Composting - an overview
Composting is the natural process of 'rotting' or decomposition of
organic matter by microorganisms under controlled conditions. Raw organic
materials such as crop residues, animal wastes, food garbage, some municipal
wastes and suitable industrial wastes, enhance their suitability for
application to the soil as a fertilizing resource, after having undergone
composting.
A mass of rotted organic matter made from waste is called compost.
The compost made from farm waste like sugarcane trash, paddy straw, weeds and
other plants and other waste is called farm compost. The average nutrient
contents of farm compost are 0.5 per cent N, 0.15 per cent P2O5and 0.5 per cent
K2O. The nutrient value of farm compost can be increased by
application of superphosphate or rock phosphate at 10 to 15 kg/t of raw
material at the initial stage of filling the compost pit. The compost made from
town refuses like night soil, street sweepings and dustbin refuse is called
town compost. It contains 1.4 per cent N, 1.00 per cent P2O5 and 1.4 per cent
K2O.
Farm compost is made by placing farm wastes in trenches of
suitable size, say, 4.5 m to 5.0 m long, 1.5m to 2.0 m wide and 1.0 m to 2.0 m
deep. Farm waste is placed in the trenches layer by layer. Each layer is well
moistened by sprinkling cow dung slurry or water. Trenches are filled up to a
height of 0.5 m above the ground. The compost is ready for application within
five to six months.
Composting is essentially a microbiological decomposition of
organic residues collected from rural area (rural compost) or urban area (urban
compost).
Methods of composting
In Coimbatore method, composting is done in pits of
different sizes depending on the waste material available. A layer of waste
materials is first laid in the pit. It is moistened with a suspension of 5-10
kg cow dung in 2.5 to 5.0 I of water and 0.5 to 1.0 kg fine bone meal sprinkled
over it uniformly. Similar layers are laid one over the other till the material
rises 0.75 m above the ground level. It is finally plastered with wet mud and
left undisturbed for 8 to 10 weeks. Plaster is then removed, material moistened
with water, given a turning and made into a rectangular heap under a shade. It
is left undisturbed till its use.
In the Indore method of composting, organic
wastes are spread in the cattle shed to serve as bedding. Urine soaked material
along with dung is removed every day and formed into a layer of about 15 cm
thick at suitable sites. Urine soaked earth, scraped from cattle sheds is mixed
with water and sprinkled over the layer of wastes twice or thrice a day.
Layering process continued for about a fortnight. A thin layer of well
decomposed compost is sprinkled over top and the heap given a turning and
reformed. Old compost acts as inoculum for decomposing the material. The heap
is left undisturbed for about a month. Then it is thoroughly moistened and
given a turning. The compost is ready for application in another month.
In the Bangalore method of composting, dry waste
material of 25 cm thick is spread in a pit and a thick suspension of cow dung
in water is sprinkled over for moistening. A thin layer of dry waste is laid
over the moistened layer. The pit is filled alternately with dry layers of
material and cow dung suspension till it rises 0.5 m above ground level. It is left
exposed without covering for 15 days. It is given a turning, plastered with wet
mud and left undisturbed for about 5 months or till required.
In Coimbatore method, there is anaerobic decomposition to start
with, following by aerobic fermentation. It is the reverse in Bangalore method.
The Bangalore compost is not so thoroughly decomposed as the Indore compost or
even as much as the Coimbatore compost, but it is bulkiest.
Compost is a rich source of organic matter. Soil organic matter
plays an important role in sustaining soil fertility, and hence in sustainable
agricultural production. In addition to being a source of plant nutrient, it
improves the physico-chemical and biological properties of the soil. As a
result of these improvements, the soil:
(i) becomes more resistant to stresses such as drought, diseases
and toxicity;
(ii) helps the crop in improved uptake of plant nutrients; and
(iii) possesses an active nutrient cycling capacity because of vigorous microbial activity.
(ii) helps the crop in improved uptake of plant nutrients; and
(iii) possesses an active nutrient cycling capacity because of vigorous microbial activity.
These advantages manifest themselves in reduced cropping risks,
higher yields and lower outlays on inorganic fertilizers for farmers.
