Mineral Nutrition

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Atmospheric N2

Biological

N2 fixation

Industrial

N2 fixation

Electrical

N2 fixation

Denitrification

(Ammonification)

(Uptake)

Decaying biomass

Plant biomass

Animal biomass

Soil ‘N’ Pool

NO2

–

NH3

NO3

–

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Some of this ammonia volatilizes and re-enters atmosphere but most

of it is oxidised into nitrate by soil nitrifying bacteria (Nitrosomonas,

Nitrococcus & Nitrobacter-chemo-autotrophs).

(AIPMT 2011)

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These steps are called nitrification.

Nitrosomonas

Nitrococcus

NO2

–

NO2

–

H

+

H2O

O2

NH3

NH3

O2

O2

H2O

H

+

Nitrobacter

NO2

–

NO2

–

NO3

–

NO3

–

O2

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Plants absorb the nitrate and is transported to the leaves. In leaves, it is

reduced to form ammonia that finally forms the amine group of amino

acids

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Nitrate present in the soil is also reduced to nitrogen by the process of

denitrification It is carried by bacteria Pseudomonas and Thiobacillus.