Novus Natural Science Research
2012, Vol. 1, No. 1
Vermicomposting and its importance in improvement of soil nutrients and
agricultural crops
P.Saranraj* and D.Stella
Department of Microbiology, Annamalai University, Annamalai Nagar, Chidambaram – 608 002.
___________________________________________________________________________
ABSTRACT
The tremendous increase in population, urbanization, industrialization and agricultural production
results in accumulation quantities of solid wastes. This has created serious problem in the
environment. In order to dispose this waste safely it should be converted effectively. This is
achieved by bio-composting and vermicomposting of farm, urban and agro-industrial waste. It is
being increasing realized that composting is an environment friendly process, convert wide variety
of wastes into valuable agricultural inputs. Compost is excellent source of humus and plant
nutrients, on application of which improve soil biophysical properties and organic matter status of
the soil. This present review focused on vermicomposting and its importance in improvement of
soil nutrition and agricultural crops. This review assesses the following topics: vermicomposting,
raw materials of vermicomposting, microbiology of vermicomposting, effect of vermicompost
materials in agriculture and physico-chemical properties of soil, and importance of vermicompost.
Recycling organic wastes through vermicomposting is being considered as an economically viable
solution. Earthworms are considered as natural bioreactors while proliferate along with other
microorganisms and provide required conditions for the biodegradation of wastes
Key words: Composting, Vermicomposting, Earthworm, Organic wastes, Soil nutrients and
Agricultural crops.
INTRODUCTION
*Corresponding author: P.Saranraj
Department of Microbiology, Annamalai University,
Annamalai Nagar, Chidambaram – 608 002.
E.mail: microsaranraj@gmail.com
Composting, generally defined as the biological aerobic transformation of an organic byproduct into a different organic product that can be added to the soil without detrimental
effects on crop growth [1]. In the process of composting, organic wastes are recycled into
stabilized products that can be applied to the soil as an odorless and relatively dry source of
organic matter, which would respond more efficiently and safely than the fresh material to
soil organic fertility requirements. The conventional and most traditional method of
composting consists of an accelerated biooxidation of the organic matter as it passes through
a thermophilic stage (45° to 65°C) where microorganisms liberate heat, carbon dioxide and
water. However, in recent years, researchers have become progressively interested in using
another related biological process for stabilizing organic wastes, which does not include a
thermophilic stage, but involves the use of earthworms for breaking down and stabilizing the
organic wastes.
Composting is a biotechnological process by which different microbial communities convert
organic wastes into a stabilized form. During the process, thermophilic temperatures arise
because of the heat released due to biological activity. These temperatures are responsible for
pathogen inactivation. Composting is an aerobic process that requires oxygen, optimal
moisture and enough free air space and C/N ratio within certain limits. The treatment by
composting leads to the development of microbial populations, which causes numerous
physicochemical changes within mixture. These changes could influence the metal
distribution through release of heavy metals during organic matter mineralization or the metal
solubilization by the decrease of pH, metal biosorption by the microbial biomass or metal
complexation with the newly formed humic substances (HS) or other factors.
VERMICOMPOSTING
Earthworms are often referred to as farmer’s friends and natures ploughmen. Earthworms are
extremely important in soil formation, principally through their activities in consuming
organic matter, fragmenting and mixing it intimately with mineral particles to form
aggregates. During their feeding, earthworms promote microbial activity greatly, which in
turn accelerates the breakdown of organic matter and stabilization of soil aggregates. The
ability of some earthworms to consume a wide range of organic residues such as sewage
sludge, animal wastes, crop residues, and industrial refuse has been fully established. In the
process of feeding, earthworms fragment the waste substrate, enhance microbial activity and
the rates of decomposition of the material, leading to a composting or humification effect by
which the unstable organic matter is oxidized and stabilized. The end product, commonly
termed vermicompost and obtained as the organic wastes pass through the earthworm gut, is
quite different from the parent waste material.
Vermicomposting is a simple biotechnological process of composting, in which certain
species of earthworms are used to enhance the process of waste conversion and produce a
better end product. Vermicomposting differs from composting in several ways [2]. It is a
mesophilic process, utilizing microorganisms and earthworms that are active at 10–32°C (not
ambient temperature but temperature within the pile of moist organic material). The process
is faster than composting because the material passes through the earthworm gut, a significant
but not yet fully understood transformation takes place, whereby the resulting earthworm
castings (worm manure) are rich in microbial activity and plant growth regulators, and
fortified with pest repellence attributes as well in short, earthworms, through a type of
biological alchemy are capable of transforming garbage into ‘gold’ [3].
