Nitrogen Losses |1.Leaching loss 2.Runoff loss 3.Gaseous loss Gaseous loss- Volatilization, Chemical decomposition, Denitrification | Explained

1. Nitrogen Losses
• Leaching loss/Drainage loss of NO3
-
 leaching is the loss of water-soluble
plant nutrients from the soil, due
to rain and irrigation.
• Runoff loss like of NH3.
• Gaseous losses
1) Volatilization
2) Chemical decomposition
3) Microbial Denitrification

2. 1. Volatilization or non-biological loss of NH3 :
when pH >8 , N2 is lost in the form of NH3 in alkaline medium.-
NH4
+OH- + H2O  NH3 + 2 H2O
60% N-loss in India is due to volatilization . Hence in alkali soil, the N-application is
raised at least by 25% .
2. Chemical decomposition of NO2
- under acid conditions to yield nitrogen and nitrogen
oxide. This loss takes place when pH is 5.5 or low under aerobic condition.
There are 3-mechanisms-
(i) Decomposition of NH4 NO2
NH4 NO2 2 H2O + N2

3. (ii) Van slyke reaction-
R-NH2 + HNO2  R-OH + H2O + N2
(iii) Spontaneous decomposition of Nitrous acid
3 HNO2  H2O + 2NO + HNO3
NO + O  NO2
2HNO2  NO + NO2 + H2O
NO is unstable under aerobic condition and immediately converted to NO2.

4. 3. Microbial Denitrification :
 Leading to liberation of N2 and N2O.
 Formation and loss of gaseous form of N by biological reduction of NO3
- and NO2
- is known
as Denitrification.
 Oxidation of NH3 to NO3
- and NO-
2 and oxidation of carbon compounds run simultaneously
as long as supply of elemental O2 is present.
 In the absence of elemental O2 , NH +
4 oxidation ceases.
 Certain organisms like Pseudomonas denitrificans ( gram negative), Achromobactor, Bacillus, Micrococcus
; are capable of using oxygen derived from nitrite and nitrate or both in place of elemental
oxygen. Removal of oxygen from NO-
3 and NO-
2 reduces the substances chemically .
 The products of the reductions are mostly gaseous form of nitrogen including nitrous oxide
(N2O), nitric oxide (NO) and elemental Nitrogen (N2).
-2[O] -2[O] -[O] -[O]
2HNO3 ---------> 2HNO2 ---------> 2NO -------> N2O -------> N2

5.  Waterlogging induces denitrification. Denitrification losses can be reduced by addition of
phosphate residues, by providing adequate drainage and with availability of excess accumulation
of active nitrogen compounds in the soil.
• After ratoon crop wheat yield is more due to availability of phosphatic fertilizer which is left as
residue in the ratoon sugarcane and organic matter content is also high due to sugarcane ratoon

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