1Division of Microbiology, Indian Agricultural Research Institute, India
2Division of Agricultural Engineering, Indian Agricultural Research Institute, India
3Division of Plant Pathology, Indian Agricultural Research Institute, India
Submission: June 02, 2016; Published: June 16, 2016
*Corresponding author: Livleen Shukla, Principal Scientist, Department of Microbiology, Indian Agricultural Research Institute (IARI), New Delhi-110012, India, Email:email@example.com
How to cite this article: Livleen S, Satish D L, Indra M M, Archna S, Annapurna K. Rural Composting for Improvement of Soil Health and Sustainable Agriculture. Agri Res & Tech: Open Access J. 2016; 1(5): 555572. DOI: 10.19080/ARTOAJ.2016.01.555572
Rural composting means a biochemical process in which diverse and mixed groups of micro-organisms breakdown organic materials to a humus-like substance which is similar in properties to farmyard manure. Rural compost has a lower bulk volume than the original raw organic material, is stable in nature, has a slow decomposition rate and can be returned to the soil without destruction of its high energy value. The process of composting poses neither hazard to human health nor to the environment, it is therefore, a desirable method of recycling rural organic residues. In other words, composting is the process by which organic materials are transformed into soil building substances for the farm, orchard or garden.
The broad objectives of rural composting are conserving and recycling farm residue resources, safeguarding rural public health and maintaining or improving the quality of the environment, all at a low cost and involving microbiological processes. There are several reasons for using compost but its main contribution is as a supplier of humus substances to soil, thus supplementing major plant nutrients (NPK) and being a good source for providing micronutrients whose deficiencies are showing up with intensive cropping and high productivity targets Sidhu et al. . An appropriate rural compost technology will make the recycling of farm wastes feasible and will minimize the pollution of water and land resources. The farmer has to recognize the need to maintain the marginal organic content of his soil by following a mixed agriculture system leading to resources moving from soil to crops, from crops to animals or back to soil and finally from animals to land Sidhu & Beri .
Organic materials: Rural compost is prepared from organic residues such as crop residues ( straw, leaves, rice husk, groundnut shell, sugarcane trash and bagasse), water hyacinth and other weeds, cattle dung, cattle urine and other animal wastes, the organic substance undergo intensive decomposition under thermophilic and mesophilic conditions in heaps or pits with adequate moisture and finally yield a dark colored humified material in three to six months which is more stable in form, valuable for replenishment of plant nutrients, maintenance of soil organic matter and in improving and maintenance of soil fertility. Alexander M .
The most important factors in the composting of rural residues are carbon-nitrogen ratios, shredding of material, blending of material, moisture, aeration, temperature, reaction, microorganisms involved, use of inoculants, amendments and destruction of pathogenic organisms.
Carbon/Nitrogen ratio: The carbon-nitrogen ratio of the organic materials is the most important factor in composting. The transformation of rural organic residues into manure is predominantly a microbiological process and so is influenced by the proportions of carbonaceous and nitrogenous materials present in the residues to be composted. Microorganisms need carbon for growth and nitrogen for protein synthesis. A C/N ratio of 30 to 40 is optimal for efficient composting and ratios between 25 and 40 have been found satisfactory. If the organic material is poor in Nitrogen i.e. if C/N ratio is wide, biological activity
decreases and several successions or cycles of microbial activities
would be required to accomplish degradation of the carbonaceous
material. Immobilized nitrogen is recycled on the death of some
of the organisms and the limited nitrogen is thus recycled for
reducing the carbon content of the residues. The completion of the
process is therefore delayed and finished compost takes longer to
produce. Chanyasak & Kubota . High C/N ratios are generally
caused by organic materials poor in nitrogen such as straw of
cereals, sugarcane trash, maize stalks, cotton stalks, jute stems and
sawdust. Rural residues have been found to vary widely in C/N
ratio-from 30 to 300. As the available nitrogen is exhausted, under
favorable C/N conditions the activity of nitrogen-fixing organisms
predominates and there is a gain of nitrogen from the atmosphere.
With a C/N ratio of raw materials less than 30:1, the proportion of
nitrogen is in excess of the requirements of the microorganisms.
