermicom-
post. The Ýrst phase, the passage of the organic matter through the earthworm gut (GAP), is rapid,
and it is important to determine the magnitude and importance of the biochemical and physical
changes during this gut transit. Once the fresh earthworm casts are deposited, then something like
a ÑmaturationÒ process of these casts starts. During this aging, vermicomposts reach an optimum
in terms of biological properties that promote plant growth and suppress plant diseases. There are
no data about when this optimum is achieved, how it can be determined, and how to determine if
this optimum has some kind of longevity or expiration date ( Figure 20.8 ).
E FFECTS OF V ERMICOMPOSTS ON P LANT G ROWTH
Earthworms have beneÝcial physical, biological, and chemical effects on soils, and these effects
can increase plant growth and crop yields in both natural and agroecosystems (Edwards and Bohlen
1996; Edwards 1998) (see Chapter 18 this volume). These beneÝcial effects have been attributed
to improvements in soil properties and structure (Kahsnitz 1992), to greater availability of mineral
 
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