Dung and urine produced by animals per day
|
Animal
|
Urine
(ml / kg live wt) |
Quantity of dung (Kg) per day
|
|
Horse
|
3-18
|
9-18
|
|
Cattle
|
17-45
|
18-30
|
|
Buffaloes
|
20-45
|
25-40
|
|
Sheep and goats
|
10-40
|
1-2.5
|
|
Pigs
|
5-30
|
3-5
|
|
Poultry
|
-
|
2.5-3.5
|
Nutritive value of animal solid and liquid excreta
|
Animal
|
Dung (mg/g)
|
Urine (%)
|
||||
|
N
|
P
|
K
|
N
|
P
|
K
|
|
|
Cattle
|
20-45
|
4-10
|
7-25
|
1.21
|
0.01
|
1.35
|
|
Sheep and goat
|
20-45
|
4-11
|
20-29
|
1.47
|
0.05
|
1.96
|
|
Pig
|
20-45
|
6-12
|
15-48
|
0.38
|
0.1
|
0.99
|
|
Poultry
|
28-62
|
9-26
|
8-29
|
-
|
-
|
-
|
Why composting is necessary?
- The rejected biological
materials contain complex chemical compounds such as lignin, cellulose,
hemicellulose, polysaccharides, proteins, lipids etc.
- These complex materials cannot
be used as such as resource materials.
- The complex materials should be
converted into simple inorganic element as available nutrient.
- The material put into soil
without conversion will undergo conversion inside the soil.
- This conversion process take
away all energy and available nutrients from the soil affecting the crop.
- Hence conversion period is
mandatory.
Advantages of Composting
- Volume reduction of waste.
- Final weight of compost is very
less.
- Composting temperature kill
pathogen, weed seeds and seeds.
- Matured compost comes into
equilibrium with the soil.
- During composting number of
wastes from several sources are blended together.
- Excellent soil conditioner
- Saleable product
- Improves manure handling
- Redues the risk of pollution
- Pathogen reduction
- Additional revenue.
- Suppress plant diseases and
pests.
- Reduce or eliminate the need
for chemical fertilizers.
- Promote higher yields of
agricultural crops.
- Facilitate reforestation,
wetlands restoration, and habitat revitalization efforts by amending
contaminated, compacted, and marginal soils.
- Cost-effectively remediate
soils contaminated by hazardous waste.
- Remove solids, oil, grease, and
heavy metals from stormwater runoff.
- Capture and destroy 99.6
percent of industrial volatile organic chemicals (VOCs) in contaminated
air.
- Provide cost savings of at
least 50 percent over conventional soil, water, and air pollution
remediation technologies, where applicable.
Drawbacks of Using Composts
Agricultural use of composts remains low for several reasons:
Agricultural use of composts remains low for several reasons:
- The product is weighty and
bulky, making it expensive to transport.
- The nutrient value of compost
is low compared with that of chemical fertilizers, and the rate of
nutrient release is slow so that it cannot usually meet the nutrient
requirement of crops in a short time, thus resulting in some nutrient
deficiency
- The nutrient composition of
compost is highly variable compared to chemical fertilizers.
- Agricultural users might have
concerns regarding potential levels of heavy metals and other possible
contaminants in compost, particularly mixed municipal solid wastes. The
potential for contamination becomes an important issue when compost is
used on food crops.
- Long-term and/or heavy
application of composts to agricultural soils has been found to result in
salt, nutrient, or heavy metal accumulation and may adversely affect plant
growth, soil organisms, water quality, and animal and human health
Composting organic materials with high lignin content - lime
treatment
- By adding organic wastes such
as sawdust, wood shavings, coir pith, pine needles, and dry fallen leaves,
while preparing organic waste mixtures for composting, one can ensure that
the compost produced contains sufficient and long-lasting humus. However,
gardeners often find that where they use lignin-rich plant materials, the
compost does not ripen rapidly. A technique for making good compost from
hard plant materials involves mixing lime in a ratio of 5 kg per 1000 kg
of waste material. Lime can be applied as dry powder or after mixing with
a sufficient quantity of water. Treatment with lime enhances the process
of decomposition of hard materials.
