Nitrates are vital for plant growth, entering soil through the decomposition of organic matter and undergoing processes like ammonification and nitrification by specific bacteria. The use of nitrate fertilizers significantly benefits plant growth, particularly for legumes like peas due to mutualistic bacteria. However, excessive fertilization can lead to water pollution and ecological issues, emphasizing the need for sustainable farming practices.

3. Nitrates are essential for plant growth
Root
uptake
Nitrate
NO3
-
Plant
protein

4. Nitrates are recycled via microbes
Nitrification
Nitrification
Ammonium NH4
+
Ammonification
Nitrite NO2
-
Soil organic nitrogen
Animal
protein
Root
uptake
Nitrate
NO3
-
Plant
protein

5. -
ANIMAL PROTEIN
PLANT
PROTEIN
SOIL ORGANIC NITROGEN
AMMONIFICATIONAMMONIA NH4
+
NITRIFICATION
NITRITE NO2
-
NITRIFICATION
NITRATE NO3
-

6.  Nitrogen enters the soil through the
decomposition of protein in dead organic
matter
 Amino acids + 11/2O2  CO2 + H2O + NH3 +
736kJ
 This process liberates a lot of energy
which can be used by the saprotrophic
microbes

7.  This involves two oxidation processes
 The ammonia produced by ammonification is an energy
rich substrate for Nitrosomas bacteria
 They oxidise it to nitrite:
NH3 + 11/2O2  NO2
- + H2O + 276kJ
 This in turn provides a substrate for Nitrobacter
bacteria oxidise the nitrite to nitrate:
 NO3
- + 1/2O2  NO3
- + 73 kJ
 This energy is the only source of energy for these
prokaryotes
 They are chemoautotrophs

9.  Electrical storms
 Lightning provides sufficient energy to
split the nitrogen atoms of nitrogen gas,
 Forming oxides of nitrogen NO3 and
NO2

10. Treatments Yield / g
Oats Peas
No nitrate & sterile soil 0.6 0.8
Nitrate added & sterile soil 12.0 12.9
No nitrate & non-sterile soil 0.7 16.4
Nitrate added & non-sterile soil 11.6 15.3

11. 0
2
4
6
8
10
12
14
16
18
N.N.&S N.A.&S N.N.%N.S. N.A.&N.S.
OATS
PEAS

12.  Adding nitrate fertiliser clearly helps the growth of both
plants
 The presence of microbes permits the peas to grow
much better than the oats
 The peas grow better in the presence of the microbes
than they do with nitrate fertiliser added
 The difference is due to the present of mutualistic
nitrogen fixing bacteria which live in the pea roots.

13.  The Haber-Bosch Process
N2 + 3H2  2NH3 - 92kJ
 The Haber process uses an iron catalyst
 High temperatures (500°C)
 High pressures (250 atmospheres)
 The energy require comes from burning
fossil fuels (coal, gas or oil)
 Hydrogen is produced from natural gas
(methane) or other hydrocarbon

14. This involves two oxidation processes
The ammonia produced by ammonification
is an energy rich substrate for Nitrosomas
bacteria
They oxidise it to nitrite:
NH3 + 11/2O2  NO2
- + H2O
+ 276kJ
This in turn provides a substrate for
Nitrobacter bacteria oxidise the nitrite to
nitrate:
NO3
- + 1/2O2  NO3
-
+ 73 kJ
This energy is the only source of energy
for these prokaryotes
They are chemoautotrophs
Out
gassing

16. University of Sydney

18.  Cyanobacteria are nitrogen fixers that also
fix carbon (these are photosynthetic)
 Rhizobium bacteria are mutualistic with
certain plant species e.g. Legumes
 They grow in root nodules
 Azotobacter are bacteria associated with
the rooting zone (the rhizosphere) of plants
in grasslands

19. Ammonium
NH4
+

20. Sources of fixed nitrogen Production / M tonnes a-1
Biological 175
Industrial 50
Internal Combustion 20
Atmospheric 10

21.  Nutrient enrichment of water bodies
 Nitrates and ammonia are very soluble in
water
 They are easily washed (leached) from free
draining soils
 These soils tend to be deficient in nitrogen
 When fertiliser is added to these soils it too
will be washed out into water bodies
 There algae benefit from the extra nitrogen
 This leads to a serious form of water
pollution

22. FertilisersSewage or
other organic
waste
Fertilisers washed into river or lake

23. Increased Biochemical
Oxygen Demand (BOD)
Hot water
from industry
(Thermal
pollution)
Pollution
from oil or
detergents
Reduction in dissolved O2
Making things worse!

24. The death of a lake
Death/emigration
of freshwater
fauna
Increased nitrite
levels
NO3
-  NO2
-
Reduction in dissolved O2

25.  Food production relies heavily upon synthetic
fertilisers made by consuming a lot of fossil
energy
 Food will become more expensive to produce
 Nitrogen fixing microbes, using an enzyme
system, do the same process at standard
temperatures and pressures essentially using
solar energy
 Answer: Genetically engineered biological
nitrogen fixation

26. future

28. Sediments 10 Gt
Nitrification
Root
uptake
Biological
fixation
Nitrification
Ammonium NH4
+
Ammonification
Nitrite NO2
-
Dissolved in water
6000 Gt
Denitrification
Leaching
Nitrate
NO3
-
Soil organic nitrogen
9500 Gt
Atmospheric
fixation
Out
gassin
g Industrial
fixation
Plant protein
3500 Gt
Animal
protein
Atmospheric Nitrogen
4 000 000 000 Gt
© 2008 Paul Billiet ODWS