CHAPTER - 2
REVIEW OF LITERATURE
2.1 The ecological functions of earthworms
In temperate regions, earthworms such as those in the family Lumbricidae are well
known to improve soil macroporosity and aggregation, and to increase nutrient and organic
matter cycling (Lee, 1985; Vetter et al., 2004). They are considered 'ecological engineers',
organisms that create physical structures and modify the availability or accessibility of
resources for other organisms (Jones et al., 1994). Macronutrients are therefore abundant
around earthworm casts and burrows; root growth is particularly enhanced in this area of the
soil (Edwards and Bater, 1992). Earthworms make a similar contribution to soil fertility in
tropical soils, sharing this niche with soil feeding termites (Fragoso and Lavelle, 1992), ants
and other soil fauna.
Earthworms are often grouped according to their physical appearance (body color,
shape and size) and ecological functions such as burrowing abilities and food preferences
(Bouché, 1977). This permits researchers to categorize earthworms in ecological classes, as
epigeic, anecic and endogeic earthworms. Epigeic earthworms are small and live in the litter
layer, typically ingest litter and humus without mixing organic and inorganic materials
extensively (Lavelle, 1988). Anecics are large deep burrowing worms that come to surface
when it is time to feed whereas endogeics live near the surface of soils in the organic
horizons while producing horizontal galleries (Paoletti, 1999). Epigeics are typically found in
the upper litter layer of the soil, endogeics in the first 10 to 20 cm and anecics in the deeper
recesses of the soil. Anecic species are generally sparse in the tropical environment (Barois et
al., 1999). Additional categories have been created to include the coprophagics, which live in
manure piles and the arboricolous earthworms that live in suspended soils of humid tropical
15
forests (Paoletti, 1999). Arboricolous are similar to epigeics, have large cocoons and can
withstand long periods immersed in water, especially in pools of water that accumulate in
bromeliads in the cloud forests.
In the tropics, earthworm communities are influenced by a suite of hierarchical factors
with temperature dominating, followed by edaphic (nutrient status) and environmental
(seasonality) factors (Fragoso and Lavelle, 1992). Earthworm densities versus annual rainfall
follow a bell curve relationship in tropical rainforests, peaking at approximately 3000 mm of
rainfall (Fragoso and Lavelle, 1992). Rainforests with less than 2000 mm of rainfall are too
dry, whereas 4000 mm or areas with periodic flooding are too wet for earthworms. In arid
regions with temperatures above 35ºC, annual rainfall less than 900 mm and a dry season
longer than 5 months, termites are the dominant soil macrofauna and earthworms are rarely
found (Lavelle, 1988). However, earthworms can survive dry periods by migrating to deeper
soil layers, which leads to a seasonal change in the vertical distribution of earthworms
(Fragoso and Lavelle, 1992). Horizontal distribution is thought to be random and structured
at different spatial scales (Rossi, 2003; Decaëns and Rossi, 2001). Populations of earthworms
sampled from a grass savannah in Cote d'Ivoire were found in randomly distributed clusters
of variable size, suggesting a local influence was responsible for the observed pattern (Rossi,
2003).
Most of the information on earthworm ecology comes from studies in natural
ecosystems (forests, savannahs) and managed agroecosystems. However, the data on
earthworm abundance in urban ecosystems is sparse. Studies undertaken in temperate
regions, including New York City (Steinberg et al., 1997; McDonnell et al, 1997; Pouyat et
al.,1997), Baltimore-Washington Metropolitan Area (Csuzdi and Szlávecz, 2003), Stockholm
(Erséus et al., 1999) and London (Smith et al., 2006) reported higher earthworm abundances
with increasing urbanization. The authors attribute this to the anthropogenic introduction of
16
exotic species in urban centers (in the case of New York, the region has low earthworm
abundance and variety, a legacy of glaciation) and the island effect, which contributes to
higher temperatures in cities. Cities offer diverse habitats within a small area, another reason
for the high level of species richness in urban ecosystems (Rebele, 1994; Smith et al., 2006).
2.2 Role of earthworms in waste management
Soil fertility has become one of the most important jargons of a conventional
agronomist (Balaraman, 2005). This term has been directly correlated to fertilizers. The
traditional concept to evaluate the soil had been its quality or health. Soil health is a more
appropriate term as it reflects the entire system and not just the chemical status of the soil.