In such cases although the process of decomposition goes on,
the unassailable nitrogen is lost by volatilization as ammonia or
by denitrification. At low C/N ratio, ammonia is formed under
favorable conditions and can be further oxidized to nitrite and
nitrate but low C/N ratio under unfavorable conditions causes loss
About 20 to 40% of nitrogen may be lost as ammonia during
preparation of compost from animal dung and water hyacinth.
This implies that a thorough mixing of these fractions with the
carbonaceous material of residues cannot be attained in practice
and there are always pockets of concentration of nitrogenous
material which causes an imbalance in the decomposition process
with loss of nitrogen. It has been seen that simple nitrogenous
compounds are more susceptible to loss and control of this loss
with a greater retention of nitrogen in the final compost is of
practical value in obtaining better quality compost. Beri et al.
. The time of composting high C/N residues can be reduced
by adding a nitrogen source or by blending with organic residues
richer in nitrogen like legume residues, grass cuttings, aquatic
weeds, green leaves.
Shredding of materials: The process of composting can
be accelerated if raw materials are shredded into small pieces
since it then becomes more susceptible to bacterial action due
to greater surface area exposure. The most desirable particle
size for composting is less than 5cm although larger sizes can be
composted satisfactorily. However, the advantage of shredding
on farms or by individuals is doubtful when one considers the
additional cost involved. Ajay K & Jawaid SM .
Blending of materials: The C/N ratio and moisture
percentage are two important parameters to be considered when
mixing together different kinds of material for composting. There
may not be any need of blending if the C/N ratio of the materials
is between 25 and 50, although a desirable range is 30 to 40.
Substances poor in nitrogen such as sawdust, straw, paper can be
mixed with comparatively nitrogen-rich materials such as biogas
slurry, leguminous plants, and so on to obtain a near optimum
ratio of 30 to 40. Similarly, wet and dry materials can be mixed together to obtain a desirable proportion of moisture and to avoid
anaerobic conditions. Soil at the rate of 5 to 10% can be added
to moist materials to reduce the moisture content and to absorb
ammonia while composting materials of low C/N ratio. Dry soil
may be added if sufficient dry organic materials are not available.
Soil may also be added to high C/N ratio organic material to buffer
acid conditions and to act as a diluents (for retarding anaerobic
processes). It can also be used for improving the appearance of the
finished compost by giving it a more granular structure.
Moisture and aeration: Moisture content and degree of
aeration are important factors in composting. If the amount
of moisture in the compost pile is below forty percent (W/W),
decomposition will be aerobic but slow. Aerobic decomposition
will occur at any moisture content between 30 and 100% if
adequate turning is provided but higher moisture contents should
be avoided. The optimum moisture level for aerobic composting
is 50-60% however; a range of 40-80% is quite satisfactory
depending upon the nature of the material to be composted. In
case of anaerobic composting, moisture level is not important.
Experiments with straw (a fibrous material) have resulted for the
maintenance of 80-85% moisture content Das K & Keener HM .
As the microorganisms multiply in the composting mass, the
heat of exothermic biochemical reactions is retained due to the
larger mass, when the temperature rises above 40ᵒC the mesophilic
microorganisms are replaced by thermophilic organisms. High
temperature is essential for destruction of pathogenic organisms
and weed seeds. This generally occurs within 2 to 7 days of the
start of operations. The temperature in the middle of the pile
goes up to 55-70ᵒC after which it gradually cools to ambient
values. Decomposition is fastest in the thermophilic range. The
optimum temperature for organic matter decomposition into
carbon dioxide and water has been found to be 600C and although
higher temperature is desirable but it should not exceed 71ᵒC for
long as decomposition will be slowed due to the thermal kill of
microorganisms. Only a few thermophilic organisms actively carry
on decomposition above 70ᵒC.
The initial pH value in compost heaps is generally slightly acidic
to neutral, around [6,7]. Lime may be applied for counteracting
acidity but nitrogen can be conserved without using limestone. It
has been seen that when calcium carbonate is added to compost
significant losses of nitrogen occur as the alkaline conditions
favors volatilization of ammonia.
Microorganisms involved: The microbial population
fluctuates during aerobic composting. There is a typical patternthe
fungi and acid producing bacteria appear during the mesophilic
stage. As the temperature increases above 40ᵒC these organisms
are replaced by thermophilic bacteria, actinomycetes and fungi.
