Decomposition is a process that break down, digest and recycle nutrients. It’s the physical breakdown and biochemical transformation of the substrate. Autolysis is a process that breaks down the tissue by its own enzyme and putrefaction is the process when the bacteria attacks the cells, both these process starts as soon as death takes place.
The soil macro-organisms, meso-organisms and microorganisms are the specific group of decomposers. The soil macro-organisms are earthworm, millipede, snails, slugs, etc., meso-organisms are spring tail, mites etc. and the soil microorganisms are bacteria, actinomycetes and fungi.
The organic matter consisting of biomolecules are initially fragmented by the macro and meso-organisms either by chewing, sucking or grinding. Following this the soil microorganisms will release enzyme to utilize this fragmented organic matter substrate thus biochemically transforming the substrate into a form that can be readily absorbed as a nutrient source and recycled. Earthworm while burrowing in soil, loosen the soil and gradually intake the soil along with the plant residues, digesting and producing waste known as casting. The microorganisms contained in the castings are fed by the protozoans and nematodes releasing the nutrients. Decomposition process leads to mineralization. The process that transforms the organic matter into mineral.
Different kinds of compound decompose at different rate. The chemical structure of the biomolecule affects the rate of decomposition. Simple organic compound break more easily such as sugars and proteins decompose rapidly as compared to cellulose and fats. Lignin amongst all organic compound decompose slowly because of its chemical complexity. Factors that affect the biological activity and the rate of decomposition are oxygen, moisture, temperature, pH, inhibitors, carbon-nitrogen ratio, and the nature of the substrate in soil.
Factors limiting the microbial activity are:
- Oxygen: The soil microorganisms obtain energy by oxidizing the carbon content of the organic matter. Decomposer consume more oxygen than the oxygen diffused into the soil. As a result oxygen level decreases creating condition that become unfavorable for aerobes to survive.
- Moisture: Decomposers need water. The microorganisms utilize organic molecule dissolved in water. High water content replaces oxygen of the soil pore spaces creating an unfavorable condition for the aerobes to survive thus favoring the growth of anaerobes. High moisture in soil limits gas exchange.
- Temperature: As the decomposers decompose the organic matter heat is generated which will alter the surrounding temperature affecting the microbial activity. Extreme temperatures slow down the soil microbial activity
Decomposition and microbial activity are affected by climate change. Organic matter decomposes faster in warm climate. Humus a product of decomposition may be oxidized further when amended in soil. The soil microorganisms do not have the ability to synthesize their own food therefore survive on carbon containing organic matter. The bacteria release organic acid which aid in solubilization of mineral element bound in soil and also release complex substances that build soil. The fungi too decompose the organic matter releasing the bound nutrient for other organisms and many of the organic compound released by fungi aids in forming humus and soil aggregate. The mycorrhizal fungi help plant root in absorbing phosphorous and some trace elements and beside this they form soil aggregate which gives soil a desirable soil structure.