- Liming can enhance the
humification process in plant residues by enhancing microbial population
and activity and by weakening lignin structure. It also improves the humus
quality by changing the ratio of humic to fulvic acids and decreases the
amount of bitumen, which interferes with the decomposition process.
Instead of lime, powdered phosphate rock can be used in a ratio of 20 kg
per 1 000 kg of organic waste. Phosphate rock contains a lot of lime. The
phosphates and micronutrients contained in phosphate rock make composts
rich in plant nutrients.
Composting weeds
- This method has been developed
for composting weeds such as parthenium, water hyacinth (Eichornia
crassipes), cyperus (Cyperus rotundus) and cynodon (Cynodon
dactylon).
Materials Required
- 250 g of Trichoderma
viride and Pleurotus sajor-caju consortia, and 5
kg of urea. An elevated shaded place is selected, or a thatched shed is
erected. An area of 500 cm × 150 cm is marked out. The material to be
composted is cut to 10-15 cm in size. About 100 kg of cut material is
spread over the marked area. About 50 g of microbial consortia is
sprinkled over this layer. About 100 kg of weeds are spread on this layer.
One kilogram of urea is sprinkled uniformly over the layer. This process
is repeated until the level rises to 1 m. Water is sprinkled as necessary
to maintain a moisture level of 50-60 percent. Thereafter, the surface of
the heap is covered with a thin layer of soil. The pile requires a
thorough turning on the twenty-first day. The compost is ready in about 40
days.
Compost enrichment
Farm compost is poor in P content (0.4-0.8 percent). Addition of P
makes the compost more balanced, and supplies nutrient to micro-organisms for
their multiplication and faster decomposition. The addition of P also reduces N
losses. Compost can be enriched by:
- Application of superphosphate,
bonemeal or phosphate rock: 1 kg of superphosphate or bonemeal is applied
over each layer of animal dung. Low-grade phosphate rock can also be used
for this purpose.
- Use of animal bones: these can
be broken into small pieces, boiled with wood ash leachate or lime water
and drained, and the residue applied to the pits. This procedure of
boiling bones facilitates their disintegration. Even the addition of raw
bones, broken into small pieces and added to the pit, improves the
nutrient value of compost significantly.
- Wood ash waste can also be
added to increase the K content of compost.
- Addition of N-fixing and
P-solubilizing cultures (IARI, 1989): The quality of compost can be
further improved by the secondary inoculation of Azotobacter,Azospirillum
lipoferum, and Azospirillum brasilence (N-fixers);
and Bacillus megaterium or Pseudomonas sp.
(P solubilizers). These organisms, in the form of culture broth or water
suspension of biofertilizer products, can be sprinkled when the decomposing
material is turned after one month. By this time, the temperature of the
compost has also stabilized at about 35 °C. As a result of this
inoculation, the N content of straw compost can be increased by up to 2
percent. In addition to improving N content and the availability of other
plant nutrients, these additions help to reduce the composting time
considerably.
The Benefits of Using Composts to Agriculture
Compost has been considered as a valuable soil amendment for
centuries. Most people are aware that using composts is an effective way to
increase healthy plant production, help save money, reduce the use of chemical
fertilizers, and conserve natural resources. Compost provides a stable organic
matter that improves the physical, chemical, and biological properties of
soils, thereby enhancing soil quality and crop production. When correctly
applied, compost has the following beneficial effects on soil properties, thus
creating suitable conditions for root development and consequently promoting higher
yield and higher quality of crops.
Improves the Physical Properties of Soils
- Reduces the soil bulk density
and improves the soil structure directly by loosening heavy soils with
organic matter, and indirectly by means of aggregate-stabilizing humus contained
in composts. Incorporating composts into compacted soils improves root
penetration and turf establishment.
- Increases the water-holding
capacity of the soil directly by binding water to organic matter, and
indirectly by improving the soil structure, thus improving the absorption
and movement of water into the soil. Therefore, water requirement and
irrigation will be reduced.
- Protects the surface soil from
water and wind erosion by reducing the soil-dispersion action of beating
raindrops, increasing infiltration, reducing water runoff, and increasing
surface wetness. Preventing erosion is essential for protecting waterways
and maintaining the quality and productivity of the soil.