Spore-forming bacteria develop at still higher temperatures and
finally, mesophilic bacteria and fungi reappear as the temperature again falls. The role of mesophilic bacteria involved in the
raising of temperature of the compost for the development of
the thermophilic bacteria which colonies the mass. Mesophilic
bacteria, which flourish during a limited time, consume most
of the readily degradable carbohydrates and proteins. Bacillus
sp. is especially involved in degradation of proteins, aminoacids,
peptones. Actinomycetes degrade starch very actively
and also bring about large losses of water soluble fractions.
Thermophilic bacteria attack lipids and hemicelluloses. Lipids
are degraded to great extent whereas degradation of celluloses
and hemicelluloses is comparatively slow and intermediate.
Lignin is most resistant compounds to decomposition. Division of
Microbiology has developed a consortium of four fungi Aspergillus
awamori, Aspergillus nidulans, Phaenerochaete chrysosporium
and Trichoderma viride for composting crop residues. Inoculants
are being sold at Rs. 30 per packet. A packet of 300g is enough to
decompose one tone of organic matter within 90 days. Singh et
Microbial inoculants: If the C/N ratio is too high adding
nitrogen can speed up the composting process by lowering the
ratio and thus leading to greater biodegradation. Addition of
microorganisms is also beneficial when compost heaps/pits are
poor in microbial content.
There are diverse types of raw materials available in rural
areas which can be utilized for preparation of compost. They can
be classified into five broad groups - Crop residues and weeds,
animal shed wastes, human wastes, kitchen wastes and forest
residues (Table 1).
The farm wastes and residues are scattered organic resources
and include readily available materials such as rice straw, wheat
straw, maize stalks, millet residues, banana, cotton, coconut,
red gram sticks and sugarcane trash. The leaves of cotton, jute,
cassava, coconut, papaya, tamarind, mango, guava and other crops
are available in different and specific seasons in large quantities.
The various kinds of farm weeds can be dried and composted
or the green weeds can be composted together with dry organic
materials from other sources. Water hyacinth is an aquatic weed
that grows luxuriantly in water and is often a nuisance, but the
plant can be harvested and composted into valuable manure.
Animal shed wastes are produced in large quantities in villages
and small towns and are either composted or burnt as fuel. These
materials are potential resources for blending with crops residues
when composting Hall J M & Sansoucy R .
Kitchen wastes and forest residues are equally important
groups of materials for rural composting. Kitchen wastes can
serve as a good blending material when composting dry and high
C/N ratio farm residues. Nitrogen content and carbon-nitrogen
ratio-one of the most critical factors in successful composting is
the nitrogen content and its ratio to carbon in the raw materials.
Therefore, these values should be known if possible and made
available to the farmer. In due course, a farmer will be able to
predict and identify the range of C/N ratio of organic masters
commonly available in rural areas for blending or proportioning
different types of raw materials for composting. As a general rule,
crop residues and particularly straw, stems, and so on, are wide
C/N ratio materials ranging from 50 to 120 whereas the green
succulent materials (green manure crops, leguminous residues),
animal shed wastes and vegetable and kitchen wastes are narrow
to medium C/N ratio materials generally ranging between 10 and
25. Sawdust and rice husk have very wide ratio between 130 and
500. Sawdust contains a high quantity of lignin and this coupled
with its high C/N ratio causes a very slow rate of decomposition.
However, sawdust has good urine and water holding properties
and can be used in composting at up to ten percent of the total
biomass of raw material (Table 2,3).
An important advance in the practice of composting was made
at Indore in India by Howard in collaboration with Jackson and
Wad during the period 1924 to 1926. The traditional procedure
was systematized into a method of composting now known as the
‘Indore method’. The materials needed are mixed plant residues,
animal dung and urine, earth, wood ash and water. All vegetable
wastes available on a farm such as weeds, stalks, stems, fallen
leaves, pruning, chaff, fodder remnants, green matter and so
on, are collected and stacked in a pile. Hard woody material like
cotton or Pigeon pea stalks and stubble are first spread on the
farm road and crushed under vehicles such as tractors or bullock
carts before being piled. Such hard materials should in any in any
case not exceed 10% of the total plant residues. Green materials
which are soft and succulent are allowed to wilt for 2 or 3 days to
remove excess moisture before being piled. Such hard materials
should in any case not exceed 10% of the total plant residues.
