6.4 - Uses of natural and artificial fertilisers

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6.4 - Uses of natural and artificial fertilisers
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• Learning outcomes

• Success criteria

• Candidates should be able to
• Analyse,
• Interpret
• Evaluate
• data relating to use of fertilisers.

• Students should understand the following
• Why fertilisers are needed in agricultural
  systems.
• How do natural and artificial fertiliser differ
• How do fertiliser improve productivity

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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.

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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

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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).

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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.

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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.

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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.

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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!

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• Research suggests that a combination of both
  inorganic and organic fertilizers gives the
  greatest long term productivity.

Minerals should be added in appropriate
quantities as there is a point at which further
increases in quantity of fertilizer no longer
increases productivity.
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A2 TEXTBOOK p99
Which forms of nitrogen used in the investigation
are natural fertilisers?
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Why did the investigation include a plot with no
nitrogen fertiliser added?
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Suggest how the addition of nitrogen fertiliser,
in whatever for, increased productivity.
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The mass of each fertiliser used was different in
each case. Suggest why this was necessary.
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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.
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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?
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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.
• (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)

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• (i) named factor and it action( rain
  water/erosion washes ions from rocks, temperature
  increasessolubility, 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 plantsin higher nutrient
  supply
• (higher nutrient) reduces diversity 2
• (ii) reduced level of minerals/nutrients enables
  flowering plants to competemore effectively for
  nitrate/phosphate/ nutrient 1
• 7

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• Learning outcomes

• Success criteria

• Candidates should be able to
• Analyse,
• Interpret
• Evaluate
• data relating to use of fertilisers.

• Students should understand the following
• Why fertilisers are needed in agricultural
  systems.
• How do natural and artificial fertiliser differ
• How do fertiliser improve productivity