Decomposition of Organic Residues: 3 Mechanisms

This article throws light upon the three mechanisms of decomposition of organic residues. The mechanisms are: 1. Enzymes and the Biological Reaction 2. Simple Products of Decomposition 3. Decomposition Action

Mechanism # 1. Enzymes and the Biological Reaction:

An enzyme is a substance, composed of protein that is capable of lowering the activation energy of other selective compounds enough to allow the breaking of a particular bond under a particular environment. So such reactions influenced by enzymes are called biological reactions.

The action of enzymes to make a split easier does not “use up” the enzyme. When one reaction is completed, the changed molecule diffuses into the solution and the enzyme then can split another similar bond.

An activator that is not consumed or changed by such a process is called catalyst. Many different enzymes are produced by a single organism and many organisms produce the same enzyme. A list of common enzymes with their particular reactions is given in Table 19.1.

Various other enzymes are present free in the soil for a short time when living cells are ruptured or when they die and their enclosing membranes decompose.

Mechanism # 2. Simple Products of Decomposition:

When organic residues undergo decomposition under aerobic and anaerobic soil conditions the end products will be different which follow are:

Mechanism # 3. Decomposition Action:

The death of organisms eventually results in the rupture of cell membranes and the dissolution of many soluble cell substances that then move into the soil and water solution.

The organic solid (non-water portion of a dead organism) are changed only very slowly until micro­organisms attack them. Bacteria, fungi and other micro-organisms that effect decomposition excrete a variety of enzymes to initiate break-down of the organic material.

Microbes absorb the nutrients released during decomposition—especially nitrogen and carbon and use them for growth and reproduction. The rate of decomposition is directly proportional to the numbers of microbes present, so once decomposition starts; it progresses more quickly as newly multiplied micro-organisms also start the work of decomposition.

‘The nitrogen content in the microbes and in the organic residues is given in proportion to the carbon content and that is called Carbon: Nitrogen (C: N ratio) ratio. Bacteria require one pound of nitrogen for each four or five pounds of carbon (C: N ratio of 4 or 5: 1), are heavy users of nitrogen.

If a paddy straw having wider C: N ratio (about 80: 1, C: N ratio) is incorporated into a soil, the population of bacteria will increase slowly because the straw is a low nutrient food for the micro-organisms.

The process of decomposition can be accelerated by adding more nitrogen to supply foods for microbes and plants. A wide C: N ratio organic materials when applied to soils containing low nitrogen, the plants will suffer due to nitrogen deficiency because soil micro-organisms are able to use most available nitrogen before it will become accessible to plant root surfaces.

The same situation is applicable to phosphorus, sulphur and other nutrient elements in organic materials and soil. With the progress of decomposition, more amount of CO₂ released into the atmosphere. This narrows the C: N ratio in the organic matter (which includes microbe bodies) because a very little amount of nitrogen is lost as compared to large amounts of carbon volatilized.

Therefore, the food and energy is in short supply and some of the micro-organisms like bacteria and fungi die. Other micro-organisms decompose their bodies containing high amount of nitrogen and liberation of available nitrogen into the soil solution and evolution of CO₂ take place. This released nitrogen is then available to plants.