Vermicompost are finely divided peat-like materials with high porosity, aeration, drainage,
and water-holding capacity. They have a vast surface area, providing strong absorbability and
retention of nutrients. Vermicompost contain nutrients in forms that are readily taken up by
the plants such as nitrates, exchangeable phosphorus, and soluble potassium, calcium, and
magnesium. Decomposition of various organic substrates (kitchen waste, agro-residues,
institutional and industrial wastes including textile industry sludge and fibers) into valuable
vermicompost has been extensively studied using an exotic earthworm species (epigeicEisenia foetida) [4]. Tests have also been conducted combining thermo-composting and
vermicomposting to improve efficiency and compost quality [5].
Khaliq et al. [6] advocate the integrated use of organic and inorganic nutrient sources with
effective microorganisms (EM) for improving crop yield. The effects of earthworm processed
sheep-manure (vermicompost) on the growth, productivity and chemical characteristics of
soybean straw (Glycine max L. Merril.), wheat straw (Triticum aestivum L.), maize stover
(Zea mays L.), chickpea straw (Cicer arietinum L.), city garbage and greenhouse tomatoes
(Lycopersicum esculentum) has also been studied. Earthworm species such as Eudrilus
eugineae are voracious feeders of organic wastes, and their presence has been found to
reduce the time required for composting.
Raw materials for vermicomposting.
The residues like sugarcane trash, press mud, sugar factory effluent, broiler ash, spent wash,
etc, should be bio processed and added to the soil, to complete their natural cycle. Bicycling
of these residues through vermiculture biotechnology reduces the use of chemical fertilizers
derived from non-renewable sources. Venkatachalaiah [7] developed the method for
collecting, transporting and composting vegetable and fruit wastes. “BIOAGRO” compost
was produced from the city garbage. By the addition of neem cake, rock phosphate and
gypsum in small quantities to this compost “BIOAGRORICH” compost were made. Organic
wastes such as poultry manure, cattle dung, pig manure as well as agricultural waste like
sugarcane trash were fed to earthworm to hasten the process of decomposition.
Karthikeyan et al. [8] reported that the waste consist of decomposable organic matter with
high carbon nitrogen ratio. Hence the organic matter wastes are composed by
vermicomposting process in order to convert the organic waste into bio-compost. Swati
Pattnaik and Vikram Reddy [9] reported that the vegetable market waste is leftover and
discarded rotten vegetables fruits and flowers in the market. This urban waste can be
converted to a potential plant nutrient enriched resource compost and vermicompost that can
be utilized for sustainable land restoration practices.
Microbiology of vermicomposting.
Due to inoculation of microorganisms the period of composting was reduced by about 4
weeks. The results also indicate that by utilizing mesophillic cellulolytic fungi, the process of
composting a high C/N homogenous material can be accelerated and the quality of the
resulting composting can be improved. Various studies also indicated the possibility of
augmenting the quality of compost through inoculation with Azotobacter and phosphate
solubilizing microorganisms in the presence of rock phosphate [10].
Edward et al. [11] studies the symbiotic interaction between earthworms and microorganisms
in the breakdown and fragment organic matter progressively. The role of earthworms as
vectors of beneficial soil bacteria and their capacity of influence the population dynamics and
impact of microorganisms on soil and plants was studied. Actinomycetes and bacteria (both
celluloolytic and lignolytic) which are important in waste degradation increase exponentially
along the entire length of the tabular bioreactor.
The gut isolates included the Actinomycetes, Streptomyces lipmanii and the oxalatedegrading bacterium Pseudomonas oxalaticus and anaerobes have not been enumerated from
the worm gut but several nitrogen fixers (Clostridium butyricum, Clostridium beijerinkii and
Clostridium paraputrificum) have been isolated from Eisenia foetida casts, microbial growth
was limited by the amount of available carbon immobilization of phosphate in earthworm
casts is probably caused by mainly abiotic processes, carbon mineralization by soil
microflora fertilizer with glucose and phosphorous was limited by nitrogen, except in freshly
deposited casts [12]
Mathur [10] states that it gut of earthworm behaved as an epigenic/anecic species in
sugarcane fields in Australia, where it seems to feed on decayed sugarcane liter and deposits
its casts on the soil surface. Karsten [12] reported that the digestive enzymes and intestinal
microflora of earthworms seem to play an important role in digestive of soil organic matter,
the various enzymes viz., amylase, cellulose, xylanase, cellbiose, endonuclease, acid
phosphatase and their activities in the gut of the two selected earthworms Eudrilus eugenie,
Eisenia foetids.
