Friday, 24 September 2021 08:46


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The fertiliser industry

The need for fertilisers is increasing due to:

  • the growth in the world population – more people means more food is necessary and
  • the decrease in available agricultural land – less land means the available land must produce a lot of high quality food at a high rate (fast).

Nutrients in the soil are used by the plants that grow and these nutrients must be replaced.
Inorganic fertilisers are produced industrially in the Haber, Contact & Ostwald processes at chemical plants like SASOL.

7.1 Nutrients required by plants


Primary non- mineral nutrients

Primary mineral nutrients

Secondary nutrients  Trace elements
  • C carbon
  • H hydrogen
  • O oxygen
  •  N nitrogen
  • P phosphorus
  • K potassium
  • Ca calcium
  • Mg magnesium
  • S sulphur
  • Cu copper
  • Fe iron
  • Mn manganese
  • Zn zinc
  • I iodine
  • From the air  as CO2(g) and 
  • in rainwater as H2O(ℓ)
  • Absorbed from the soil
  • as water- soluble salts.
  • by the roots
  • Absorbed from the soil
  • as water-soluble salts.
  • by the roots
  •  Absorbed from the soil
  • as water-soluble salts.
  • by the roots
  • Sufficient available in the air
  • Used up and must be replaced by using fertilisers
  • Sufficient available in the soil
  • Sufficient available in the soil


  • Promote: to help or encourage
  • Essential: absolutely necessary
  • Inorganic: not produced by a living organism; not containing carbon
  • Mineral: an inorganic solid substance that occurs naturally (not man-made)
  • Inert: unreactive
  • Sufficient: enough

Did you know?

  • Bone meal is produced when the bones of dead animals are ground into powder.
  • Kelp meal is dried seaweed.
  • Granite meal is finely ground granite rock.

Activity 1

  1. Which of the following is a primary mineral nutrient that is needed by plants?
    1. N
    2. C
    3. Mg
    4. Na (2)  [2]

1. A  [2]

7.2 Functions and sources of the primary mineral nutrients

 Nutrient  (N)  Phosphorous (P)  Potassium (K)
  •  Promotes growth of leaves;
  • gives a healthy green colour to the plant;
  • is part of chlorophyll which is needed for photosynthesis.
    7.2 1 hghahd
  • Promotes development of roots and stems;
  • is essential for good growth;
  • is necessary for photosynthesis;
  • is active during production of oils, sugar and starch.
    7.2 2 khjyagduya
  •  Ensures high quality and  colourful flowers, fruit and vegetables;
  • promotes resistance against diseases.
    7.2 3 kjhbjuhyaguygd
Sources Pre- World War II
  •  Guano
    (Sea bird excrement)
  • Plant Compost
  •  Bone meal
  •  Wood ash
  • Mined in Germany
  •  Animal manure
  • Fish emulsion
  • Guano (bat excrement)
  • Dried animal blood
  • Compost
  •  Bone meal
  •  Kelp meal
    (ground seaweed)
  •  Nitrate (NO3−) salts and
  • ammonium (NH4+) salts
  • from ammonia (NH3) produced in the Haber process
  • E.g.
    • NH4NO3 ammonium nitrate
    • KNO3 potassium nitrate
    • (NH4)2SO4 ammonium sulphate
  •  Superphosphates
  • CaH4(PO4)2·H2O
  • Monoammonium phosphate (MAP) NH4H2PO4
  • Diammonium phosphate (DAP):
  •  KCℓ, potassium chloride
  • is imported to South Africa.
  • Also:
    • KNO3 potassium nitrate
    • K2SO4 potassium sulphate

Atmospheric nitrogen is fixed into compounds containing nitrates (NO3−) or ammonium ions (NH4+) so that the nitrogen can be taken in by plants and used as nutrient.

  • Atmospheric fixation: fixation by lightning;
  • Biological fixation: fixation by bacteria in the ground and by the roots of legumes;
  • Industrial fixation: fixation by industrial processes like the Haber process.


