Vermicomposting and
maturity indices of composting
1. Introduction
Earthworms
have been on the Earth for over 20 million years. In this time they have
faithfully done their part to keep the cycle of life continuously moving. Their
purpose is simple but very important. They are nature’s way of recycling
organic nutrients from dead tissues back to living organisms. Many have
recognized the value of these worms. Ancient civilizations, including Greece
and Egypt valued the role earthworms played in soil. 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. Charles Darwin was intrigued by the worms and studied them for 39 years.
Referring to an earthworm, Darwin said, “It may be doubted whether there are
many other animals in the world which have played so important a part in the
history of the world.” The earthworm is a natural resource of fertility and
life.
Earthworms
live in the soil and feed on decaying organic material. After digestion, the
undigested material moves through the alimentary canal of the earthworm, a thin
layer of oil is deposited on the castings. This layer erodes over a period of 2
months. So although the plant nutrients are immediately available, they are
slowly released to last longer. The process in the alimentary canal of the
earthworm transforms organic waste to natural fertilizer. The chemical
changes that organic wastes undergo include deodorizing and neutralizing. This
means that the pH of the castings is 7 (neutral) and the castings are odorless.
The worm castings also contain bacteria, so the process is continued in the
soil, and microbiological activity is promoted.
Vermicomposting is the
process of turning organic debris into worm castings. The worm castings are
very important to the fertility of the soil. The castings contain high amounts
of nitrogen, potassium, phosphorus, calcium, and magnesium. Castings contain: 5
times the available nitrogen, 7 times the available potash, and 1 ½ times more
calcium than found in good topsoil. Several researchers have demonstrated that
earthworm castings have excellent aeration, porosity, structure, drainage, and
moisture-holding capacity. The content of the earthworm castings, along with
the natural tillage by the worms burrowing action, enhances the permeability of
water in the soil. Worm castings can hold close to nine times their
weight in water. “Vermiconversion,” or using earthworms to convert waste into soil
additives, has been done on a relatively small scale for some time. A
recommended rate of vermicompost application is 15-20 percent.
Vermicomposting
is done on small and large scales. In the 1996 Summer Olympics in Sydney,
Australia, the Australians used worms to take care of their tons and tons of
waste.They then found that waste produced by the worms was could be very
beneficial to their plants and soil. People in the U.S. have commercial
vermicomposting facilities, where they raise worms and sell the castings that
the worms produce. Then there are just people who own farms or even small
gardens, and they may put earthworms into their compost heap, and then use that
for fertilizer.
Vermicompost and its utilization
Vermicompost is nothing but the excreta of earthworms, which is rich in humus
and nutrients. We can rear earthworms artificially in a brick tank or near the
stem / trunk of trees (specially horticultural trees). By feeding these
earthworms with biomass and watching properly the food (bio-mass) of
earthworms, we can produce the required quantities of vermicompost.
2. Materials for preparation of Vermicompost
Any types of
biodegradable wastes-
- Crop residues
- Weed biomass
- Vegetable waste
- Leaf litter
- Hotel refuse
- Waste from agro-industries
- Biodegradable portion of urban and rural wastes
Phase of vermicomposting
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Phase 1
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Processing involving
collection of wastes, shredding, mechanical separation of the metal, glass
and ceramics and storage of organic wastes.
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Phase 2
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Pre digestion of
organic waste for twenty days by heaping the material along with cattle dung
slurry. This process partially digests the material and fit for
earthworm consumption. Cattle dung and biogas slurry may be used after
drying. Wet dung should not be used for vermicompost production.
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Phase 3
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Preparation of
earthworm bed. A concrete base is required to put the waste for vermicompost
preparation. Loose soil will allow the worms to go into soil and also
while watering, all the dissolvable nutrients go into the soil along with
water.
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Phase 4
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Collection of
earthworm after vermicompost collection. Sieving the composted material
to separate fully composted material. The partially composted material
will be again put into vermicompost bed.
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Phase 5
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Storing the
vermicompost in proper place to maintain moisture and allow the beneficial
microorganisms to grow.