Green materials which are soft and succulent are allowed to wilt
for 2 or 3 days to remove excess moisture before stacking, they
tend to pack closely if they are stacked in the fresh state while
stacking, each material is spread in layers of about 15 centimeters
thickness until the heap is about one and a half meters high. The
mixture of different kinds of vegetable residues ensures a more
efficient decomposition Goluekem C . The heap is then cut into
vertical slices and about 20-25 kilogram is put under the feet of
cattle in the shed as bedding for the night. The next morning the
bedding, along with the dung and urine and urine-earth is taken to
the pit where the composting is to be done BSI .
Site and size of pit: The site selected for the compost pit
should be at high level so that no rain water gets in during the
monsoon season; it should be near to cattle and shed may be
constructed over it to protect the compost from heavy rainfall. The
pit should be about 1 m deep, 1.5 to 2.0 m wide and of any suitable
length. Open Pit Surface Mine Mine Engineer Community (2000)
accessed 19 December .
Filling pit: The material brought from the cattle shed is spread
and a slurry of dung made with 4.5 kg dung, 3.5 kg urine-earth
and 4.5 kg of inoculums taken from a fifteen days old composting
pit. A sufficient quantity of water/nearly 90% is sprinkled over
the material in the pit to wet it. The pit is filled in this way layer
by layer and it should not take longer than one week to fill. Care
should be taken to avoid compacting the material in any way.
During rainy season or in region with heavy rainfall the
compost may be prepared in heaps above ground and protected
by shed. When sufficient nitrogenous material is not available a
green manure or leguminous crop like sun hemp is grown on the
fermenting heap by sowing seeds after the first turning. The green
matter is then turned in at the time of the record mixing.
Dimensions: The basic Indore pile is about 2 m wide at the
base, 1.5 m high and 2 m long. The sides are tapered so that top
is about 0.5 m narrower in width than the base. A small bund is
sometimes built around the pile to protect it from wind which
tends to dry the heap.
Forming the heap: The heap is usually commenced with a
20 cm layer of carbonaceous material such as leaves, hay, straw,
sawdust, wood chips and chopped corn stalks. This is then covered
with 10 cm of nitrogenous material such as fresh grass, weed or
garden plant residues, garbage, fresh or dry manure or digested
sewage sludge. The pattern of 20 cm carbonaceous material and
10 cm nitrogenous material is followed until the pile is 1.5 m high
and they are normally wilted so that they feel damp but not soggy.
The pile is sometimes covered with soil or hay to retain heat and
is turned at six and twelve week intervals. If materials are limited,
the alternate layers can be added as they become available. Also,
all materials may be mixed together in the pile if one is careful to
maintain the proper proportions. Shredding the material speed up
decomposition considerably, most materials can be shredded by
running over it several times with a rotary mower.
Advantage and limitation: This method of composting is
recommended where land and labor are easily available. The
process can also be partially mechanized to make it economical
when large quantities of material are to be handled. The labor
requirements are relatively high but compost preparation can
help the unemployed in villages to earn a living. Preparation on a
large scale can be done through community composting. There is
lack of protection from rain and wind. A considerable amount of water is needed and so the method is not suitable in areas of scanty
rainfall. The intense aerobic decomposition to which material is
subjected no doubt shortens the period of composting but it leads
to heavy losses of organic matter and nitrogen. Therefore the C/N
ratio should be maintained about 30 to 40 to reduce such losses.
Large scale compost preparation by windrow method involves
the creation of windrows with a length of 40 m each consists of
mainly paddy straw and leaf litter in a ratio of (1:3) volume
basis. Each windrows consisting of paddy straw mix, cow dung,
good quality soil, old compost in the ratio of 8: 1: 0.5: 0.5. All the
biomass ingredients along with compost inoculants are mixed
thoroughly with 3-4 days’ old cow dung before forming windrow.
The compost mechanical loader is use for making windrows.