Soil health includes the physical and chemical characteristics of the soil and also the biotic
components of the soil. It is the “living” soil. Though multitudes of soil organisms are related
to soil health, earthworm is the pulse of the soil. Thus, healthier the pulse, healthier the soil
(http://www.erfindia.org/waste.asp).
Earthworms are generally called the biological indicators of soil fertility. Since they
support the healthy populations of bacteria, fungi, actinomycetes, protozoans, insects, spiders,
millipedes and a host of others essential for sustaining a healthy soil (Sharma, 2003).
Earthworms improve the soil in several ways. Earthworm acts as an aerator, crusher, mixer,
grinder, chemical degrader and biological stimulator in soil (Murugappan, 2005). They mix
organic matter with mineral soil, release nutrients and make available to the plants, aerate the
soil and improve infiltration of water through burrowing and contribute to the formation of
stable soil aggregates, producing the crumbly texture of a fertile soil by the intimate mixing
of organic matter, microorganisms, mineral soil and secretions from the worm skin and gut
(Ramesh et al., 2000). Earthworms are well known to help the soil in respiration, nutrition,
excretion and stabilization. They cause tunneling, show buffering action, regulate soil
17
temperature and thus stimulate useful activity of aerobic microorganisms (Kannaiyan and
Lilly, 1999).
Earthworms, the soil invertebrates, along with soil microorganisms carry out a
yeomen’s service of degrading organic waste materials and thus maintain the nutrient flux in
the system. Earthworms form a major component of the soil biota and together with a large
number of other organisms constitutes the soil community (Talashilkar and Dosani, 2005).
The chief source of food to the soil biota is the litter contributed by plants. Although the dead
plant tissues constitute the bulk of the food ingested by the earthworms, living
microorganisms, fungi, microfauna and mesofauna and their dead tissues are ingested as an
important part of the diet.
Earthworms have been on the earth for over 20 million years and have faithfully done
their part to keep the cycle of life continuously moving. Their purpose is simple but very
important (www.widener.edu). They are nature’s way of recycling organic nutrients from
dead tissues back to living organisms. The Egyptian Pharaoh, Cleopatra said, “Earthworms
are sacred”. She recognized the important role the worms played in fertilizing the Nile Valley
croplands after annual floods (http://www.unu.edu/env/plec/cbd/abstracts/ Kostecka.doc).
Earthworms play a major role in land reclamation by way of their high efficiency of
harvesting energy from a nutrient poor soil (Mani, 1999). Earthworms burrow deeply into the
mineral strata and return periodically, to cast faecal material at the soil surface facilitating the
transport of certain elements to the surface from deep in the profile. There is abundant
evidence that concentration of exchangeable calcium, sodium, magnesium, potassium and
available phosphorus and molybdenum are higher in earthworm casts than in the surrounding
soil (Kumar et al., 2000). Earthworms have been aptly named as the ‘Cinderellas of organic
farming (www.nripulse.com). The conversion of organic wastes in the form of vermicompost
is the major role played by the earthworm in nature. In the vermicompost, the secretions of
18
worms and the associated microbes act as growth promoters along with other nutrients. It
improves physical, chemical and biological properties of soil in the long run on repeated
application (Jayakumar et al., 2005).
Earthworms, besides producing enormous amount of worm casts over the years,
modify the structure of the soil. They act as ‘natural miniature factories’ (Kitturmath et al.,
2007). (Bhawalkar and Bhawalkar ,1993) designated earthworms as the ‘natural bioreactor’.
They play a key role in soil biology as versatile natural bioreactors. They effectively harness
the beneficial soil micro flora, destroy soil pathogens and convert organic wastes into
valuable products such as bio fertilizers, bio pesticides, vitamins, enzymes, antibiotics,
growth hormones and proteinous worm biomass (Sharma, 2003). Earthworms are the major
secondary decomposers. The manure formed from the dead tissues of plants and animals is
naturally the source of macro and micro nutrients in limited quantities. The weather
conditions and the soil type in the tropical countries do not favour the restoration of carbon
resource in the soils. The application of organic manure replenishes organic carbon to the
impoverished soils. The presence of high level of oxidisable organic carbon helps in the slow
release of nutrients from the manure and curbs the leaching of nutrients. This beneficial
activity is because of the nutrient availability (Gunathilagaraj et al., 2000).