Yasir et al. [13] showed that changes in bacterial community play a major role during
vermicomposting. In addition to bacteria, fungi especially cellulolytic fungi also play an
important role during vermicomposting. Population of cellulolytic fungi was found to be
increased during vermicomposting of different organic wastes. Cellulase produced by these
fungi plays a major role in decomposition of cellulolytic materials of organic wastes.
Prabhat Pramanik and Young Ryun Chung [14] used two wastes as food for two epigeic
earthworms (Eisenia fetida and Eudrilus eugeniae) to standardize the recycling technique of
these two wastes and to study their effect on fungal especially cellulolytic fungal population,
cellulase activity and their isozyme pattern, chitin content and microbial biomass of waste
mixture during vermicomposting. Increasing VN proportion from 25% to 50% or even
higher, counts of both fungi and cellulolytic fungi in waste mixtures were significantly
increased during vermicomposting. Higher chitin content in vinasse-enriched treatments
suggested that fungal biomass and fungi-to-microbial biomass ratio in these treatments were
also increased due to vermicomposting.
EFFECT OF VERMICOMPOST MATERIALS IN AGRICULTURE
Vermicomposting is a process of biotransforming and stabilizing organic materials (often
waste) into humus by the combined activity of earthworms and microorganisms [15].
Earthworms excrete partially digested materials, known as vermicasts or castings, which are
more homogeneous in composition than the source material, have reduced levels of
contamination, and contain elevated levels of plant growth regulators or symbiotic microbes
and organic acids such as humic and fulvic acids [16]. Vermicomposting refers to production
of compost by growing/ breeding earthworms as these worms in the process of feeding on
waste cause biooxidation by relentless turning, fragmentation and aeration of waste by
devouring resulting in homogeneous and stabilized humus like product which is an ideal
nutrient for plants thus used as manure.
Vermicomposting of biodegradable Municipal Solid Waste and household waste is in vogue
in many places and instances but there is no available literature on use of vermicomposting
technique for treatment and disposal of infected biomedical waste. There is an emerging
commercial trend of aerobically incubating an extract of compost with a carbohydrate and a
protein source, producing a microbially enhanced liquid [17]. Known by the agricultural
sector as ‘compost teas’ in the current study this microbially enhanced product is termed
‘‘Compost Extract’’ or ‘‘CE’’ in short. Compost extract contains nutrients extracted from
compost and thus contributes directly to plant nutrition, and also contains organic matter,
improving soil structure and water holding capacity by building soil aggregates.
Composting and vermicomposting are quite distinct processes, particularly concerning the
optimum temperatures for each process and the types of microbial communities that
predominate during active processing (i.e. thermophilic bacteria in composting, mesophilic
bacteria and fungi in vermicomposting). The wastes processed by the two systems are also
quite different. Edwards et al. [18] reported that vermicomposts have a much finer structure
than composts and contain nutrients in forms that are readily available for plant uptake. There
have also been reports by Tomato and Galli [19] of production of plant growth regulators in
the vermicomposts. Therefore, they hypothesized that there should be considerable
differences in the performances and effects of composts and vermicomposts on plant growth
when used as soil amendments or as components of horticultural plant growth media.
Application of vermicomposting in combination with NPK fertilizers resulted in higher
content of total nitrogen compared to FYM in combination with NPK fertilizers or control. It
also resulted in higher content of phosphorus significantly [20]. The casting by earthworms
was seen to improve, the soil organic matter and nutrient status, by recycling available
nutrients especially N, P, K, Ca and Mg [23]. Application of coir dust coir pith into soil
contributes 20.7 kg N, 10.5 kg, P2O5 and 30.8 kg K2O ha annually. Coir pith being a rich
potash source also helps to retain moisture in the soil for a long time.
EFFECT OF VERMICOMPOST ON PHYSICO-CHEMICAL CHARACTERISTICS
OF SOIL
The composted organic wastes exert variety of physical, chemical and biochemical influences
upon the soil faking the soil a favourable substrate for plant growth. It maintains the soil in a
proper homeostaitc state. It also removes excessive amounts of heavy metals such as copper
and lead and there by served as a means of detroxification. Kumaresan et al. [21] reported
that there was a slight decrease of pH due to the organic acids released during the
decomposition of the various farm wastes. The EC value was also altered by the organic
waste application into the soil. There was a significant increase in the available N status due
to the application of the various farm waste materials. The available P status was also
significantly increased by the application of the various farm waste materials. The application
of organic wastes into soil has considerably increased the available K status also.