Windrows are kept in trapezoidal shape with a bottom width of 2
m and a top width of 1.5 m to match the width of the rotor of the
Turner-cum-Mixer. To enhance the process of composting, PUSA
Compost Inoculants developed at IARI is added at a rate of 1000
ml per tone of the material. In practice, 27 liters of culture is mixed
with 100 liters of water and sprayed on the top of the windrows
manually. The manual spraying is preferred as bigger fungal mats
creates problem while passing through the nozzle of the regular
Machines for windrow composting: A set of machines
namely Compost Turner-cum-Mixer, Automatic Compost Sieving
machine and a tractor front-mounted loader are useful for quality
compost making and handling. Compost Turner-cum-Mixer is a
trailing and offset type machine used for thoroughly mixing the
cow dung, farm residues and biomass for manure preparation. The
main components of the equipment are a mixing rotor, a hydraulic
system to operate the rotor, and a water tank to store water and
culture and the machine also has a side tank for weight balancing.
Blades arranged in a helical path on rotor in order to facilitate
thorough mixing and turning of the material. Rubber pads are
also provided for partially covering the mixing unit to check the
spillage of compost while mixing. Automatic Compost Sieving
Machine is suitable for sieving and separating the finer grade
material from the coarse grade one. Sieving machine is provided
with an automatic belt feeding mechanism, a compost separator
unit and hopper for safe feeding, and a belt conveyor based unit
for conveying the finished quality compost. Separation in different
sizes is done for value addition. A tractor front-mounted loader is
useful for the purpose of handling of materials i.e. loading, shifting
and shaping of the raw materials. The mechanization of the
windrow compost making process has provided the avenue for a
large scale production of good quality compost in a much rapid
manner without drudgery to laborers.
Advantage and limitation: Windrow method is economical
for large scale commercial compost preparation. Compost
preparation by manual method is labor intensive. Also, handling
cow dung manually is full of drudgery. The use of machines overcomes the labor problem and fastens the compost preparation
process while imparting dignity to labor. The technology facilitates
compost making in 45-60 days, whereas in traditional pit method
it takes almost 120-140 days depending upon the ingredients and
The method of composting was developed at Bangalore in
India by Acharya . The method is basically recommending
when night soil and refuse are used for preparing the compost. The
method over come many of a disadvantage of the Indore method
but the time involved in production of finished compost is much
longer. The method is suitable for areas with a scanty rainfall.
Preparation of the pit: Trenches or pits about one meter
deep are dug; the breadth and length of the trenches can be made
depending on the availability of land and the type of material to
be composted. The selection of site for the pits is made as in the
Indore method. The trenches should preferably have sloping walls
and a floor of 90 cm slope to prevent water logging.
Filling the pit: Organic residues and night soil or animal
dung are put in alternate layer and after filling. The pit is covered
with a 15 cm to 20 cm thick layer of refuse. The materials are
allowed to remain the pit without turning and watering for three
months. During the period material settles down due to reduction
in volume of the biomass and additional night soil and refuse in
alternate layer are placed on top and plastered or covered with
mud or earth to prevent loss of moisture and breeding of flies.
After the initial, aerobic composting which is for about eight to
ten days, the material undergoes anaerobic decomposition at a
very slow rate and it take about six to eight months to obtain the
Advantage and limitation: The recovery of the finished
product is much greater as compared to aerobic composting; loss
of nitrogen is negligible. Labor requirement is less than the Indore
method as turning of materials is not done; labor is needed only
for digging and filling the pits. The method requires a long time
to produce finished compost and so takes up more land use. A
uniform high temperature is not assured in the biomass. Problems
of odor and fly breeding need to be attended to.
The digging and preparation of a compost pit: The pits can
be partitioned into two with partitions made from hardy straw
materials. The sources are generally cattle dung mixed with straw
and stubble and used as bedding for the animals, different kinds
of farm weeds in addition to crops residues. The straw material,
rural garbage and so on are spread in the pit layer by layer and
rock phosphate or superphosphate added.
High temperature compost: This form of compost is
prepared mainly from night soil, urine, sewage, animal dung and
chopped residues at ratio 1:4. The material are heaped in alternate
layer starting with chopped plant stalk and followed by human and animal waste, water is added to optimum plant amount. At the
time of making the heap a number of bamboo poles are inserted
for aeration purposes. After the heap formation is complete, it is
sealed with 3 cm of mud plaster. The bamboo poles are withdrawn
after one day of composting clearing the holes for aeration of the
heap. Within four or five days the temperature rises to 60-70ᵒC
and the holes are then sealed with mud. The compost is ready for
use within two months and is considered free from pathogen.
This method of compost was developed at the University of
California at Berkley (1953). Compost can be prepared within two
week by the method.