Earthworms have occupied an important position in the ecosystem, that made the
famous biologist Charles Darwin conclude, “It may be doubted whether there are many other
animals which have played so important a part in the history of the world as have these lowly
organized creatures”(http://www.erfindia.org/waste_resource.asp). There can be little doubt
that humankind’s relationship with worms is vital and needs to be nurtured and expanded.
The following sections discuss on the most important areas in which our natural environment
can be preserved and sustained through a partnership with these engines of the soil.
Earthworms can also be described as microbioves as they are potentially important vectors of
19
microbial propagation and have been shown to influence plant fungal pathogens. Earthworms
live on the upper part of the soil profile and transport a large amount of (200 - 400 ha/yr) soil
through their bodies. They have been implicated in both reduction and dispersal of organisms
and spread a variety of beneficial microorganism such as Pseudomonas, Rhizobia and
Mycorrhizal fungi (Raja, 2004).
Earthworms, through a type of biological alchemy, are capable of transforming
garbage into ‘gold’ (http://www.dainet.org/livelihoods/default.htm). Worms are nature’s
garbage men, honing their waste devouring skills over the millennia to produce the perfect
organic waste disposal system. They live under the topsoil dragging down dead organic
matter from the surface to be recycled and harnesses natural recycling system. Earthworms
have been known as the ‘farmer’s friend’ and the ‘gardener’s manure factory’
(www.cityfarmer.org). Worms are not only the gardener’s best friend; they are also the
recycler’s as well. Nature’s little waste disposal experts have found a new place in ecoconscious household’s across the globe as more and more people are catching on to the idea
of
using
worms’
special
talents
to
dispose
their
organic
household
waste
(http://www.unu.edu/env/plec/cbd/abstracts/Kostecka.doc). Earthworms are useful not only
for making compost and waste management but also have a utility in the context of
developing countries as a ready reckon for knowing the soil health at farmer level. They are
one of the easily available biological indicators of soil activities and this natural facility need
to be used for monitoring and maintaining the biological health of the soil (Sharma, 2003).
There is no doubt that earthworms, ‘nature’s unpaid labor force’ have an important place in
the world as Charles Darwin claims. Recent studies have revealed that the intelligent use of
selected species of earthworms (especially in the ‘decomposer industry’) can produce
benefits to mankind in different ways with the help of vermitechnology (www.nripulse.com).
Earthworms are underground farmers who turn the soil over like a plough. They form a major
20
component of the soil system and have been efficiently ploughing the land for millions of
years and assisting in the recycling of organic nutrients for the efficient growth of plants
(Sharma, 2003). In just one acre there can be a million or more, eating ten tons of leaves,
stems
and
dead
roots
a
year
and
turning
over
40
tons
of
soil
into
vermicompost(www.webdirectory.com). It is noteworthy that earthworms can be used as
biological tools for rebuilding of the top-soil, at no cost to the farmers, in easy sustainable
soil management. Earthworms are also known as ‘earth-angels’ that can produce ‘heavenly’
humus (www.nripulse.com) and are considered as scavengers of land. They burrow in moist
soil and mud, feeding on decomposed plant materials and other organic matter (Prema and
Raja, 2004). Due to their burrowing and casting activities the earthworms turn over the soil
from bottom to the top.
It was estimated that 1800 worms which is an ideal population for one square meter
can feed on 80 tons of humus per year. Nature takes as much as 200 years to build up a ten
millimeter layer of humus rich soil. Given a proper supply of wastes, earthworms can achieve
the same result in a single year (Abbasi and Ramasamy, 2001). Earthworms inevitably
consume the soil microbes during the ingestion of litter and soil. It has been recently
estimated that earthworms necessarily have to feed on microbes, particularly fungi for their
protein or nitrogen requirement (Ranganathan.and Parthasarathi, 2000). The use of
earthworms in waste management is largely a straight forward process. All the earthworm
species have a specific range of environmental conditions and ecological requirements that
must be met to thrive. The most successful vermicomposting species are those with a fairly
broad range of tolerances (http://www. recycledorganics.com). Earthworms can ingest more
than their own body weight of organic matter each day while some species can process vast
quantities very rapidly given optimum conditions. This rate of ingestion is more commonly
observed to be between 50 to 100 per cent of worm biomass. Each earthworm weighs about
21
0.5 to 0.6 gram (http://www.vermico.com/summary.htm). However, the rate of ingestion is
largely dependent upon the species of earthworm, the maturity of individuals, the rate of
reproduction, the population densities and several feedstock variables, given optimum
environmental conditions (http://www. recycledorganics. com).
