The decomposition of organic wastes in soil occurs naturally at ambient temperature to produce humus. The humification process occurs very slowly in soil. It takes nature 2000 years to produce 10 cm high of humus. This natural decomposition process in the soil can be regulated and speeded up by man.

Here, organic materials are collected and gathered together into a heap so that the heat that evolved from the process is saved. As a result, the temperature of the heat rises thereby speeding up the basic degradation process of nature, which normally occurs slowly in organic wastes that fall on the surface of the ground. The final product of the process is called compost or humus.

Therefore, Composting is the decomposition or breakdown of organic waste materials by a mixed population of microorganisms in a warm, moist, and aerated environment. It involves creating humus-like organic materials outside the soil by mixing, piling, or storing organic materials under conditions conducive to aerobic decomposition and nutrient conservation.

Process of Composting

Composting process is most commonly used to change waste organic materials into useful products. The waste material will normally have within it a variety of microorganisms capable of carrying out the process.

When the material is exposed to the air and moisture content brought to a suitable level, the microorganisms begin their work. In addition to oxygen from the air and moisture, the microorganism requires, for their growth and reproduction, a supply of food containing carbon and nutrient such as nitrogen, phosphorus, and potassium. Waste materials usually provide these food requirements.

A good composting process should pass through 3 consecutive stages:

Heating phase (fermentation)
Cooling phase
Maturation phase.

Read Also: Role of Organic Matter in Soil Fertility

a) Heating phase

During this stage, which is the first stage of composting, the heap starts to build up considerably. This is known as fermentation and is the result of the breaking down of complex and tough fibrous material of organic matter. For effective fermentation:

The compost heap should be made of all sorts of materials;
- Right microorganisms have to be present;
- Adequate air and water

If the above three conditions are met heat will be generated quickly. During fermentation, the microorganisms multiply and change rapidly which adds up to the heating process. Fermentation may reach 60 – 70˚C in the compost heap.

Fermentation has hygienic effects as it destroys pathogens. It is important that the temperature of the heap be tested to make sure that fermentation is taking place.

A simple way of testing if the fermentation process is taking place is by putting a stick at the center of the heap after completion and leaving it until the next day.

After taking it out, feel it immediately. It should be considerably warmer than body temperature. If not, then this is an indication that something is wrong with the heap.

b) Cooling down phase

During this stage, the temperature drops to near ambient because of exhaustion of high-energy compounds in the compost pile.

Compost is recolonized by new microorganisms including beneficial organisms producers of plant-growth stimulating compounds or antagonistic to plant pathogens.

The decomposition process is slower but the chemical reactions continue which stabilize the hummus. This phase of composting can last several weeks to months.

c) Maturation phase

This is the last stage of composting. Here the temperature drops to soil temperature depending on the climate. Apart from the soil microorganism such as bacteria and fungi, large soil microfauna is also active at this stage.

In temperate environments, earthworms feed strongly on the decomposed organic material and this helps in the decomposition process.