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What Worms Need
The Five Essentials
Compost worms need five basic things:
- An hospitable living environment, usually called
“bedding”
- A food source
- Adequate moisture (greater than 50% water content by
weight)
- Adequate aeration
- Protection from temperature extremes
These five essentials
are discussed in more detail below.
Bedding
Bedding is any material
that provides the worms with a relatively stable habitat. This habitat must
have the following characteristics:
High absorbency
Worms breathe through
their skins and therefore must have a moist environment in which to live. If a
worm’s skin dries out, it dies. The bedding must be able to absorb and retain
water fairly well if the worms are to thrive.
Good bulking potential
If the material is too
dense to begin with, or packs too tightly, then the flow of air is reduced or
eliminated. Worms require oxygen to live, just as we do. Different materials
affect the overall porosity of the bedding through a variety of factors,
including the range of particle size and shape, the texture, and the strength
and rigidity of its structure. The overall effect is referred to in this
document as the material’s bulking potential.
Low protein and/or nitrogen content (high Carbon: Nitrogen ratio)
Although the worms do
consume their bedding as it breaks down, it is very important that this be a
slow process. High protein/nitrogen levels can result in rapid degradation and
its associated heating, creating inhospitable, often fatal, conditions. Heating
can occur safely in the food layers of the vermiculture or vermicomposting
system, but not in the bedding.
Requirements
- Housing: Sheltered culturing of worms is recommended to protect
the worms from excessive sunlight and rain. All the entrepreneurs have set
up their units in vacant cowsheds, poultry sheds, basements and back
yards.
- Containers: Cement tanks were constructed. These were separated in
half by a dividing wall. Another set of tanks were also constructed for
preliminary decomposition.
- Bedding and feeding materials: During the beginning of the enterprises, most women
used cowdung in order to breed sufficient numbers of earthworms. Once they
have large populations, they can start using all kinds of organic waste.
Half of the entrepreneurs have now reached populations of 12,000 to 15,000
adult earthworms.
3. Vermicompost Production Methodology
i) Selection of suitable earthworm
For vermicompost
production, the surface dwelling earthworm alone should be used. The earthworm,
which lives below the soil, is not suitable for vermicompost production.
The African earthworm (Eudrillus engenial), Red worms (Eisenia foetida) and composting worm (Peronyx excavatus) are promising worms used for vermicompost
production. All the three worms can be mixed together for vermicompost
production. The African worm (Eudrillus eugenial) is preferred over other two types, because it
produces higher production of vermicompost in short period of time and more
young ones in the composting period.
ii) Selection of site for
vermicompost production
Vermicompost
can be produced in any place with shade, high humidity and cool. Abandoned
cattle shed or poultry shed or unused buildings can be used. If it is to
be produced in open area, shady place is selected. A thatched roof may be
provided to protect the process from direct sunlight and rain. The waste heaped
for vermicompost production should be covered with moist gunny bags.
iii) Containers for vermicompost production
A
cement tub may be constructed to a height of 2½ feet and a breadth of 3 feet.
The length may be fixed to any level depending upon the size of the room.
The bottom of the tub is made to slope like structure to drain the excess water
from vermicompost unit. A small sump is necessary to collect the drain water.
In
another option over the hand floor, hollow blocks / bricks may be arranged in
compartment to a height of one feet, breadth of 3 feet and length to a desired
level to have quick harvest. In this method, moisture assessment will be very
easy. No excess water will be drained. Vermicompost can also be prepared
in wooden boxes, plastic buckets or in any containers with a drain hole at the
bottom.
iv) Vermiculture bed
Vermiculture
bed or worm bed (3 cm) can be prepared by placing after saw dust or husk or
coir waste or sugarcane trash in the bottom of tub / container. A layer of fine
sand (3 cm) should be spread over the culture bed followed by a layer of garden
soil (3 cm). All layers must be moistened with water. If available,
shredded paper or cardboard makes an excellent bedding, particularly when
combined with typical on-farm organic resources such as straw and hay. Organic
producers, however, must be careful to ensure that such materials are not
restricted under their organic certification standards. Paper or cardboard
fibre collected in municipal waste programs cannot be approved for
certification purposes. There may be cases, however, where fibre resources from
specific generators could be sourced and approved. This must be considered on a
case-by-case basis. Another material in this category is paper-mill sludge,
which has the high absorbency and small particle size that so well complements
the high C:N ratios and good bulking properties of straw, bark, shipped brush
or wood shavings. Again, the sludge must be approved if the user has organic
certification.