Earthworms play a major role in the breakdown of organic matter and in the cycling
of nutrients in natural ecosystems (Singaram, 2005). They are a part of a complex chain of
chemical, biochemical, biological and ecological interactions. Earthworm mouthparts are not
capable of chewing or biting and so rely on the decomposition of organic matter by
microorganisms such as bacteria, algae, fungi, nematodes, protozoa, rotifers and
actinomycetes, before they can ingest the softened material along with the microorganisms
(http://www.recycledorganics.com). Earthworms posses a grinding gizzard that fragments the
organic residuals (Edwards and Bohlen, 1996). Some other weeds for example, water
hyacinth have been successfully converted into vermicompost (Gupta, 2007). The authors
hypothesized that vermicomposting can be an alternate technology for the management of
parthenium weed.
The earthworm gut secretes mucus and enzymes that selectively stimulates beneficial
microbial species (Bhatnagar and Palta, 1996). Earthworms promote further microbial
activity in the residuals so that the faecal material or casts they produce, is much more
fragmented
and
microbially
active
than
what
the
earthworms
consumed
(www.nyworms.com/ vermicomposting.htm). Effectively, earthworms inoculate the soil or
organic matter, with finely ground organic residuals and beneficial microorganisms which
increase the rate of decomposition and enables further ingestion of microorganisms by
earthworms (http://www.recycledorganics.com). They crush the soil and the organic matter
and after consumption, the matter undergoes a complex biochemical process in its digestive
system which is excreted out in the form of granular casts of earthy smell (Mani, 1999).
22
Enhanced decomposition and nutrient mineralization are the most important and
critical factors where earthworms play a vital role and thereby increase the growth and
productivity of plants (www.lancasster.unl.edu). Earthworms transport minerals and subsoil
compounds from deep in the soil. In this process the earthworms transform these compounds
into nutrients that plants use much more readily. Earthworms help to increase the healthier
plants, more beautiful flowers, bigger and more luscious fruits and vegetables. Earthworms
are ancient and respected creatures in many cultures. The Chinese translation, earthworms is
‘Angels of the Earth’. Aristotle called them ‘The Intestines of the Soil’. The scientist, Charles
Darwin studied earthworms for more than 40 years in the last century. He said that worms are
the great promoters of vegetation, perforating and loosening the soil (NIIR, 2004).
Earthworms serve as prime fishing bait as a high protein and low cost cattle feed particularly
in Japan. They are also used as bioindicators of heavy metal contamination. They form an
important group of soil animals that are known to improve soil productivity by enhancing the
physical, chemical and biological characteristics of soil. They play a vital role in the
breakdown of dead plant and animal material and in soil structure aeration and fertility
(Prema and Raja, 2004). The tunnels made by the worms serve the purpose of air passage for
root growth and for drainage of water. Mucus containing worm casts absorb soil moisture and
nutrients for better crop production. Earthworms are considered as nature’s plough and
natural fertilizer manufacturers. They have played an important part in the history of mankind
in preserving fertility of the soil and thereby sustaining crop production. The only animal that
exclusively devoted itself to mass production is the earthworm (Venkataratnam, 1994).
Earthworm ensure ground water recharge and prevent run-offs causing soil erosion
and flash floods (Ganeche and Swaminathan, 2000). Chemical analyses of earthworm
castings show that they can contain upto two times as much available magnesium, five times
as much available nitrogen, seven times as much available phosphorus and eleven times as
23
much available potassium as the surrounding soil (Abbasi and Ramasamy, 2001). Earthworm
processes more than 20 per cent of the total energy input into the system; stimulate
composting activity by decreasing 25 per cent of the composting period. Earthworm is not
only the biofertilizing agent and composting element but also aerator, moisture retainer,
crusher, biological agent, nature’s best soil chemist and agriculturist (Mani, 1996).
Earthworms produce worm casts about 4 to 36 tonnes per acre and in terms of nitrogen it
comes to 20 to 180 kilo grams per acre per year and it is much more than the average need of
nitrogen for any crop (www.wormdigest.org).
