Soil Fertility and Nutrient management (1+1)

Major Process of organic matter decomposition

Decomposition processes
Two major decomposition processes involved
1. Mineralization
2. Immobilization

1. Mineralization Is the conversion of an element from organic form to an inorganic/mineral form is called mineralization. Mineralization occurs for each element present in the organic matter individually especially for N, P and S
A. Nitrogen mineralization:
It is the conversion of organic nitrogen into inorganic Nitrogen NH4 and NO3 by microorganisms
Organic N(proteins and amino acids)  ----------> Proteose------------>Peptone-------------->Amino compounds- ammonia -----------> nitrite --------> nitrate
Different steps involved in N-mineralization
1. Aminisation: proteins and other complex nitrogenous compounds are converted into amino acids and amino compounds by the action of enzymes and microorganisms, CO2 and energy is released.
2. Ammonification: it is the biochemical conversion of amino compounds and amino acids into ammonia by bacterial decomposition.



This process is governed by aminase and deaminase enzymes. The liberated NH3 is utilized by plants.
3. Nitrification :It is the biochemical oxidation of ammonia into nitrite and then finally into nitrate. This process carried out by by autotropic bacteria (Nitrosomanas and Nitrobacter) in aerobic condition. Two steps are involved



Rate of nitrification depends on suitable temperature, humidity, pH, season, aeration, addition of lime (increases), nature of organic matter etc.
4. Denitrification :It is the biochemical reduction of nitrate or nitrite to gaseous nitrogen (N2), either as molecular N or oxides of N.



Loss of nitrate by reduction and assimilation
B. Phosphorus mineralization
• The process of conversion of organic forms of P into inorganic forms of P by P decomposing microorganisms especially by micorrhiza species is known as P-mineralization.
• The organic-P found in organic manures mainly as nucleic acids, phytin, phospho lipids, inositol PO4, lecithin etc. The organic P is not directly available to plants and it has to undergo decomposition by micro organisms especially mycorrhyzal species.

C. Sulphur mineralization
• The organic forms of S compounds such as methionine, cystine, cysteine are converted into inorganic sulphate forms (available) by aerobic bacteria species especially Thiobacillus and thiobacter.  

2. ImmobilizationThe conversion of an element from the inorganic to the organic form in microbial tissues or in plant tissues, thus rendering the element not readily available to other organisms or to plants.
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