In
general, it should be noted by the reader that the selection of bedding
materials is a key to successful vermiculture or vermicomposting. Worms can be
enormously productive (and reproductive) if conditions are good; however, their
efficiency drops off rapidly when their basic needs are not met (see discussion
on moisture below). Good bedding mixtures are an essential element in meeting
those needs. They provide protection from extremes in temperature, the
necessary levels and consistency of moisture, and an adequate supply of oxygen.
Fortunately, given their critical importance to the process, good bedding
mixtures are generally not hard to come by on farms. The most difficult
criterion to meet adequately is usually absorption, as most straws and even hay
are not good at holding moisture. This can be easily addressed by mixing some
aged or composted cattle or sheep manure with the straw. The result is somewhat
similar in its bedding characteristics to aged horse manure.
Mixing
beddings need not be an onerous process; it can be done by hand with a
pitchfork (small operations), with a tractor bucket (larger operations), or, if
one is available, with an agricultural feed mixer. Please note that the latter
would only be appropriate for large commercial vermicomposting operations where
high efficiency levels and consistent product quality is required.
v) Worm Food
Compost
worms are big eaters. Under ideal conditions, they are able to consume in
excess of their body weight each day, although the general rule-of-thumb is ½
of their body weight per day. They will eat almost anything organic (that is,
of plant or animal origin), but they definitely prefer some foods to others.
Manures are the most commonly used worm feedstock, with dairy and beef manures
generally considered the best natural food for Eisenia, with the possible
exception of rabbit manure. The former, being more often available in large
quantities, is the feed most often used.
vi) Selection for vermicompost production
Cattle
dung (except pig, poultry and goat), farm wastes, crop residues, vegetable
market waste, flower market waste, agro industrial waste, fruit market waste
and all other bio degradable waste are suitable for vermicompost
production. The cattle dung should be dried in open sunlight before used
for vermicompost production. All other waste should be predigested with
cow dung for twenty days before put into vermibed for composting.
vii) Putting the waste in the container
The
predigested waste material should be mud with 30% cattle dung either by weight
or volume. The mixed waste is placed into the tub / container upto brim. The
moisture level should be maintained at 60%. Over this material, the selected
earthworm is placed uniformly. For one-meter length, one-meter breadth and
0.5-meter height, 1 kg of worm (1000 Nos.) is required. There is no necessity
that earthworm should be put inside the waste. Earthworm will move inside on
its own.
viii) Watering the vermibed
Daily
watering is not required for vermibed. But 60% moisture should be maintained
throughout the period. If necessity arises, water should be sprinkled
over the bed rather than pouring the water. Watering should be stopped before
the harvest of vermicompost.
ix) Harvesting vermicompost
In the
tub method of composting, the castings formed on the top layer are collected
periodically. The collection may be carried out once in a week. With hand
the casting will be scooped out and put in a shady place as heap like
structure. The harvesting of casting should be limited up to earthworm
presence on top layer. This periodical harvesting is necessary for free
flow and retain the compost quality. Other wise the finished compost get
compacted when watering is done. In small bed type of vermicomposting method,
periodical harvesting is not required. Since the height of the waste
material heaped is around 1 foot, the produced vermicompost will be harvested
after the process is over.
x) Harvesting earthworm
After
the vermicompost production, the earthworm present in the tub / small bed may
be harvested by trapping method. In the vermibed, before harvesting the
compost, small, fresh cow dung ball is made and inserted inside the bed in five
or six places. After 24 hours, the cow dung ball is removed. All the worms will
be adhered into the ball. Putting the cow dung ball in a bucket of water
will separate this adhered worm. The collected worms will be used for
next batch of composting.