The action of compost by worms prevents bad odours. They are quite unobstructive
and clean and the job they do is incomparable to anything else. They like to eat, and need
very little care to live. Worms create conditions that promote beneficial aerobic bacteria and
optimal composting conditions (Subash, 1998). Earthworms are nature’s cleanup crew, aiding
in the production of lush, humus rich top soil from spent plant and animal materials. These
elegantly efficient organisms have been on earth for hundreds of thousands of years longer
than humankind, largely untouched by evolution due to their perfect adaptation to their role
in nature. Earthworms form a major component of the soil system and these organisms have
been efficiently ploughing the land for millions of years and assisting in the recycling of
organic nutrients for the efficient growth of plants (Ramakrishnan, 2005). Earthworms can
minimize the pollution hazard caused by organic waste by enhancing waste degradation. The
ideal species of earthworms help to convert waste into wealth (www.wrangler.com).
Earthworms have long been described as the ‘intestine of the earth’ and ‘friends of the
farmers’, because of their manifold functions in the soil (Darwin, 1881). The role of
earthworms is breaking down of dead plant and animal residues in soil. “Nothing can be
compared with earthworms in their positive influence on the whole living nature. They create
soil and the lives in it. They are the most numerous animals on Earth and the main creatures
24
converting all the organic matter into soil humus providing soil’s fertility and biosphere’s
functions: disinfecting, neutralizing, protective and productive” (Igonin, 2004). (Gupta and
Garg, 2008; Kaur and Singh, 2010 have reported higher concentration of metals in final
vermicomposts as compared to initial metal level.
2.3 Vermicompost production
Several earthworm species are recommended for vermicomposting, such as the
corophragic earthworms E. foetida and Eisenia andrei (Dominguez et al., 2001). Another is
the epigeic E. eugeniae, a tropical earthworm with a high reproduction rate (Mba, 1983;
Gajalakshmi et al., 2001). The anecic L. mauritii (Tripathi and Bhardwaj, 2004) noted for its
ability to withstand environmental stresses, and the epiendogeic H. africanus have also been
recommended (Tondoh ,1998). These earthworms are capable of consuming a wide range of
organic substrates from sewage sludge, animal wastes; crop residues (water hyacinth, mango
leaves) to industrial refuse (Atiyeh et al., 2000). They rapidly convert the wastes, through a
non-thermophilic process, into a humus-like substance with smaller particle size than the
starting material (Arancon et al., 2003; Edwards and Burrows, 1988). (Gajalakshmi and
Abbasi, 2004) observed an increase in vermicast output as various earthworms (E. euginiae,
L. mauriti and P. excavatus) acclimatized to the feed, gained weight and bred. A similar trend
was observed in H. africanus (Tondoh ,1998), although earthworms collected from the field
had a lower survival rate than those hatched in the laboratory.
In the conventional vermi-reactor, 50% of the reactor volume is occupied by
successive layers of sawdust (1 cm), river sand (2 cm) and garden soil (4 cm) (Gajalakshmi et
al, 2001; Jain et al., 2003). This design does not make full use of the reactor volume and it
has been suggested that a modified vermi-bed, consisting of a single layer of moistened thick
cotton cloth at the base of the feed, should be used for a four-fold increase in efficiency (Jain
25
et al., 2003, Gajalakshmi et al., 2005). Though many potential pollution hazards are reduced
during vermicomposting, some contaminants, labile nitrogen, phosphorous, sulfur
compounds and potassium can leach, or be translocated by earthworm activity, into the
bottom layers of the vermi-reactor (Mitchell, 1997). Large scale vermicomposting operations
therefore require a highly absorptive or impermeable medium at the base of the reactor
volume to contain nutrient leaching and other uncontrollable releases into the environment
(Mitchell, 1997).