  • “Fixed” means “attached”.

industrial production of kjhjyagd

  1. In the Haber process:
    Steam reforming of methane (natural gas) in the presence of a platinum catalyst to form a mixture of carbon monoxide (CO) and hydrogen (H2) gases (synthesis gas).
    haber process jhygjygad
  2. In the Contact process:
    2.1 If SO2(g) is not dried before step 2, it reacts with water to form sulphurous acid, H2SO3(aq) which forms acid rain, a type of rain which is produced as a side-effect of human industrial activities, which is corrosive to structures and harmful to living things.
    SO2(g) + H2O(ℓ) → H2SO3(aq)
    2.2 SO3(g) reacts with water to form gaseous sulphuric acid, H2SO4(g) which escapes into the atmosphere and forms acid rain.
    SO3(g) + H2O(ℓ) → H2SO4(g)
  3. In the Contact process:
    3.1 The 1st step is known as the catalytic oxidation of ammonia.
    4NH3(g) + 5O2(ℓ) → 4NO(g) + 6H2O(g)
    3.2 NO2 (nitrogen dioxide) is a brown gas which reacts with water to form HNO3(g) which escapes into the atmosphere and forms acid rain.

Fluorapatite, Ca5(PO4)3F

  1. is mined at Phalaborwa;
  2. is insoluble in water and can’t be absorbed by plant roots;
  3. reacts with sulphuric acid, H2SO4(ℓ) to produce phosphoric acid, H3PO4(aq).


  1. is produced when fluorapatite reacts with sulphuric acid H2SO4 and is a mixture of Ca(H2PO4)2·H2O and CaSO4 (gypsum)

Triple Superphosphate

  1. is produced when fluorapatite reacts with phosphoric acid H3PO4 to form Ca(H2PO4)2·H2O (no CaSO4 is formed).

7.3 The industrial production of fertilisers


Ammonium sulphate

Ammonium nitrate


Monoammonium phosphate (MAP)
Diammonium phosphate (DAP)



Ca(H2PO4)2·H2O +  CaSO4
Triple Superphosphate



(Haber process)

Sulphuric acid
(Contact process)


(Haber process)

Nitric acid
(Ostwald process)


(Haber process)

Phosphoric acid



sulphuric acid
(Contact process)
Phosphoric acid


(Haber process)

Carbon dioxide
(by-product of the
Haber process)

Reaction equation  2NH3(g) + H2SO4(ℓ) →


 NH3(g) + HNO3(aq)

→ NH4NO3(aq)

 NH3(g) + H3PO4(aq) → NH4H2PO4(aq) 2NH3(g) + H3PO4(aq) →


 Not required  2NH3(g) + CO2(g) →
(NH2)2CO(g) + H2O(g)
  • Very soluble in  water;
  • easily absorbed by plant roots;
  • provides plants with both nitrogen (N) and sulphur (S).
  •  Very soluble in  water;
  • easily absorbed by plant roots;
  • provides plants with nitrogen (N).
  •  Very soluble in water;
  • easily absorbed by plant roots;
  • provides plants with both nitrogen (N) and phosphorous (P).
  • Soluble in water;
  • superphosphate also supplies the secondary nutrient S, sulphur;
  • widely used.
  • Very soluble in  water;
  • easily absorbed by plant roots;
  • provides plants with nitrogen (N).