Worm
harvesting is usually carried out in order to sell the worms, rather than to
start new worm beds. Expanding the operation (new beds) can be accomplished by
splitting the beds that is, removing a portion of the bed to start a new one
and replacing the material with new bedding and feed. When worms are sold,
however, they are usually separated, weighed, and then transported in a
relatively sterile medium, such as peat moss. To accomplish this, the worms
must first be separated from the bedding and vermicompost. There are three
basic categories of methods used by growers to harvest worms: manual,
migration, and mechanical. Each of these is described in more detail in the
sections that follow.
a) Manual Methods
Manual
methods are the ones used by hobbyists and smaller-scale growers, particularly
those who sell worms to the home-vermicomposting or bait market. In essence,
manual harvesting involves hand-sorting, or picking the worms directly from the
compost by hand. This process can be facilitated by taking advantage of the
fact that worms avoid light. If material containing worms is dumped in a pile
on a flat surface with a light above, the worms will quickly dive below the
surface. The harvester can then remove a layer of compost, stopping when worms
become visible again. This process is repeated several times until there is
nothing left on the table except a huddled mass of worms under a thin covering
of compost. These worms can then be quickly scooped into a container, weighed,
and prepared for delivery.
There are
several minor variations and/or enhancements on this method, such as using a
container instead of a flat surface, or making several piles at once, so that
the person harvesting can move from one to another, returning to the first one
in time to remove the next layer of compost. They are all labour-intensive,
however, and only make sense if the operation is small and the value of the
worms is high.
b) Self-Harvesting (Migration) Methods
These
methods, like some of the methods used in vermicomposting, are based on the
worms tendency to migrate to new regions, either to find new food or to avoid
undesirable conditions, such as dryness or light. Unlike the manual methods
described above, however, they often make use of simple mechanisms, such as
screens or onion bags.
The
screen method is very common and easy to use. A box is constructed with a
screen bottom. The mesh is usually ¼”, although 1/8” can be used as wel. There
are two different approaches. The downward-migration system is similar to the
manual system, in that the worms are forced downward by strong light. The
difference with the screen system is that the worms go down through the screen
into a prepared, pre-weighed container of moist peat moss. Once the worms have
all gone through, the compost in the box is removed and a new batch of worm-rich
compost is put in. The process is repeated until the box with the peat moss has
reached the desired weight. Like the manual method, this system can be set up
in a number of locations at once, so that the worm harvester can move from one
box to the next, with no time wasted waiting for the worms to migrate.
The
upward-migration system is similar, except that the box with the mesh bottom is
placed directly on the worm bed. It has been filled with a few centimeters of
damp peat moss and then sprinkled with a food attractive to worms, such as
chicken mash, coffee grounds, or fresh cattle manure. The box is removed and
weighed after visual inspection indicates that sufficient worms have moved up
into the material. This system is used extensively in Cuba, with the difference
that large onion bags are used instead of boxes. The advantage of this system
is that the worm beds are not disturbed. The main disadvantage is that the
harvested worms are in material that contains a fair amount of unprocessed
food, making the material messier and opening up the possibility of heating
inside the package if the worms are shipped. The latter problem can be avoided
by removing any obvious food and allowing a bit of time for the worms to
consume what is left before packaging.
xi) Nutritive value of vermicompost
The
nutrients content in vermicompost vary depending on the waste materials that is
being used for compost preparation. If the waste materials are heterogeneous
one, there will be wide range of nutrients available in the compost. If the
waste materials are homogenous one, there will be only certain nutrients are
available. The common available nutrients in vermicompost is as follows
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Organic carbon
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9.5 – 17.98%
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Nitrogen
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0.5 – 1.50%
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Phosphorous
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0.1 – 0.30%
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Potassium
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0.15 – 0.56%
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Sodium
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0.06 – 0.30%
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Calcium and Magnesium
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22.67 to 47.60
meq/100g
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Copper
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2 – 9.50 mg
kg-1
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Iron
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2 – 9.30 mg kg-1
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Zinc
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5.70 – 11.50 mg kg-1
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Sulphur
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128 – 548 mg kg-1
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xii) Storing and packing
of vermicompost
The harvested vermicompost should be stored in
dark, cool place. It should have minimum 40% moisture. Sunlight should not fall
over the composted material. It will lead to loss of moisture and
nutrient content. It is advocated that the harvested composted material is
openly stored rather than packed in over sac. Packing can be done at the time
of selling. If it is stored in open place, periodical sprinkling of water may
be done to maintain moisture level and also to maintain beneficial microbial
population. If the necessity comes to store the material, laminated over sac is
used for packing. This will minimize the moisture evaporation loss.