- Helps bind the soil particles
into crumbs by the fungi or actinomycetes mycelia contained in the compost
and stimulated in the soil by its application, generally increasing the
stability of the soil against wind and water erosion.
- Improves soil aeration and thus
supplies enough oxygen to the roots and escapes excess carbon dioxide from
the root space.
- Increases the soil temperature
directly by its dark color, which increases heat absorption by the soil, and
indirectly by the improved soil structure.
- Helps moderate soil temperature
and prevents rapid fluctuations of soil temperature, hence, providing a
better environment for root growth. This is especially true of compost
used as a surface mulch.
Enhances the Chemical Properties of Soils
- Enables soils to hold more
plant nutrients and increases the cation exchange capacity (CEC), anion
exchange capacity (AEC), and buffering capacity of soils for longer
periods of time after composts are applied to soils. This is important
mainly for soils containing little clay and organic matter.
- Builds up nutrients in the
soil. Composts contain the major nutrients required by all plants [N,P,K,
calcium (Ca), magnesium(Mg), and S] plus essential micronutrients or trace
elements, such as copper (Cu), zinc (Zn), iron (Fe), manganese (Mn), boron
(B), and molybdenum (Mb).
- The nutrients from mature
composts are released to the plants slowly and steadily. The benefits will
last for more than one season.
- Stabilizes the volatile nitrogen
of raw materials into large protein particles during composting, thereby
reducing N losses.
- Provides active agents, such as
growth substances, which may be beneficial mainly to germinating plants.
- Adds organic matter and humus
to regenerate poor soils.
- Buffers the soil against rapid
changes due to acidity, alkalinity, salinity, pesticides, and toxic heavy
metals.
Improves the Biological Properties of Soils
- Supplies food and encourages
the growth of beneficial microorganisms and earthworms.
- Helps suppress certain plant
diseases, soil borne diseases, and parasites.
- Research has shown that
composts can help control plant diseases (e.g. Pythium root rot,
Rhizoctonia root rot, chili wilt, and parasitic nematode) and reduce crop
losses. A major California fruit and vegetable grower was able to cut
pesticide use by 80% after three years of compost applications as part of
an organic matter management system. Research has also indicated that some
composts, particularly those prepared from tree barks, release chemicals
that inhibit some plant pathogens. Disease control with compost has been
attributed to four possible mechanisms:
- 1) successful competition for
nutrients by beneficial microorganisms;
2) antibiotic production by beneficial microorganisms;
3) successful predation against pathogens by beneficial microorganisms;
4) activation of disease-resistant genes in plants by composts; and
5) high temperatures that result from composting kill pathogens. - Reduces and kills weed seeds by
a combination of factors including the heat of the compost pile, rotting,
and premature germination.
Economic and Social Benefits of Composting
The economic and social benefits of composting include the
following:
- Brings higher prices for
organically grown crops.
- Composting can offer several
potential economic benefits to communities:
- Extends current landfill
longevity and delays the construction of a more expensive replacement
landfill or incinerator.
- Reduces or avoids landfill or
combustor tipping fees, and reduces waste disposal fees and long-distance
transportation costs.
- Offers environmental benefits
from reduced landfill and combustion use.
- Creates new jobs for citizens.
- Produces marketable products
and a less-cost alternative to standard landfill cover, artificial soil
amendments, and conventional bioremediation techniques.
- Provides a source of plant
nutrients and improves soil fertility; results in significant cost savings
by reducing the need for water, pesticides, fungicides, herbicides, and
nematodes.
- Used as an alternative to
natural topsoil in new construction, landscape renovations, and container
gardens. Using composts in these types of applications is not only less
expensive than purchasing topsoil, but it can also often produce better
results when establishing a healthy vegetative cover.
- Used as mulch for trees,
orchards, landscapes, lawns, gardens, and makes an excellent potting mix.
Placed over the roots of plants, compost mulch conserves water and
stabilizes soil temperatures. In addition, it keeps plants healthy by
controlling weeds, providing a slow release of nutrients, and preventing
soil loss through erosion.