Raw materials: For rapid decomposition a mixture of organic
residues in the proportion of two part of cellulose-rich material
to one part of nitrogen-rich materials should be used. However,
pure cellulose material such as paper waste should not form
more than ten percent of the raw material to be composted. It is
recommended that the leaves of all kinds, grass clipping and dry
manure should be mixed and shredded with a mechanical device
before the heaps are made. The C/N ratio of the mixed Berkley
organic wastes average 30:1.
Dimensions of the berkley composting heap and
procedure: The material is composted in heaps of 2.4 m by 2.2 m
with a height of about 1.5 m and it is composted for two weeks. By
the second or third day thermophilic temperature develops and
the heap should be turned with thorough mixing on the fourth
day. The turning and mixing is repeated on the seventh and tenth
days. At this stage the temperature normally starts to decrease
and within two weeks the compost is ready for use. The original
raw material will be somewhat recognizable but the appearance
should be coarse, crumbly and dark brown. If finer compost is
required it may be allowed to decompose further or it could be
sieved and stored.
Advantages and limitation: The main advantages of the
Berkley method is speed since large quantities of compost can be
prepared in a relatively short time. The turning schedule is tight
and labor intensive. There is a limitation of using material with a
narrow C/N ratio.
Composted organic material that is applied to agricultural
land should be sufficiently decomposed and should not have a
detrimental effect on the growth of plant. The finished compost is
designated by the general name humus. Humus may be described
as a complex aggregate, dark brown to black in color of amorphous
colloidal substances resulting from the microbiological
breakdown of plant and animal residues under aerobic or
anaerobic condition chemically, humus is heterogeneous material
composed of different type of polymerized substances such as
aromatic molecule. Polysaccharides of several kinds, bound
amino-acids, polymer of uronic acids and phosphorus-containing substance synthesized by microorganisms, complex resulting
from decomposition, substances still undergoing decomposition
and plant material resistant of further breakdown. The principal
constituents are derivative of certain hemicelluloses, cellulose,
lignin and proteins.
In general, finished compost is characterized by following features:
Dark brown to black in color.
Practically insoluble in water, although a part may go in
to colloidal suspension.
Dissolves to a large extent in dilute alkali, sodium
pyrophosphate or ammonium oxalate solution to give dark
colored extract which can be further fractionated into humic,
fulvic and humin fraction.
Has a C/N ratio ranging 10 to 20 depending upon the
original material and the degree of humification.
Is not in a biochemical stable state but change in
composition through the activities of microorganisms as
long as environmental conditions such as moisture and
temperature are suitable until it is oxidized to inorganic salts,
carbon dioxide and water. Many specific humic and fulvic
acid decomposing bacteria and fungi have been found to be
involved in the biodegradation of humic substrates.
Exhibits a high capacity for cation exchange and for
water absorption with consequent swelling.
When compost is applied to the soil it has beneficial
effects both on the soil and on the growing vegetation. Its
fertilizer values include nitrogen. Phosphorus, potassium,
calcium and magnesium. In addition it also contains essential
trace elements for plant growth.
Its favorable effects upon soil fertility are greatly enhanced if it
is used in conjunction with mineral fertilizers.
Criteria: There are several tests by which the various stages
of the composting process and the condition of the compost can
be judged but no single method appears completely adequate.
From the point of view of the overall judgment of the final product
following test are useful:
Physical characteristics such as temperature, color,
texture and so on and the extent of solubility in sodium
hydroxide or sodium pyrophosphate solution.
C/N ratio, status of plant nutrient content and compost
value as shown by crop returns or plant test.
Absence of flies and odour and the sanitary quality, i.e.
from free from pathogens, parasites and weeds seed.
The farm, the garden or the rural compost operator generally
will not be interested in detailed tests other than those to confirm
that the material is safe from the health point of view and this can be judged from the temperature of the compost pile and that
it is satisfactory for soil improvement which is judged by the
physical appearance of the finished product for routine day to day
monitoring temperature, appearance odour and presence of flies
are the important observation to be made.
