19.4 Earthworm Communities and Soil Physico-Chemical
Properties
19.4.1 Moisture
Earthworms are the soil invertebrates that have very little protection against the
fluctuations in moisture (Edwards and Bohlen 1996). The diversity, abundance and
biomass of earthworm species at a particular site are principally dependent on soil
moisture (Perreault and Whalen 2006; Mariotte et al. 2016). The body of earthworm
consists of 75–90% water, which helps them to respire due to the cutaneous
respiration mechanism. So, moisture is the critical factor for earthworm survival
and its activity in soil is also influenced by soil moisture (Edwards and Bohlen 1996;
Dewi and Senge 2015). If the soil is dry, then earthworms move to the deeper layers
of the soil or revert to diapause stage, during which earthworms roll their body in a
knot with slimy substance lined over the same which avoids moisture loss (Whalen
2004; Mariotte et al. 2016). The anecic earthworm species makes permanent vertical
burrows within the soil and also has the ability to enter into a true diapause stage
during the dry period (Mariotte et al. 2016). This downward movement of earthworm due to less soil moisture makes sampling more difficult including with
extraction solution such as formalin and allyl isothiocyanate. During the dry summer
season, earthworm with epigeic ecological category was more effected due to less
moisture availability on the upper surface, while on the other hand, endogeic species
have the ability to live deep in the soil and can get required moisture (Eggleton et al.
2009). The high level of moisture is also harmful to the earthworms and even also
caused death due to excessive water logging (Duiker and Stehouwer 2008). The high
moisture level also moistens the soil which affects the nutrient status of the soil and
hence affects the earthworm species (Fragoso and Lavelle 1992; Briones and
Schmidt 2017). The high moisture in the soil also has a compact structure with
poor aeration which also has a negative effect on the earthworm population (Birkas
et al. 2004; Capowiez et al. 2009). The requirement of moisture for earthworms
varies from species to species and each species has its own moisture requirements for
earthworm populations from different regions of the world (Dewi and Senge 2015).
For example, Aporrectodea caliginosa goes into the diapauses stage as moisture in
the soil goes below 25–30% in Europe (Edwards and Bohlen 1996). On the other
hand, in Argentina, Aporrectodea caliginosa remains active in the soils with moisture content as low as 15% (Ljungstrom et al. 1973). Zaller and Arnone (1999)
studied the activity of earthworm in the soil with different earthworm density and
moisture conditions (ambient and additional rain). The activity of earthworms was
measured on the basis of cast production by the earthworms. They observed that
vermicast production was increased with increasing earthworm density with ambient
moisture conditions. But as additional rain was given to the earthworm, there was no
increase in cast production and above-ground biomass which was due to a decrease
in earthworm density below the ground due to the increase in moisture level.
According to Ivask et al. (2006), soil moisture has a strong influence on the
340
S. Singh et al.
Properties
19.4.1 Moisture
Earthworms are the soil invertebrates that have very little protection against the
fluctuations in moisture (Edwards and Bohlen 1996). The diversity, abundance and
biomass of earthworm species at a particular site are principally dependent on soil
moisture (Perreault and Whalen 2006; Mariotte et al. 2016). The body of earthworm
consists of 75–90% water, which helps them to respire due to the cutaneous
respiration mechanism. So, moisture is the critical factor for earthworm survival
and its activity in soil is also influenced by soil moisture (Edwards and Bohlen 1996;
Dewi and Senge 2015). If the soil is dry, then earthworms move to the deeper layers
of the soil or revert to diapause stage, during which earthworms roll their body in a
knot with slimy substance lined over the same which avoids moisture loss (Whalen
2004; Mariotte et al. 2016). The anecic earthworm species makes permanent vertical
burrows within the soil and also has the ability to enter into a true diapause stage
during the dry period (Mariotte et al. 2016). This downward movement of earthworm due to less soil moisture makes sampling more difficult including with
extraction solution such as formalin and allyl isothiocyanate. During the dry summer
season, earthworm with epigeic ecological category was more effected due to less
moisture availability on the upper surface, while on the other hand, endogeic species
have the ability to live deep in the soil and can get required moisture (Eggleton et al.
2009). The high level of moisture is also harmful to the earthworms and even also
caused death due to excessive water logging (Duiker and Stehouwer 2008). The high
moisture level also moistens the soil which affects the nutrient status of the soil and
hence affects the earthworm species (Fragoso and Lavelle 1992; Briones and
Schmidt 2017). The high moisture in the soil also has a compact structure with
poor aeration which also has a negative effect on the earthworm population (Birkas
et al. 2004; Capowiez et al. 2009). The requirement of moisture for earthworms
varies from species to species and each species has its own moisture requirements for
earthworm populations from different regions of the world (Dewi and Senge 2015).
For example, Aporrectodea caliginosa goes into the diapauses stage as moisture in
the soil goes below 25–30% in Europe (Edwards and Bohlen 1996). On the other
hand, in Argentina, Aporrectodea caliginosa remains active in the soils with moisture content as low as 15% (Ljungstrom et al. 1973). Zaller and Arnone (1999)
studied the activity of earthworm in the soil with different earthworm density and
moisture conditions (ambient and additional rain). The activity of earthworms was
measured on the basis of cast production by the earthworms. They observed that
vermicast production was increased with increasing earthworm density with ambient
moisture conditions. But as additional rain was given to the earthworm, there was no
increase in cast production and above-ground biomass which was due to a decrease
in earthworm density below the ground due to the increase in moisture level.
According to Ivask et al. (2006), soil moisture has a strong influence on the
340
S. Singh et al.