Nitrogen

 Discovered by Daniel Rutherford of Great Britain

in 1772

Characteristics of nitrogen

• Belongs to group V-A in the periodic

table
• Highly reduced
•Nitrogen must combined with Hydrogen
and Oxygen to be reactive
• N as ammonium is easily fixed in clay
• 78% Nitrogen gas (N2) in the atmosphere
Functions of nitrogen in plants

1. Constituent of chlorophyll molecule

2. Constituent of amino acids, proteins and nucleic acids
(DNA/RNA
important in the synthesis of protein
3. Constituent of alkaloids (quinie, morphine,
nicotine, cocaine, and caffeine)
4. Associated with photosynthetic activity, vigorous vegetative
growth, dark green color of leaves and succulence of
tissues.
 Nitrogen

The Nitrogen Cycle

Additions of nitrogen into the soil from the cycle

 From industrial nitrogen fixation – Haber process

- Synthetic nitrogen fertilizers
 From biological nitrogen fixation
- Legume-Rhizobium symbiosis (ex. Rhizobia)
- Non-symbiotic nitrogen fixation (ex. Azotobacter)
 Rain
 Animal manures
 Green manures
Irrigation water
 Forms of Nitrogen in the soil

• total N= 0.02% - 0.4%

• Organic N= 95% of total N in the surface
• Inorganic N:
- NH4+, NO3- , NO2- - most important and 2-5% of total soil N
the rest are N2O (Nitrous oxide) NO (Nitric oxide) and N2
• Organic N:
- Protein, amino acids, amino sugars, nitrosamins, purines and
pyrimidine derivatives
 Forms of Nitrogen absorbed by plants
• Ammonium NH4+, and Nitrate NO3-
• Nitrate (NO3-) is more abundant in aerobic soils
• Most plant absorb both
• NH4+ abundant in reduced layer of paddy soils
• NH4+, is the preferred source since NO3-
reduction for protein synthesis needs 2 NADH
per NO3- reduced. At low pH NH4+ uptake is low
and high at neutral pH
 Losses of nitrogen from the cycle

• Gaseous loss - denitrification occur in lowland condition

-volatilization occur in upland condition
• Leaching- downward movement of nutrients
• Erosion- carried by water
• Ammonium fixation by 2:1 clay minerals
 Examples of Biological Nitrogen Fixation

Crops: Crops:
1.Food legumes 3. Pasture
•Cowpea • Stylosanthes
• Soybean • Sesbania
• Peanut • Crotolaria

Crops: Crops:
2. Trees 4. Azolla
• Ipil-Ipil • 450-600 kg N/ha/yr
• Acacia • Doubling time: 5-7 days
• Kakawate
Factors affecting Biological nitrogen fixation:

•Soil pH
• Concentration of nitrate, ammonium, nitrite and
urea
• Ca, P, K, Co, Mo (enhance fixation)
Nitrogen Containing Fertilizer Materials

Commercial name Analysis grade

Urea 46-0-0
Ammonium sulfate 21-0-0-24
Ammonium chloride 25-0-0
Di-ammonium phosphate 18-46-0
Ammonium phosphate 16-20-0
Complete 14-14-14
Additions in the Cycle
1. Rain – about 4-8 kg/ha/yr
2. Non-symbiotic or Asymbiotic N fixation
12-40 kg N/ha/yr in tropical rainforest
 14-70 kg N/ha/yr by blue green algae in paddy rice
3. Symbiotic N fixation
 Cowpeas – 58- 116 kg N/ha/yr
 Soybeans – 58-160 -do-
 Peanut – 42 -do-
 Kudzu – 107 -do-
Additions in the Cycle

4. Use of N containing fertilizer

 Ammonium sulfate, (NH4)2SO4 - 21 % N
 Urea, CO(NH2)2 - 46% N
 NH4Cl - 24% N
 Complete, 14-14-14
 Diammonium phosphate 18-46-0