Temperature change: Temperature is the best indicator
of the process, aerobic composting and as to whether or not the
pathogen parasites and weed and seed have been destroyed. When
aerobic composting progresses there is a rapid rise from ambient
temperature to 55ᵒC to 65ᵒC in the first three to five days. High
temperature maintained several days during the active period
of decomposition provided that proper aeration and moisture
condition are maintained. The failure to attain thermophilic
temperature within three to six days shows that either the heap is
too small to retain the heat or moisture is excessive or insufficient
or carbon nitrogen relationships of the organic materials is to
wide or nutrient may not be present in correct amounts. Cooling
is reliable indicator of finished compost only if the material does
not re-heat after turning and moistening. The temperature of
the compost pile can be determined by accurate or approximate
Accurate determination of temperature with in a
thermometer: The checking of the temperature inside a compost
pile can be accurately done with the use of a long stem dial
thermometer with provision for recording composting mass.
The procedure is quite satisfactory for rural community compost
operation and metal dial thermometer with a stem of 0.5 to 0.75
m length is satisfactory and will not easily break.
The compost heap is dug into at several places and
temperature inside felt by hand. If thermophilic temperature
has been developed the material will feel very hot to the hand
and will be too hot if the hand is kept in the heap for very long.
In winter or at low ambient temperature when the pile is
opened during period of high temperature, steam will be seen
The temperature inside compost can also be approximated
by inserting a metal rod about 0.75 m long into it for about five
or ten minutes. On removing the rod it will be hot to the touch
and thermophilic temperatures may be too hot to hold.
These approximate testing measures for temperature will
be satisfactory for small rural composting or for individual
farmers composting small amounts of organic residues. However,
temperature alone cannot indicate the progress of composting
because sometimes the drop in temperature may result from the
development of unfavorable environmental condition such as
moisture, aeration and thermal kill of organisms.
Physical characteristics of finished compost:
Structure: The material should be crumbly it should be
medium loose not packed and not lumpy.
Color: A blackish brown color is the best. A pure black
color shows unfavorable fermentation with too much moisture
and lack of air. A grayish, yellowish color indicates an excess of
sol or ash. When the material inside the biomass decomposes
an aerobically, it turns pale green and shows little change with
progressive composting. Aerobic composting is characterized by
a progressive darkening of color.
Moisture Status: The approximate moisture status of
the compost can be judged by inserting an iron rod to different
depths in the pile. The rod should become quite moist if sufficient
moisture is being maintained. The moisture status can also be
judged simply by visual observation. No water should drip from a
sample of compost if pressed by hand.
Odour: The odour should be like humus or soil. Any foul
smell is a sign that decomposition is not yet complete and that
breakdown processes are still going on. Anaerobic condition can
easily be detected by disturbing the heap.
Acidity: A neutral to slightly acid reaction is the best
although slight alkalinity is acceptable. A too acidic reaction
indicates lack of aeration and too much moisture. The pH range
for good compost is between 6.0 and 7.5 Nitrogen-fixing bacteria
can thrive well at this pH range.
The proper moisture and proportion of raw material
determines the C/N ratio and fertilizer value of compost. A
compost with an organic matter content as low as 8% is little more
than a soil rich in humus as generally found in temperate region.
On average, compost should have about 30% to 60% organic
matter in the final material. Chemical tests such as determination
of carbon and nitrogen and the C/N ratio a more reliable indicator
of the finished product, however, if a C/N ratio of 20 or less is
attained, normal compost is considered as ready for use. However,
the C/N ratio of a well composted material may vary between 5,
50 and 20.
Novel approaches to improve the process of composting,
including reducing generation time, inclusion of fecal residues/
animal litter, organic/ inorganic compounds and consortia of
effective microorganisms has revolutionized the use of compost
in diverse spheres of agriculture and made it an essential
component in crop-production, crop- protection and natural
resource management. Keeping in view the different agro-climatic
zones, tailor made bioinoculants and technologies are needed to suit the demands of the local farmers for quality compost
production. Although lot of work has been done on microbiology of
composting, there is lack of sufficient knowledge about microbial
diversity and their exact role during various stages of composting.
There is a strong need to carry out work on the unculturable
microorganisms and their activities during the composting
processes using advanced techniques like denaturing gradient
gel electrophoresis (DGGE) and other cultivation independent
techniques. Extension workers and KVKs need to play a major role
in popularizing different compost technologies among farmers.
Besides composting, agro wastes may be utilized as a useful
resource for production of animal feed, biofuel and enzymes to
generate additional income from bioconversion process.