Mineralization of organic nitrogen

Mineralization of Organic Nitrogen-
1.Aminization 2.Ammonification 3.Nitrification

1. Aminization Ammonification Nitrification
Anaerobic
Mediated by heterotrophic bacteria
Aerobic
Mediated by autotrophic bacteria
Mineralisationof Organic Nitrogen :
Mineralisation–conversion of an element from an immobilized form to
an available form as a result of microbial decomposition.

2. 1. Aminization:
•Hydrolytic decomposition of protein and release of amines and amino acids by
heterotrophs (bacteria like Bacillus, Pseudomonas) in absence of O
2.
O.M.---------------> Polypeptides
Polypeptides/Proteins ---------> R-NH
2+CO
2 + Energy + other compounds.
hydrolysis

3. 2. Ammonification :
•The amines and amino acids so released are further utilisedby other hetrotrophsby
release of ammonicalcompounds in absence of O
2.
R-NH
2+ HOH --------> NH
3 + R-OH + Energy
2NH
3 + H
2CO
3--------> (NH
4)
2CO
32NH
+
4 + CO
3
2-
NH
3so released are subjected to several fates—
(a) may be converted to Nitrites and Nitrates by nitrification.
(b) may be absorbed directly by higher plants.
(c) may be utilized by heterotrophs organisms in the further decom
position of O.M.

4. (d) may be fixed in a biologically unavailable form (in subsoil about 40-50% and in top
soils 6 %) in the lattice of certain expanding type of clay-minerals like
momtmorillonite, illiteand vermiculite.
3. Nitrification :
•By autotrophs in presence of O
2i.e. biological oxidation. According to Winogradsky
(1889), NH
3or NH
+
4salt in the soil is oxidisedinto NO
-
3in two steps.
(i) NH
3 / NH
4
+
------------------------> NO
2
-
[Nitrite]
Nitrosomonasis Obligate parasite.
(ii) NO
2
-
---------------------> NO
3
-
[Nitrate]
[O]
Nitrosomonas
Nitrobacter
[O]

5. Opt. temperature for Nitrifying bacteria is 30-35°C and Opt. pH 6 .5-7.5. The
activity of bacteria ceases below pH 5.0.
Nitrobacteria = Nitrosomonas+ Nitrobacterboth.
Reactions:
2 NH
4
+
+ 3O
2---------------> 2NO
2
-
+ 2H
2O + 4H
+
+ Energy .
2 NO
2
-
+ O
2—---------> 2 NO
3
-
+ energy.
When NH
4
+
-Fertilizers are added to soil, three important inferences are drawn by
these nitrification equations –
(i) Reactions require molecular oxygen means nitrification takes place most readily in
well aerated soil.
(ii) Reactions release H
+
which results in acidification of soil.
(iii) Microbial activity hence their rapidity and extent of transformation will be greatly
influenced by soil environmental conditions such as moisture supply, temp etc.

6. Factors affecting Nitrification :
(i) Supply of NH
4
+
(ii) Population of nitrifying organisms
(iii) Soil reactions
(iv) Soil aeration
(v) Soil moisture
(vi) Soil temp. (30-35°C)
(vii) C : N ratio -
<20 favoursmineralization (release of NH
3& NO
3
-
)
>30 immobilization
15-30 or 20-30 -both
(viii) Fertility.

7. Thank You!