Vermicompost can be stored for one year without loss of its quality, if the
moisture is maintained at 40% level.
4. Advantages of vermicompost
- Vermicompost is rich in all essential plant nutrients.
- Provides excellent effect on overall plant growth,
encourages the growth of new
- shoots / leaves and improves the quality and shelf life
of the produce.
- Vermicompost is free flowing, easy to apply, handle and
store and does not have bad
- odour.
- It improves soil structure, texture, aeration, and
waterholding capacity and prevents
- soil erosion.
- Vermicompost is rich in beneficial micro flora such as
a fixers, P- solubilizers,
- cellulose decomposing micro-flora etc in addition to
improve soil environment.
- Vermicompost contains earthworm cocoons and increases
the population and
- activity of earthworm in the soil.
- It neutralizes the soil protection.
- It prevents nutrient losses and increases the use
efficiency of chemical fertilizers.
- Vermicompost is free from pathogens, toxic elements,
weed seeds etc.
- Vermicompost minimizes the incidence of pest and
diseases.
- It enhances the decomposition of organic matter in
soil.
- It contains valuable vitamins, enzymes and hormones
like auxins, gibberellins etc.
5. Pests and Diseases of vermicompost
Compost
worms are not subject to diseases caused by micro-organisms, but they are
subject to predation by certain animals and insects (red mites are the worst)
and to a disease known as “sour crop” caused by environmental conditions.
Maturity indices of
composting
Immature
and poorly stabilized composts may pose a number of problems during storage,
marketing and use. During storage these materials may develop anaerobic
‘pockets’ which can lead to odors, fire, and/or the development of toxic
compounds. Continued active decomposition when these materials are added to
soil or growth media may have negative impacts on plant growth due to reduced
oxygen and/or available nitrogen or the presence of phytotoxic compounds.
Compost maturity and stability are often used interchangeably. However, they
each refer to specific properties of these materials. There have been and will
continue to be efforts to develop and refine methods which evaluate stability
and maturity, but no one universally accepted and applied method exists.
Stability refers to a specific stage or decomposition or state of organic
matter during composting, which is related to the type of organic compounds remaining
and the resultant biological activity in the material. The stability of a given
compost is important in determining the potential impact of the material on
nitrogen availability in soil or growth media and maintaining consistent volume
and porosity in container growth media. Most uses of compost require a stable
to very stable product that will prevent nutrient tie up and maintain or
enhance oxygen availability in soil or growth media. Maturity is the degree or
level of completeness of composting. Maturity is not described by a single
property and therefore maturity is best assessed by measuring two or more
parameters of compost. Maturity is in part, affected by the relative stability
of the material but also describes the impact of other compost chemical
properties on plant development. Some immature composts may contain high
amounts of free ammonia, certain organic acids or other water-soluble compounds
which can limit seed germination and root development. All uses of compost
require a mature product free of these potentially phytotoxic components.
Appropriate laboratory tests must be easy, rapid and reliable for evaluation of
composts produced from all types of wastes with many different process methods.
Many methods have been proposed and are practiced to describe stability and
maturity. These include the carbon:nitrogen ratio (C:N); ammonium-N:nitrate-N
ratio; paper chromatography; humic substances analysis; microbial biomass;
cation exchange capacity (CEC); water extract analysis and; reheating tests.
All of these approaches can provide additional information on material
characteristics but have limitations when applied to the interpretation of the
diversity of compost products. As example, an assumed ideal C:N ratio for a
mature compost may be 10. However, certain raw and unstable waste materials
(e.g. some manures) may have low C:N ratiosCarbon/nitrogen ratio (C:N) less
than or equal to 25.