Application of vermicomposting in combination with NPK fertilizers resulted in higher
content of total nitrogen compared to FYM in combination with NPK fertilizers or control. It
also resulted in higher content of phosphorus significantly (Kale et al. [22]. The casting by
earthworms was seen to improve, the soil organic matter and nutrients status, by recycling
available nutrients especially N, P, K, Ca and Mg. Application of coir dust coir pith into soil
contributes 20.7 kg N, 10.5 kg, P2O5 and 30.8 kg K2O ha annually. Coir pith being a rich
potash source also helps to retain moisture in the soil for a long time.
Nutrient composition and physico-chemical parameters are subjected to greater changes due
to activity of earthworms in food substrates, while mineralization of waste substrates is
accelerated by passing of ingested food through gut of earthworms, thus stabilizing NPK
contents in plant available form. The nutrient contents and physico-chemical parameters of
vermicompost samples obtained in the present study looked optimum and are considerable to
such earthworm mediated compost [23].
Karuna Shrestha et al. [24] investigated the physico-chemical and microbiological
investigations on rumen content material composted for nine months, fresh vermicasts
(obtained after passing the same compost through the guts of a mixture of three species of
earthworms: Eisenia fetida, Lumbricus rubellus and Perionyx excavates) and microbially
enhanced extracts derived from rumen compost, vermicast and vermicast leachate incubated
for upto 48 hours. Compared to composted rumen contents, vermicast was only improved in
terms of microbial biomass C, while vermicast leached extract was significantly higher in
NH4 -N; PO4 -P, humic acid, bacterial counts and total microbial activity compared to rumen
compost extract.
The application of vermicompost increased the growth and yield of paddy besides increasing
the levels of total nitrogen, available phosphorous and potassium and micronutrients in the
soil. The fertilizing effect of earthworm casts depends on microbial metabolites, mainly
growth regulators. Earthworm casts promoted the root initiation and root biomass. The
chemical fertilizer application along with vermicompost increased the nutrients uptake and
the net production of wheat and sugarcane. Vermicompost is superior to normal compost in
increasing the growth of cardamom seedlings. Significant increase in the yield due to saw
dust was observed compared to nitrogenase fertilizers application alone. The general vigor of
the crop was more with profuse tillering under saw dust compost amendments while with
nitrogenous fertilizer alone spans or no tillering was observed [25].
Vermicompost contains plant growth regulators and other plant growth influencing materials
produced by microorganisms. Vermicompost a by-product of earthworm mediated organic
waste recycling is rich in plant nutrients and growth promoting substances. Having shown to
promote and sustain crop yields [26].
IMPORTANCE OF VERMICOMPOST
Source of plant nutrients
Earthworms consume various organic wastes and reduce the volume by 40–60%. Each
earthworm weighs about 0.5 to 0.6 g, eats waste equivalent to its body weight and produces
cast equivalent to about 50% of the waste it consumes in a day. These worm castings have
been analyzed for chemical and biological properties. The moisture content of castings ranges
between 32 and 66% and the pH is around 7.0. The worm castings contain higher percentage
(nearly twofold) of both macro and micronutrients than the garden compost.
From earlier studies also it is evident that vermicompost provides all nutrients in readily
available form and also enhances uptake of nutrients by plants. Sreenivas [27] studied the
integrated effect of application of fertilizer and vermicompost on soil available nitrogen (N)
and uptake of ridge gourd (Luffa acutangula) at Andhra Pradesh, India. Soil available N
increased significantly with increasing levels of vermicompost and highest N uptake was
obtained at 50% of the recommended fertilizer rate plus 10 t ha-1 vermicompost. Similarly,
the uptake of N, phosphorus (P), Potassium (K) and magnesium (Mg) by rice (Oryza sativa)
plant was highest when fertilizer was applied in combination with vermicompost.
Improvement of plant growth and yield
Vermicompost plays a major role in improving growth and yield of different field crops,
vegetables, and flower and fruit crops. The application of vermicompost gave higher
germination (93%) of mung bean (Vigna radiata) compared to the control (84%). Further, the
growth and yield of mung bean was also significantly higher with vermicompost application.
Likewise, in another pot experiment, the fresh and dry matter yields of cowpea (Vigna
unguiculata) were higher when soil was amended with vermicompost than with biodigested
slurry [28].