The effect of temperature on the earthworm life cycle was evaluated by growing E.
eugeniae and E. fetida in dishes (12.5 cm diameter, 5 cm deep) containing 200 g of separated
cattle solids with 82% moisture content(Dominguez et al., 2001). Earthworm cocoons
reached sexual maturity most quickly when the temperature was 25 to 30 oC, regardless of the
population density. The same study also observed that some E. eugeniae perished at 30ºC, but
E. fetida withstood higher temperatures. (Tripathi, 2003) nevertheless recommended using a
substrate with 70% moisture content and a pH of 6.5 and a temperature of 25 oC as optimal for
E. fetida growth and development. The same authors recommended a substrate with 60%
moisture content, pH 7.5 and a temperature of 30oC as optimal for breeding L. mauritii. They
also indicate that the maximum vermicomposting rate was related to earthworm biomass per
unit waste, rather than the total number of earthworms. Earthworm biomass growth is slower
in densely populated vermi-reactors, explaining why the cast output rates per earthworm are
lower in high density vermi-reactors than in low-density reactors (Jain et al., 2003;
Gajalakshmi et al., 2005). (Gajalakshmi, 2001) nevertheless observed higher cast output rates
per reactor volume in high-density vermi-reactors than in low-density vermi-reactors
operating over the same period.
26
2.4 Field application
Russel(1909) first reported on the effect of earthworms on soil productivity. Hopp and
Slater (1949) were the first to quantify the importance of earthworm application to crop yield.
(Nijhawan and Kanwar, 1952) have studied the physico-chemical properties of earthworm
casting and their effect on the soil productivity. They also pointed out the impact of
vermicompost upon wheat seedlings. (Gavrilov, 1962) made an intensive study on the role of
earthworms in soil enrichment by the usage of biological
active substance and found the
deposition of plant growth factors by the earthworms. Neilson(1965) deduced the plant
growth substances in earthworms and found its similarity to the growth hormone IAA (Indole
Acetic Acid). (Atlavinyte and Daciulyte, 1969) have reported the accumulation of Vitamin
B12 in the soil. Eitminaviciute et al., 1971) related the concentration of vitamin B12 to the
soil, animal and microbial populations. The effects of earthworm cast on ryegrass seedlings
were reported by (Springett and Syers, 1979). (Graff and Makeschin, 1980) reported the
release of the yield influencing substances by earthworms into soil. (Mc Coll et al., 1982)
found that the earthworm humic matter improved the seed germination and enhanced plant
nutrient absorption capacity and vitamin content of plants. The earthworm casting in plant
propagation was reported by (Grappelli et al., 1985), cultured E. eugeniae for cast production
and assessed worm cast as biofertilizer. The effect of cast of Pheretima alexandi on the
growth of Vinca rosea and Oryza sativa were reported by (Reddy, 1988).
An increase in soil productivity, which cannot be explained by mineral nutrients
alone, is often recorded when composted organic wastes are supplied to croplands. This is
the so-called "organic matter effect" suggests that mechanisms other than simple nutrient
supply can contribute to plant growth (Galli et al., 1992). The effect of peat moss-shrimp
wastes compost on barley (Hordeum vulgare L.) applied alone or with NPK effect of
compost on straw yield, numbers of tillers, plant height, and number of ears was more
27
important than that of fertilizer. Compost was considered incomplete as a fertilizer when
composted green yard and landscape waste and peat were evaluated as to plant nutrient
supply.
Both were mixed with per liter and added to pots planted with tomatoes and
marigolds at a volume ratio of 1:1. Compost was equivalent or superior to peat in plant
growth and it contributed to crop macronutrient nutrition, but the highest fertigation rate was
required for optimum growth. When deciduous ornamental shrubs were grown in 33%, 67%,
and 100% of three different sources of compost, despite large variation in species, growth
response to sources and levels of compost, are equally well or better in the compost-amended
regimes than in the control and were influenced little, or not at all, by initial or prevailing salt
levels in the media. Shoot and root dry weight of some plants increased with increasing
compost levels. The reverse relationship occurred (all sources) in shoot and root dry weight
of privet and root dry weight of weigela and potentilla. Leaf nutrients (N, P, K, Ca, Mg, Fe,
Mn, and Zn) tended to increase with increasing compost levels, but not all species showed
this response with all nutrients. Regardless of compost source or level, all shrubs were of
marketable quality when harvested, except privet, which showed leaf chlorosis in all
compost-amended regimes. The efficiency of organic nitrogen uptake from organic fertilizers
varies with the type of fertilizer, and organic nitrogen sources can cause short-term crop yield
decreases. 10-30% of N was taken up when poultry manure or pea vine residues were added.
