Learning outcomes
Students should understand
the following
 Why fertilisers are needed
in agricultural systems.
 How do natural and
artificial fertiliser differ
 How do fertiliser improve
productivity
Success criteria
Candidates should be able to:
 Analyse,
 Interpret
 Evaluate
data relating to use of fertilisers.
The need for fertilisers
Why do we need fertilisers?
 In natural ecosystems minerals are recycled back into
the soil.
 Agriculture tends to be concentrated on specific areas
of land that are used repeatedly
 Mineral ions that are absorbed by the crop are
removed.
 The level of mineral ions in the soil
will decrease.
 The urine, faeces and dead remains of
the consumer are rarely returned to
the same area of soil.
Productivity
Why do fertilisers increase productivity?
 Nitrogen is an essential element of proteins and DNA,
both of which are needed for growth.
 With extra nitrate available plants are likely to
 Develop earlier,
 Grow taller,
 Have greater leaf area
 This will increase the rate of photosynthesis and
improve productivity
Fertilisers
 The rate of plant growth in usually limited by the
availability of mineral ions in the soil.
 Adding more of these ions as fertiliser is a simple way
to improve yields.
 The key mineral ions that are added to the soil are
nitrate, phosphate and potassium ions (NPK).
Inorganic fertilisers
The most commonly used fertilisers are the soluble inorganic
fertilisers containing nitrate, phosphate and potassium
ions (NPK).
Inorganic fertilisers are very effective but also have
undesirable effects on the environment:
• Since nitrate and ammonium ions are
very soluble, they do not remain in the
soil for long and are quickly leached
out, ending up in local rivers and lakes
and causing eutrophication.
• They are also expensive.
Organic fertilisers
 Examples - animal manure, bone meal, composted
vegetable matter, crop residues, and sewage sludge.
 These contain the main elements found in inorganic
fertilisers (NPK), but in organic compounds such as
urea, cellulose, lipids and organic acids.
 Plants cannot make use of these organic materials in
the soil: their roots can only take up inorganic mineral
ions such as nitrate, phosphate and potassium.
 But the organic compounds can be digested by soil
organisms such as animals, fungi and bacteria, who
then release inorganic ions that the plants can use.
Organic fertilisers - Advantages
 They are less soluble than inorganic fertilisers, the
inorganic minerals are released more slowly as they are
decomposed. This prevents leaching and means they
last longer.
 The organic material improves soil structure by
binding soil particles together and provides food for
soil organisms such as earthworms. This improves
drainage and aeration.
 The organic wastes need to be disposed of anyway, so
they are cheap.
Organic fertilisers - Disadvantages
 They are bulky and less concentrated in minerals than
inorganic fertilisers, so more needs to be spread on a
field to have a similar effect.
 They may contain unwanted substances such as weed
seeds, fungal spores, heavy metals.
 They are also very smelly!
 Research suggests that a combination of both
Minerals should be added
in appropriate quantities as
there is a point at which
further increases in
quantity of fertilizer no
longer increases
productivity.
Yield of wheat/tonnes hectare-1
inorganic and organic fertilizers gives the greatest long
term productivity.
Mass of nitrogenous
fertiliser added /kg/hectare
A2 TEXTBOOK p99
Productivity using different forms of nitrogen fertiliser
60
Productivity ( fresh mass/tonnes hectare-1)
50
40
30
20
10
0
No added nitrogen Ammonium nitrate
Manure
Bone meal
Ammonium
sulphate
Urea
Which forms of nitrogen used in the investigation are natural fertilisers?
Productivity using different forms of nitrogen fertiliser
60
Productivity ( fresh mass/tonnes hectare-1)
50
40
30
20
10
0
No added nitrogen Ammonium nitrate
Manure
Bone meal
Ammonium
sulphate
Urea
Why did the investigation include a plot with no nitrogen fertiliser added?
Productivity using different forms of nitrogen fertiliser
60
Productivity ( fresh mass/tonnes hectare-1)
50
40
30
20
10
0
No added nitrogen Ammonium nitrate
Manure
Bone meal
Ammonium
sulphate
Urea
Suggest how the addition of nitrogen fertiliser, in whatever for, increased
productivity.
Productivity using different forms of nitrogen fertiliser
60
Productivity ( fresh mass/tonnes hectare-1)
50
40
30
20
10
0
No added nitrogen Ammonium nitrate
Manure
Bone meal
Ammonium
sulphate
Urea
The mass of each fertiliser used was different in each case. Suggest why this was
necessary.
Productivity using different forms of nitrogen fertiliser
60
Productivity ( fresh mass/tonnes hectare-1)
50
40
30
20
10
0
No added nitrogen Ammonium nitrate
Manure
Bone meal
Ammonium
sulphate
Urea
It is sometimes claimed that nitrogen fertilisers in the form of ammonium salts increase
productivity of crops better than other forms of nitrogen fertilisers. State, with your
reasons, whether or not you think the results of this experiment support this view.
Productivity using different forms of nitrogen fertiliser
60
Productivity ( fresh mass/tonnes hectare-1)
50
40
30
20
10
0
No added nitrogen Ammonium nitrate
Manure
Bone meal
Ammonium
sulphate
Urea
The increase in productivity when manure was applied was lower than other forms of
nitrogen fertiliser. This is because the manure has to break down before its nitrogen is
released and this process takes a few months. How might a farmer who spreads manure
on his crops, use this information in order to improve productivity?
Exam question
(a) (i)Describe one way in which mineral ions are released from rocks into soil.
(1)
(ii)Describe how detritivores are involved in the recycling of nutrients.
(3)
(b)The bar chart shows the amounts of nitrate and phosphate in soil from two different
areas of grassland, A and B. Both areas are used for grazing.
7
Area A
No fertiliser or
manure added.
Contains:
2 species of grass
10 other species of
flowering plant
Area B
Sprayed yearly with
liquid manure.
Contains:
3 species of grass
1 other species of
flowering plant
6
Amount of
nitrate and
phosphate in
soil/kg per
hectare
nitrate
5
phosphate
4
3
2
1
0
Area A
Area B
Grassland area
(i) Explain the effect of nitrate and phosphate supply on the diversity of plants.
(2)
(ii)Area B is going to become part of a nature reserve. A proposed change in land
management is to stop spraying with liquid manure. Explain the likely effect of this
change on the diversity of plants.
(1)
(Total 7 marks)
(a) (i)
named factor and it action;
( rain water/erosion washes ions from rocks, temperature increases
solubility, oxidation forms salts)
1
(ii) (larger detritivores/named example) break up larger pieces (by feeding);
excrete nitrogenous wastes/faeces/droppings;
increases surface area available to bacteria/microorganisms/fungi/
decomposers;
decomposition by microorganisms releases minerals/nutrients to soil;
any
3
(b) (i) grasses able to grow faster/more/better outcompete flowering plants
in higher nutrient supply;
(higher nutrient) reduces diversity;
2
(ii) reduced level of minerals/nutrients enables flowering plants to compete
more effectively for nitrate/phosphate/ nutrient;
1
[7]
Learning outcomes
Students should understand
the following
 Why fertilisers are needed
in agricultural systems.
 How do natural and
artificial fertiliser differ
 How do fertiliser improve
productivity
Success criteria
Candidates should be able to:
 Analyse,
 Interpret
 Evaluate
data relating to use of fertilisers.