 Ammonium phosphate 16-20-0

Additions in the Cycle
5. Animal Manures, Green Manures & Crop Residues
 Cattle manure – 3-4% N
 Carabao manure – 1.09% N
 Chicken manure – 3-4% N
 Swine manure - 2% N
 Mucuna - 3.3% N
 Ipil-ipil 2-4% N
 Peanut hay .8-1.8%
 Corn stover 0.5-1.0% N
 Rice straw 1.0 % N
 Symbiotic Nitrogen Fixation

2H+ + 2e- 2H+ + 2e- H2N-NH2

N N HN NH
Nitrogenase Diamide Hydrazine
2H+
+
2e-

2NH3
N2 + 6H+ + 6e- Ammonia
2NH3

Microsymbiont ------ Rhizobium sp.

Host Plant ------ Leguminosae

 Examples of Nitrogen Oxidation No.
Ammonia, NH3 -3
Nitrogen gas, N2 0
Nitrite, NO2- +3
Nitrate, NO3- +5

Examples of Nitrogen Fertilizers Analysis grade

Urea, CO(NH)2 46-0-0
Ammonium sulfate, (NH4)2SO4 21-0-0-24
Ammonium chloride, NH4Cl 26-0-0
Mono-ammonium phosphate, NH4H2PO4 16-20-0
Di-ammonium phosphate, (NH4)2HPO4 18-46-0
Complete 14-14-14
 Manufacture of Nitrogen Fertilizers

Raw Materials: NH3 and Acid

Manufacture of ammonia gas:

Reactants: Nitrogen gas and Hydrogen gas

Source of nitrogen gas:

1. Atmosphere ……. 78% N
36,000 tons of N over 0.4 hectare of land
and water

Sources of hydrogen gas

1. Water gas reaction – reacting heated carbon “coke”
with superheated steam
C + HOH CO + H2
Sources of hydrogen gas:
2. Natural gas – hydrogen is produced by reacting methane
(the principal component in natural gas feedstock)
with steam, using Nickel as catalyst and at 700oC
and 14 psi
CH4 + H2O CO + H2
CO + H2O CO2 + H2

Note: CO2 is removed by using monoethanolamine and

hot potassium carbonate
CO is removed by using cuprous ammonium
acetate or cuprous ammonium formate

3. Hydrogen gas as by-product of petroleum refining operation

4. Electrolysis of water: H2O H2 + ½O2
 Reaction: N2 + 3H2 2NH3
Temperature requirement …………. 500oC
Pressure ………… 200 to 1000 atm
(2,940 to 14,700 psi)
Catalysts: a. finely divided iron
b. Al2O3

 The above process of ammonia manufacture is known as the

Haber process. An industrial process for the manufacture of
Ammonia from nitrogen gas and hydrogen gas.

Fritz Haber – a German scientist who discovered the above

process in 1913.
Interpretations of the reaction: N2 + 3H2 = 2NH3

1. Molecular interpretation
1 molecule N2 + 3 molecules H2 = 2 molecules of NH3

2. Molar interpretation
1 mol N2 + 3 mol H2 = 2 mol NH3

3. Mass interpretation
28.0 g N2 + (3x2.02 g H2) = 2x17.0g NH3

Stoichiometry: N2 + 3H2 = 2NH3

3 moles of H2 produce 2 moles of NH3
3 mol H2 approx = 2 mol NH3
 Nitrogen from, N2 Hydrogen, H2
liquid air from natural gas

Compressor

Reaction chamber
(Heat, pressure, catalyst

Return pump Cooling unit

Liquid NH3

Steps in Haber process

Source: Cotton et al. 1976. Chemistry An Investigative Approach
 Properties of Ammonia gas

Formula NH3
Weight % N 82
Molecular weight, g 17.03
Critical temperature, oC 132.4
Critical pressure, atm 111.5
Heat of vaporization (-33.3oC) 1,061 cal/g
Liquid density (0oC) 637.8 g/L
Vapor density (1 atm, 0oC) 0.7708 g/L
Boiling temperature (1 atm) -33.3oC
Freezing temperature (1 atm) -77.7oC
Gaseous NH3 is lighter than air, but on compression and cooling it becomes
Liquid about 60% as heavy as water.