(Lavelle et al., 1992) found a release of large amount of nutrients from the freshly
deposited cast of earthworms. A significant increase in maize production by 36% was
observed due to earthworm inoculation (Pashanasi et al., 1996). A reduction by 50% of the
recommended dose of nitrogen was supplemented by the use of vermicompost as organic
manure was reported by Jadhav, (1996). Chakrabarti et al., (1998) found compost as one of
the principle ingredients of a balanced growth medium. The stimulatory effects of earthworm
body fluid on crinkle red variety of Anthurium andreanum was studied by Karuna et al.,
28
(1999). Increase of nutrients level indicated that parthenium can be a raw material for
vermicomposting if mixed with cowdung in appropriate quantity (Anoop yadav and Garg
2011).
2.5 Nutrient dynamics in compost and earthworm casts
Of late, much emphasis has been paid globally on organic farming with large-scale
use of organic manures and biofertilizers. Acute shortage of conventional organic manures
like animal dung also necessitates the exploitation of other sources of organic manures. Weed
biomass is one of the easily available sources of organic matter and plant nutrients, which
hitherto, have not received required attention. The favorable climatic condition of the
Southern Western Ghats region in general and Courtallam in particular, leads to the
production of huge weed biomass of diverse species composition both in cropped and noncropped areas. Most of the total N was in organic forms; NH4 was more abundant than NO3,
and calcium was the most abundant nutrient followed by K, Na, Mg and P. Most of the Ca
and Na were in available forms; available K and Mg were lower and available P was very
small (Villar et al., 1993).
On the other hand, NH4 levels are high in fresh earthworm casts but casts stabilize
after 2 weeks of aging through nitrification. The pH level in casts is slightly low, which could
reduce denitrification. In fresh casts, NH4 levels were very high (294.2-233.98 µg g-1 dry
cast) due mineralization in the earthworm gut. During the first week of cast aging, NH4 levels
decreased while NO3 levels increased, due to rapid nitrification in the fresh casts. After two
weeks, the levels of NH4 and NO3 were stabilized, probably due to organic matter protection
in dry casts (Decaen et al., 1999). Casts tend to stabilize through nitrification after being
deposited in a garden soil processed by earthworm. Ammonium underwent complete
nitrification compared with 33 and 9% nitrification in loam and cast aging (+100%), possibly
29
because of CO2 fixation or macro faunal activities in casts. Stabilized earthworm casts
leached less dissolvable organic carbon than from undigested soil. Nutrient losses from casts
that underwent several wetting / drying cycles show that there was a strong protection of
nutrients in casts at first, but this was reduced as the aggregate structure was weakened
(McInerney and Bolger, 2000). After a 20 days long incubation of fresh casts a rapid increase
in mineral N was observed during the first few days after deposition, and then a decrease to a
level 4.5 times higher than in the soil. Also the NH4 level was higher in fresh casts than in the
control (Rangel, et.al., 1999). The decrease of mineral N in time in casts can be due to N
becoming microbial biomass, volatilized, denitrified, or leached (Lavelle, et.al., 1992). In
(Haynes, et.al., 1999) un-ingested soil and casts were incubated for 42 days, and extractable
P levels were similar in casts and soils during the initial stages of incubation, but were larger
in casts after 28 and 42 days. Activities of arylsulphatase and acid phosphates were lower in
casts than in un-ingested soil; therefore the mineralization of organic matter during gut transit
could be the reason for the increase in extractable P and S during incubation. (Haynes, et.al.,
1999) concluded that mineral N increases because of mineralization in the gut, but P and S
levels increase due to mineralization after egestion. In (Lavelle, et.al., 1992) mineral N in
casts was mostly in the form of ammonium, and after a 26 days long incubation NH4 was
nitrified or immobilized in biomass. The incubation of soil before ingestion increased NH4
production in casts and being slightly acidic, casts do not favor the denitrification of NO3.
Biomass N was stable (relatively) after an initial flush on day one. Suthar (2009) reported that
the earthworm cast is one of the most useful and active agent in introducing suitable
chemical, physical and microbial changes in soils and thereby directly increase the soil
fertility and crop production.
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2.6 Microbiology
Soil is an appropriate environment for the development of eukaryotic (algae, fungi,
bacteria) as well as prokaryotic (bacteria and archeas) microorganisms. Virus and
bacteriophages are also present. All these organisms establish relationship among themselves
in highly varied and complex ways which contributes to soil characteristics because of their
role in the modification of solid, liquid and gaseous stages.
