During the vermicomposting process and mainly in the CAPs, low molecular
weight organic acids which include oxalic, formic, citric, acetic acids among others
are produced (Busato et al. 2012). These organic acids have been observed to play a
crucial role in nutrient mineralization during vermicomposting, but have, however,
received limited research attention (Bolan et al. 1994; Kumari et al. 2008). Though
these organic acids are not produced directly by the earthworms, the earthwormmicrobe driven process of organic decomposition during vermicomposting produces
these organic acids which are crucial in nutrient mineralization, particularly in
releasing inorganically bound nutrients (Busato et al. 2012). These organic acids
have been reported to cause this mineralization via three processes which include
competition for adsorption sites, dissolution of adsorbents and changes in the surface
charges of adsorbents (Bolan et al. 1994). So, nutrient release during vermicomposting
can be viewed from both a biological and chemical perspective. Much of the research
has, however, focused on the biological aspects of vermicomposting related to nutrient
mineralization, with limited attention being given to how changes in other chemical
properties such as organic acids influence nutrient mineralization.
18.4.2 Nutrient Enrichment of Vermicomposts
Though vermicomposts are being promoted as organic fertilizers, their adoption as
commercial fertilizers in agriculture is limited by their low macronutrient concentrations relative to inorganic fertilizers. For example, commercial inorganic fertilizers can have as much as 46% N, 48% P, whilst vermicomposts have been reported
to have around 0.96% N and 0.21% P when made from cow dung and banana wastes
(Padmavathiamma et al. 2008). In another study, Singh et al. (2008) reported
macronutrient levels of N (0.92%), P (1.21%) and K (1.45%) for a vermicompost
prepared from vegetable waste and cow dung. This means that, to achieve the same
nutrient level as inorganic fertilizers, organic sources of nutrients need to be applied
at higher volumes per land area or amended with inorganic fertilizers sources as
suggested by Singh et al. (2008) and Arancon et al. (2006). However, organic
fertilizers have other extra benefits such as improving soil physical, chemical and
biological properties, slow release of nutrients, reducing physiological disorders in
vegetables and being environmentally friendly if properly managed, compared to
inorganic fertilizers (Singh et al. 2008; Das et al. 2016). As a solution to the low
nutrient content of organic fertilizers, several researchers have looked at the potential
of amending vermicomposts with other nutrient-rich inorganic materials (Kumar and
Singh 2001). One important macronutrient whose concentration can be enhanced
through amending vermicomposts with inorganic materials is phosphorus (P), and
this has been the subject of several studies (Bhattacharya and Chattopadhyay 2002;
Edwards et al. 2010; Adhami et al. 2014).
Apart from nitrogen, phosphorus is the most important plant nutrient that plays
critical roles in almost all major bio-chemical processes within plants such as
photosynthesis, energy transfer and molecular biosynthesis (Roy 2017; Sharma
18 Some Perspectives on Vermicompost Utilization in Organic Agriculture
309
weight organic acids which include oxalic, formic, citric, acetic acids among others
are produced (Busato et al. 2012). These organic acids have been observed to play a
crucial role in nutrient mineralization during vermicomposting, but have, however,
received limited research attention (Bolan et al. 1994; Kumari et al. 2008). Though
these organic acids are not produced directly by the earthworms, the earthwormmicrobe driven process of organic decomposition during vermicomposting produces
these organic acids which are crucial in nutrient mineralization, particularly in
releasing inorganically bound nutrients (Busato et al. 2012). These organic acids
have been reported to cause this mineralization via three processes which include
competition for adsorption sites, dissolution of adsorbents and changes in the surface
charges of adsorbents (Bolan et al. 1994). So, nutrient release during vermicomposting
can be viewed from both a biological and chemical perspective. Much of the research
has, however, focused on the biological aspects of vermicomposting related to nutrient
mineralization, with limited attention being given to how changes in other chemical
properties such as organic acids influence nutrient mineralization.
18.4.2 Nutrient Enrichment of Vermicomposts
Though vermicomposts are being promoted as organic fertilizers, their adoption as
commercial fertilizers in agriculture is limited by their low macronutrient concentrations relative to inorganic fertilizers. For example, commercial inorganic fertilizers can have as much as 46% N, 48% P, whilst vermicomposts have been reported
to have around 0.96% N and 0.21% P when made from cow dung and banana wastes
(Padmavathiamma et al. 2008). In another study, Singh et al. (2008) reported
macronutrient levels of N (0.92%), P (1.21%) and K (1.45%) for a vermicompost
prepared from vegetable waste and cow dung. This means that, to achieve the same
nutrient level as inorganic fertilizers, organic sources of nutrients need to be applied
at higher volumes per land area or amended with inorganic fertilizers sources as
suggested by Singh et al. (2008) and Arancon et al. (2006). However, organic
fertilizers have other extra benefits such as improving soil physical, chemical and
biological properties, slow release of nutrients, reducing physiological disorders in
vegetables and being environmentally friendly if properly managed, compared to
inorganic fertilizers (Singh et al. 2008; Das et al. 2016). As a solution to the low
nutrient content of organic fertilizers, several researchers have looked at the potential
of amending vermicomposts with other nutrient-rich inorganic materials (Kumar and
Singh 2001). One important macronutrient whose concentration can be enhanced
through amending vermicomposts with inorganic materials is phosphorus (P), and
this has been the subject of several studies (Bhattacharya and Chattopadhyay 2002;
Edwards et al. 2010; Adhami et al. 2014).
Apart from nitrogen, phosphorus is the most important plant nutrient that plays
critical roles in almost all major bio-chemical processes within plants such as
photosynthesis, energy transfer and molecular biosynthesis (Roy 2017; Sharma
18 Some Perspectives on Vermicompost Utilization in Organic Agriculture
309