The efficiency of vermicompost was evaluated in a field study by Desai et al. [29]. They
stated that the application of vermicompost along with fertilizer N gave higher dry matter
(16.2 g plant-1) and grain yield (3.6 t ha-1) of wheat (Triticum aestivum) and higher dry matter
yield (0.66 g plant-1) of the following coriander (Coriandrum sativum) crop in sequential
cropping system. Similarly, a positive response was obtained with the application of
vermicompost to other field crops such as sorghum (Sorghum bicolor) and sunflower
(Helianthus annuus).
Application of vermicompost at 5 t ha-1 significantly increased yield of tomato (Lycopersicon
esculentum) (5.8 t ha-1) in farmers fields in Adarsha watershed, Kothapally, Andhra Pradesh
compared to control (3.5 t ha-1). Similarly, greenhouse studies at Ohio State University in
Columbus, Ohio, USA have indicated that vermicompost enhances transplant growth rate of
vegetables. Amendment of vermicompost with a transplant grown without vermicompost had
the highest amount of red marketable fruit at harvest. In addition, there were no symptoms of
early blight lesions on the fruit at harvest. The yield of pea (Pisum sativum) was also higher
with the application of vermicompost (10 t ha-1) along with recommended N, P and K than
with these fertilizers alone.
Vadiraj et al. [30] reported that the application of vermicompost produced herbage yields of
coriander cultivars that were comparable to those obtained with chemical fertilizers. The
fresh weight of flowers such as Chrysanthemum chinensis increased with the application of
different levels of vermicompost. Also, the number of flowers per plant (26), flower diameter
(6 cm) and yield (0.5 t ha-1) were maximum with the application of 10 t ha-1 of vermicompost
along with 50% of recommended dose of NPK fertilizer. However, the vase life of flowers
(11 days) was high with the combined application of vermicompost at 15 t ha-1 and 50% of
recommended dose of NPK fertilizer.
Reduction in soil C:N ratio
Vermicomposting converts household waste into compost within 30 days, reduces the C:N
ratio and retains more N than the traditional methods of preparing composts [31]. The C:N
ratio of the unprocessed olive cake, vermicomposted olive cake and manure were 42, 29 and
11, respectively. Both the unprocessed olive cake and vermicomposted olive cake
immobilized soil N throughout the study duration of 91 days. Cattle manure mineralized an
appreciable amount of N during the study. The prolonged immobilization of soil N by the
vermicomposted olive cake was attributed to the C:N ratio of 29 and to the recalcitrant nature
of its C and N composition. The results suggest that for use of vermicomposted dry olive
cake as an organic soil amendment, the management of vermicomposting process should be
so adjusted as to ensure more favorable N mineralization and immobilization.
Role in Nitrogen cycle
Earthworms play an important role in the recycling of N in different agro-ecosystems,
especially under jhum (shifting cultivation) where the use of agrochemicals is minimal.
Karmegam and Daniel [32] reported that during the fallow period intervening between two
crops at the same site in 5- to 15-year jhum system, earthworms participated in N cycle
through cast-egestion, mucus production and dead tissue decomposition. Soil N losses were
more pronounced over a period of 15-year jhum system. The total soil N made available for
plant uptake was higher than the total input of N to the soil through the addition of slashed
vegetation, inorganic and organic manure, recycled crop residues and weeds.
Improvement of soil physical, chemical and biological properties.
Limited studies on vermicompost indicate that it increases macropore space ranging from 50
to 500 m, resulting in improved air-water relationship in the soil which favorably affects
plant growth [33]. The application of organic matter including vermicompost favorably
affects soil pH, microbial population and soil enzyme activities. It also reduces the proportion
of water-soluble chemical species, which cause possible environmental contamination.
CONCLUSION
In recent years, the ecological characteristics and beneficial effects of earthworm have
been clearly demonstrated, focused by scientific research. Earthworm’s activity influences
the rate of soil turnover, mineralization and humification of soil organic matter. Improvement
in the consistency of soil texture with a concomitant increase in porosity, infiltration and soilwater retention are other characteristics of worm-worked soils. There are multiple benefits of
vermitechnology; low cost production of biofertilizer, environmental management of solid
wastes and agricultural residues, enhanced soil productivity, tastier quality food, among
others. Vermitechnology also aids in the reduction of soil salinity, soil erosion with less
runoff and wasteland development. From this present review, it is concluded that the organic
wastes are effectively recycled by microorganisms followed by earthworms and plays a major
role in the development of growth and yield of agricultural crops. The nutritive value of
compost material is high and the composting process effectively converts the waste product
into useful by-product.
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