Gaseous NH3 is extremely irritating to the eyes and respiratory system at con-
centration up to 0.07% by volume. At concentration of 0.17% causes convulsive
coughing, and at concentration of o.5% to 1% is rapidly fatal after short
exposure.
Comparative amount of N2 fixed by different systems
Industrial fixation (Haber process) 40M mt/yr
Biological N fixation (BNF) 175M mt/yr
Atmospheric fixation (lightning) 10M mt/yr
Source: FAO. 1983. Technical Handbook on Symbiotic Nitrogen Fixation
Legume-Rhizobium

Nitrogen fixation which reduces N2 to NH3 requires energy.

The Haber process uses non-renewable fossil fuel. In terms of energy
requirement for manufacturing, packing and distribution,
One ton of N fertilizer requires either 2000 kg of fuel oil or
5 tons of coal
 Conversion of NH3 to solid N fertilizer materials

a. Synthesis of ammonium sulfate

2NH3 + H2SO4 (NH4)2SO4

Characteristics: 1. White crystalline salt

2. Contains 21% N & 24 % S
3. Solubility in water
-at 0oC is 70.6 g/100g water
-at 100oC is 103.8 g/100g water
4. Has a physiological acidifying effect
The residual acidity effect on the soil
requires 5.3 lbs (2.3 kg) of lime per pound
(0.45 kg) of nitrogen.
 Conversion of NH3 to solid N fertilizer materials

b. Synthesis of urea

2NH3 + CO2  NH2COONH4

540 psi (340 atm) ammonium carbamate

NH2COONH4 CO(NH2)2 + H 2O

Ammonium carbamate is an intermediate product, it losses a molecule of

water and is converted to urea

Characteristics of urea
- white crystalline organic chemical
- it contains 45% to 46% N
- soluble in water up to 50% by weight of solution
and the solution is endothermic
c. Synthesis of ammonium chloride
NH3 + HCl NH4Cl

Contains 26% N and is acid forming

d. Synthesis of ammonium nitrate

NH3 + HNO3 NH4NO3

-The reaction is exothermic yielding about 23,000 calories

per mole of NH4NO3
-white granulated salt
-contains 33 to 34% N
 Reactions of Nitrogen Fertilizers
In Soils
A. Under aerobic soil conditions
What is an aerobic soil?
An aerobic soil is where oxidizing conditions
occur. This is usually an upland soil where crops
like corn, cassava, sugarcane etc. are grown.
1. Nitrification – refers to the transformation of ammonium
ions to nitrite and nitrate.

2NH4+ + 3O2 2NO2- + 4H+ + 2H2O + E

2NO2- + O2 2NO3- + E

Autotropic organisms involved:

Nitrosomonas sp.
Nitrobacter sp.
 2. Volatilization

NH4+ + OH- NH3 + H2O

This reaction occurs when ammonium containing fertilizers

are applied on soils with high pH values or soils that are newly
applied with lime.

B. Under paddy soil conditions

What is a paddy soil?
 saturated with water

 puddled state

 anaerobic

 usually grown to wetland rice

 reduced state (presence of reduced forms of

iron, manganese, nitrogen, carbon
 low redox potentials
Land preparation of paddy soil for rice using the
traditional method (carabao and comb tooth harrow)
Land preparation
 Redox Profile of a Paddy Soil Grown to Rice

Source: Sanchez, P. 1972.

 Denitrification

 2NO3- + 12H+ + 10e- N2 + 6 HOH

 can be prevented by applying the fertilizer in the

reduced zone of the paddy soil
 Management of N Fertilizers for Sustainable
Crop Production in Paddy Soils

Strategy: Increase the utilization efficiency of applied nitrogen

fertilizer by reducing gaseous losses

Technology: Deep placement of N fertilizer, ammonium containing

fertilizer should be applied in the reduced zone of the
paddy soil. Ammonium ions in the reduced zone of the
paddy soil is stable and available to the rice plant.
End of the slides
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