One of the first forefathers on microbial presence in the digestive system was Parle
(1963) who reported bacterial, fungal and actinomycetic population in three species of
earthworms; Lumbricus terrestres, Allolobophora caliginosa and A. longa. A study carried
out by Kristufek et al., (1994) found population of bacteria, actinomycetes, and fungi sterile
mycelium and plant cells in soil however within the intestines of the earthworms Lumbricus
rubellus these organisms were found lysate except for a few actinomycetes, endospores and
encapsulated bacteria. On the other hand (Marialigeti, 1979) found that the microbial flora
within the posterior segment of the intestine of E. lucens contained 473 microorganisms
where 73% pertain to the genus Vibrio.
Contreas,(1980) reported that 70% of flora in the intestine of E. lucens was
represented by only one species of actinomycete, Streptomyces lipmanii an organism rarely
found in nature. Dash et al.,(1986) did a microfungal characterization in the digestive tract of
the three species of earthworms (Octochaetone surensis, L. mauritii and Drawida Willsi)
found in the tropical zones of India and identified 18 species of fungi from genuses
Aspergillus, Penicillium, Thielavia, Botryotrichum, Fusarium, Rhizopus, Curvularia,
Chaetomium and Trichoderma. Four more genuses namely Neocosmospora, Cladosporium,
Syncephalastrum and Actinomucor were found in L. mauritii unlike the other two species of
earthworms. It is important to mention that the digested material for all three species came
from organic waste.
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Kristufek et al.,(1992, 1993) observed and increase in the number of bacteria,
actinmycetes and fungi in the anterior section of the digestive tract of Lumbricus rubellus
while the opposite occurred in Aporrectodea caliginosa and A. caliginosa. The Actinomycete
community present in the intestine of E. fetida, mainly Streptomyces caeruleus develops
better in the intestine in comparison to soil and helps the earthworms to metabolize organic
matter and decomposition of substances from plant origin. Earthworm activity is known to
influence nutrient availability, microbial activity and physical properties of soil (Edwards and
Bohlen, 1996). Soil microbial activity is stimulated during gut transit and the resulting
increase in mineralization rate can result in much greater nutrient availability (particularly
that of N, P and S) in cast than in soil (Blair et al., 1995). Preferential ingestion of fragments
of decaying plant material with a high nutrient content also contributes to the greater nutrient
availability in casts (Lee, 1985). Earthworms mechanically mix mineral particles and organic
matter through their digestive system which carries out disintegration, grinding and digestion
of the ingested material, increasing or decreasing the activity and number of beneficial or
pathogenic microorganisms (fungi, actinomycetes and bacteria) (Winding et al., 1997).
The work of Egert, et.al.,(2004) addressed bacterial and archaeal community
structures in soil, gut, and fresh casts of L. terrestris using terminal-restriction fragment
length polymorphism (T-RFLP) analysis of 16S rRNA gene fragments. The species E. fetida
may establish a symbiotic relationship with bacteria from the genus Acidovirax given that
these bacteria form nodules in the ampoules of the nephridium of the earthworms and help in
the process of protein decomposition (Davidson and Stahl, 2006). On the other hand, ValleMolinares
et
al.,(2007)
identified
seven
species
of
bacteria
from
the
genus
Bacillus: (B. insolitus, B. Megaterium, B. brevis, B. pasteurii, B. sphaericus, B. thuringiensis
and B. pabuli) within the intestine of Onychochaeta borincana. All these species are typical
soil bacteria. In addition, it was found that the microbial weight of the intestinal region
32
decreased from the anterior to posterior section. Additionally, it was observed that some
bacteria increased in the posterior section of the intestine, may be because for a many bacteria
this portion presents adequate conditions for their development. The participation of
microorganisms within the digestive tracts of earthworms is of great importance given that a
lot of these are involved in the degradation of organic matter (Byzov et al., 2007). For studies
on bacteria within the intestines of earthworms, diverse methods and techniques have been
used which have helped in identifying species of the genus Bacillus, Pseudomonas,
Klebsiella, Azotobactor, Serratia, Aeromonas and Enterobacter (Valle-Molinas et al., 2007;
Byzov et al., 2007; Singleton et al., 2003).
33