18.4 Vermicomposting
18.4.1 The Process
The term vermi in vermicomposting is derived from the Latin word ‘vermis’, which
means a worm. However, vermicomposting refers to a composting process that is
done by epigeic, anecic, or endogeic earthworm species, which have a natural ability
to colonize and degrade organic wastes (Bhat et al. 2018; Das et al. 2016). According
to Gomez-Brandon and Dominguez (2014), vermicomposting has thus been defined
as ‘bio-oxidative process in which detrivorous earthworms interact with microorganisms and other fauna within the decomposer community, thus accelerating the
stabilization of organic matter (OM) and greatly modifying its physical and biochemical properties’. Though there are more than 4000 known species of earthworms classified according to the three groups, only a few belonging to the epigeic
class have been shown to be effective for the vermicomposting process mainly due
to their high feed consumption rates, high reproduction rates and high tolerance to a
wide range of environmental conditions (Bhat et al. 2017; Dominguez and Edwards
2011). Among the widely used vermicomposting earthworm species which belong
to the epigeic earthworm class include Eisenia fetida, Eisenia andrei, Eudrilus
eugeniae and Perionyx excavates (Mupambwa et al. 2016; Atiyeh et al. 2000;
Ravindran et al. 2015). Also, though having a low vermicomposting potential,
endogeic species Metaphire posthuma and Drawida barwelli (Das et al. 2016;
Bhat et al. 2017) together with anecic species Lampito mauritii; Apporrectodea
trapezoids and Lumbricus terrestris (Bhat et al. 2017; Anbalagan and Manivannan
2012) have also been used for vermicomposting.
Earthworms have been shown to enhance the composting process directly by
mechanically breaking down larger organic wastes using their gizzards, thus increasing the substrate surface area and consequently altering microbial activity, in
processes that have been collectively called gut-associated processes (Swati and
Hait 2017; Gomez-Brandon and Dominguez 2014). Therefore, apart from the
mechanical action of the earthworms, the microorganisms within the earthworm
gut and the compost are then responsible for producing various bio-compounds like
enzymes and organic acids, which are responsible for accelerating the biodegradation and nutrient mineralization within vermicompost (Dominguez et al. 2010; Aira
et al. 2007), as schematically shown in Fig. 18.2.
According to Dominguez et al. (2010), microorganisms are the most abundant
and diverse members of the vermidegradation food web, with the earthworms being
secondary higher level consumers existing together with microorganisms, which
feed and disperse the microbes. The crucial link between earthworms and microbes
during the vermicomposting process has driven several researchers into trying to
deliberately modify the microbial composition of vermicomposts by inoculating
vermicomposts with specialized microbial cocktails such as effective microorganism
(EM), phosphate solubilizing microbes (PSM), N 2 -fixing bacteria (Mupambwa et al.
2016; Busato et al. 2012; Kumar and Singh 2001). Such microbial cocktails are
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307
18.4.1 The Process
The term vermi in vermicomposting is derived from the Latin word ‘vermis’, which
means a worm. However, vermicomposting refers to a composting process that is
done by epigeic, anecic, or endogeic earthworm species, which have a natural ability
to colonize and degrade organic wastes (Bhat et al. 2018; Das et al. 2016). According
to Gomez-Brandon and Dominguez (2014), vermicomposting has thus been defined
as ‘bio-oxidative process in which detrivorous earthworms interact with microorganisms and other fauna within the decomposer community, thus accelerating the
stabilization of organic matter (OM) and greatly modifying its physical and biochemical properties’. Though there are more than 4000 known species of earthworms classified according to the three groups, only a few belonging to the epigeic
class have been shown to be effective for the vermicomposting process mainly due
to their high feed consumption rates, high reproduction rates and high tolerance to a
wide range of environmental conditions (Bhat et al. 2017; Dominguez and Edwards
2011). Among the widely used vermicomposting earthworm species which belong
to the epigeic earthworm class include Eisenia fetida, Eisenia andrei, Eudrilus
eugeniae and Perionyx excavates (Mupambwa et al. 2016; Atiyeh et al. 2000;
Ravindran et al. 2015). Also, though having a low vermicomposting potential,
endogeic species Metaphire posthuma and Drawida barwelli (Das et al. 2016;
Bhat et al. 2017) together with anecic species Lampito mauritii; Apporrectodea
trapezoids and Lumbricus terrestris (Bhat et al. 2017; Anbalagan and Manivannan
2012) have also been used for vermicomposting.
Earthworms have been shown to enhance the composting process directly by
mechanically breaking down larger organic wastes using their gizzards, thus increasing the substrate surface area and consequently altering microbial activity, in
processes that have been collectively called gut-associated processes (Swati and
Hait 2017; Gomez-Brandon and Dominguez 2014). Therefore, apart from the
mechanical action of the earthworms, the microorganisms within the earthworm
gut and the compost are then responsible for producing various bio-compounds like
enzymes and organic acids, which are responsible for accelerating the biodegradation and nutrient mineralization within vermicompost (Dominguez et al. 2010; Aira
et al. 2007), as schematically shown in Fig. 18.2.
According to Dominguez et al. (2010), microorganisms are the most abundant
and diverse members of the vermidegradation food web, with the earthworms being
secondary higher level consumers existing together with microorganisms, which
feed and disperse the microbes. The crucial link between earthworms and microbes
during the vermicomposting process has driven several researchers into trying to
deliberately modify the microbial composition of vermicomposts by inoculating
vermicomposts with specialized microbial cocktails such as effective microorganism
(EM), phosphate solubilizing microbes (PSM), N 2 -fixing bacteria (Mupambwa et al.
2016; Busato et al. 2012; Kumar and Singh 2001). Such microbial cocktails are
18 Some Perspectives on Vermicompost Utilization in Organic Agriculture
307