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Chapter: 11th Microbiology : Environmental Microbiology

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Compost is organic matter that has been decomposed and recycled as a fertilizer and soil amendment.


Compost is organic matter that has been decomposed and recycled as a fertilizer and soil amendment. It is a mass of rotted organic matter made from waste. Example: garbage, paper, sugarcane trash, paddy straw, aquatic weeds, other agricultural waste.

Composting is a natural process in which aerobic and anaerobic microorganisms decomposes organic matter into valuable manure called as compost. The primary objective of composting is to convert an unstable material into stable end product (Figure 9.11).


The humification of organic material occurs in three stages

1. Mesophilic stage - Mesophilic is the initial stage of decomposition, lasting for about a week, during which sugars and other simple carbohydrates are rapidly metabolized. This is an exothermic process and may cause an increase in temperature by 40°C. Example: Bacillus subtilis

2. Thermophilic stage - Thermophilic is the second stage, lasting for about two weeks, during which the temperature may rise to about 50 to 75°C. Such a drastic increase in temperature is accompanied by the decomposition of cellulose and other resistant materials. It is important that the material be thoroughly mixed and kept aerated during this stage. Example: Bacillus stearothermophilus

3. Curing stage - The temperature decreases during this final stage and the material being composted is recolonized by mesophillic organisms, which often produce plant-growth stimulating compounds.


The humification of organic material is characterized by an increase in concentration of humic acids approximately from 4 to 12 percent, and decreases during the composting process.


Compost bed types

1. Pit method

2. Heap method


Pit method

The compost pits dug in soil with dimension of 3.5m x 2.5m x 1.5m (LxBxH). 

The pits are filled layer by layer using green plants and animal excreta. The layering is repeated until the pit is filled. Finally a layer of mud is plastered on the top of the pit (Figure 9.12).


Heap method

In regions with heavy rainfall, the compost may be prepared in heaps above the ground level and protected by a shed. The pile is made with dimension of 2m x 2m x 1.5m (LxBxH) (Figure 9.13).


Methods of compost preparation

1. Indore method

2. Bangalore method


Indore method

This method was developed at Indore, India. In this method organic wastes are spread in the cattle shed to serve as bedding. Trenches are dug with dimension of 10ft x 6ft x 2ft.

Dry wastes with cattle dung and soil are added in ratio of 4: 2: 1 up to 2 inches layer in composting pit. A moisture level of about 40-50% is ideal for good composting. Odour and insect problems can be controlled by covering the piles with a layer of soil or wood chips.

The heap is left undisturbed for about 8 to 9 months. Turning the pile for every 15 days is important for coplete composting because pile needs a periodic influx of O2. Plant residues, weeds, sugarcane leaves, grass, wood ashes, animal dung, and water urine soaked mud can also be used as raw materials for this type of composting.


Bangalore method

·        This method was developed at Bangalore, India. It is recommended as a satisfactory method for disposal of town wastes and night soil.

·        The compost pits dug in soil with dimension of 4.5m x 2.5m x 90cm (LuBuH)

·        In the Bangalore method of composting, dry waste material of 25cm 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 alternatively with dry layer of material and cow dung suspension till it rises 0.5m above the ground level and plastered with wet mud and left undisturbed for about 4-6 months or till required.

·        This method saves labour cost because there is no need of turning & regular sprinkling of water.


Benefits of compost

·        Compost improves the quality of soil hence called as a soil conditioner.

·        Compost contains a variety of the basic nutrients required for healthy growth of the plant.

·        Nitrogen, phosphorous, potassium and certain micronutrients viz, manganese, copper, iron and zinc are found in compost.

·        The composted product is safe and easy to handle, and does not induce nitrogen deficiency in recipient plants by nitrogen stabilization in the compost.

·        It  suppresses  disease  infestation  by partial sterilization and detoxifies pollutants.

·        Compost material is principally used for the reclamation of drastically disturbed. Example: mined soil, landscaping and agriculture.

·        Compost finds unrestricted application in parks and gardens for ornamental plants, in land reclamation and highway beautification projects.


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