et al. 2013). Although P is abundant in soils, it is mostly insoluble and precipitated in
different forms which are not easily available for plant uptake (Sharma et al. 2013).
Due to this, available P levels in soils have to be supplemented in most agricultural
soils by adding chemical P fertilizers to improve crop productivity, which represents
a major cost in agriculture and poses great environmental risks (Alamgir et al. 2012).
The economic and environmental challenges associated with the use of chemical P
fertilizers such as eutrophication and diminishing P reserves have resulted in a
renewed interest in alternative sources of P like phospho-composts (Alamgir et al.
2012). Recent research has focused on two inorganic materials that have been shown
to have potential in improving the phosphorus nutrition of organic vermicompost,
namely rock phosphate (Kumar and Singh 2001; Aria et al. 2010; Busato et al. 2012)
and fly ash (Malik and Thapliyal 2009; Bhattacharya et al. 2012; Mupambwa et al.
2015). What has created this interest is the high total P content within fly ash and
rock phosphate, which can be converted into bioavailable forms through processes
like vermicomposting. Phosphate rock or rock phosphate is a term that describes any
naturally occurring geological material that contains high concentrations of phosphate bearing minerals with a phosphate content of 15–20% (Edwards et al. 2010).
There are various types of these rock phosphates with varying chemical, mineralogical and physical properties depending on origin (Van Kauwenbergh 2010). Fly ash,
on the other hand, is a product of coal combustion, which is captured through
electrostatic precipitators at thermal power stations, and there are different types
depending on the origin of the coal materials (Mupambwa et al. 2015; Ukwattage
et al. 2013).
Apart from inorganic materials that are being promoted as amendments, biochar,
which is a highly aromatic product of pyrolysis, has recently received great interest
as highly stabilized organic additive for vermicomposting. Lehmann et al. (2006)
reported that biochar was shown to yield high aromatic materials with high stability
when added to soil and that it enhances the carbon sequestration potential of
vermicomposts, thus mitigating climate change. Different biochar qualities can be
produced from different feedstock and pyrolysis temperature (Zhao et al. 2013).
Barthod et al. (2018) indicated that higher pyrolysis temperatures during biochar
preparation leads to greater aromatization of the material, decreasing its surface area,
cation exchange capacity and content of volatile compounds. Biochar has a potential
to enhance vermicompost microbial activity due to its porous structure through
moisture and aeration control. However, biochar application rate higher than
20% is not recommended since it may hinder organic matter biodegradation.
Research is required to identify the optimum biochar amendment rate for different
vermicomposts (Xiao et al. 2017).
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H. A. Mupambwa et al.
different forms which are not easily available for plant uptake (Sharma et al. 2013).
Due to this, available P levels in soils have to be supplemented in most agricultural
soils by adding chemical P fertilizers to improve crop productivity, which represents
a major cost in agriculture and poses great environmental risks (Alamgir et al. 2012).
The economic and environmental challenges associated with the use of chemical P
fertilizers such as eutrophication and diminishing P reserves have resulted in a
renewed interest in alternative sources of P like phospho-composts (Alamgir et al.
2012). Recent research has focused on two inorganic materials that have been shown
to have potential in improving the phosphorus nutrition of organic vermicompost,
namely rock phosphate (Kumar and Singh 2001; Aria et al. 2010; Busato et al. 2012)
and fly ash (Malik and Thapliyal 2009; Bhattacharya et al. 2012; Mupambwa et al.
2015). What has created this interest is the high total P content within fly ash and
rock phosphate, which can be converted into bioavailable forms through processes
like vermicomposting. Phosphate rock or rock phosphate is a term that describes any
naturally occurring geological material that contains high concentrations of phosphate bearing minerals with a phosphate content of 15–20% (Edwards et al. 2010).
There are various types of these rock phosphates with varying chemical, mineralogical and physical properties depending on origin (Van Kauwenbergh 2010). Fly ash,
on the other hand, is a product of coal combustion, which is captured through
electrostatic precipitators at thermal power stations, and there are different types
depending on the origin of the coal materials (Mupambwa et al. 2015; Ukwattage
et al. 2013).
Apart from inorganic materials that are being promoted as amendments, biochar,
which is a highly aromatic product of pyrolysis, has recently received great interest
as highly stabilized organic additive for vermicomposting. Lehmann et al. (2006)
reported that biochar was shown to yield high aromatic materials with high stability
when added to soil and that it enhances the carbon sequestration potential of
vermicomposts, thus mitigating climate change. Different biochar qualities can be
produced from different feedstock and pyrolysis temperature (Zhao et al. 2013).
Barthod et al. (2018) indicated that higher pyrolysis temperatures during biochar
preparation leads to greater aromatization of the material, decreasing its surface area,
cation exchange capacity and content of volatile compounds. Biochar has a potential
to enhance vermicompost microbial activity due to its porous structure through
moisture and aeration control. However, biochar application rate higher than
20% is not recommended since it may hinder organic matter biodegradation.
Research is required to identify the optimum biochar amendment rate for different
vermicomposts (Xiao et al. 2017).
310
H. A. Mupambwa et al.