7.4  Flowchart: The industrial production of fertilisers

7.4 kuhiykaguyda

e.g. Worked example 1
Study the diagram below that illustrates the industrial preparation of nitric acid and answer the questions that follow.
worked example 1 kuhguyagd

  1. 1.1 Write down a balanced chemical equation for the formation of product A.
    1.2 Name the catalyst used during the reaction in Question 2.1.
    1.3 What name is given to the reaction in Question 2.1? Give a reason for this name.
    1.4 Write down a balanced chemical equation for the formation of product B.
    1.5 Name the products A and B.
    1.6 Write down a balanced chemical equation for the formation of product C.
    1.7 Name product C.
  2. Ammonium nitrate is important for its use in fertilisers and explosives. It can be prepared by the reaction of nitric acid and ammonia.
    2.1 Write down a balanced equation for the preparation of ammonium nitrate.
    2.2 What kind of fertiliser is ammonium nitrate?
    2.3 Which characteristic of ammonium nitrate makes it suitable for use as a fertiliser?
    2.4 Which characteristic of ammonium nitrate makes it suitable to be used in explosives?
  3. Ammonium sulphate is often used as a fertiliser to supplement nitrogen and sulphur shortages in plants.
    3.1 Compile a flow chart that indicates all the industrial steps for the preparation of ammonium sulphate from air, natural gas and sulphur.
    3.2 Give balanced equations for all the reactions that take place during the preparation of ammonium sulphate from air, methane and sulphur.


  1. 1.1                         Pt
    4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g)
    1.2 Platinum or Rhodium
    1.3 Catalytic oxidation of ammonia
    1.4 2NO(g) + O2(g) → 2NO2(g)
    1.5 A: Nitrogen monoxide B: Nitrogen dioxide
    1.6 3NO2(g) + H2O(ℓ) → 2HNO3(aq) + NO(g)
    1.7 Nitric Acid
  2. 2.1 HNO3 + NH3 → NH4NO3
    2.2 Primary mineral nutrient
    2.3 High nitrogen content per mass
    2.4 Nitrogen bonds are easily broken and therefore it decomposes rapidly and easily (explodes).
  3. Answers for 3.1 and 3.2
    • O2 + N2 (air)
    • CH4 (methane)
    • S
    • To produce: (NH4)2SO4 (ammonium sulphate)

steps khugjygugd

7.5 N:P:K fertilisers

As plants need a large amount of the primary mineral nutrients (nitrogen, phosphorus and potassium) and these need to be replenished (replaced) in the soil to make sure that crops grow well to provide enough food, NPK fertilisers that contain a mix of these nutrients, are usually used. They are produced by mixing a nitrogen fertiliser, a phosphorus fertiliser and potassium chloride (KCℓ).
7.5 kuhguyagygd

Step by step
Step 1. Find the mass of the bag.
Step 2. Find the percentage (%) of fertiliser in the bag (the number in brackets).

  • 26% fertiliser in bag
    ∴ 74% inert compounds

Step 3. Find the mass of fertiliser in the bag.

  • mass of fertiliser = percentage fertiliser  × mass of bag
    = 26 × 10Kg = 2,6 Kg

Step 4. Find the total number of parts of nutrients in the bag. (Add the numbers representing the ratios of each of the elements, N, P and K.)
7.5 2 khuguayguydg
Step 5. For each element (N, P and K) find the percentage of the element in the fertiliser:

Related Items

  • % element = ratio element × % fertiliser   
  • %N=    ratio N      ×% fertiliser = 3 × 26 = 8,67
              total ratio                          9
  • %P=     ratio P      ×% fertiliser = 1 × 26 = 2,89
              total ratio                           9
  • %P=     ratio K     ×% fertiliser = 5 × 26 = 14,44
              total ratio                          9

Step 6. For each element (N, P and K) find the mass of that element in the bag.

  • mass element = ratio element × % fertiliser × mass of bag
                                  total ratio              100   
    • 3  × 26   × 10 kg = 0,87 kg
      9    100
    • 1 ×  26   × 10 kg = 0,29 kg
      9    100
    • 5 × 26   × 10 kg = 1,44 kg
      9    100

The per component totals (0,87; 0,29; 1,44) add up to 2.6kg.

e.g. Worked example 2
A bag of fertiliser has the following information on it: 3 : 2 : 3 (26).

  1. What information can you deduce from these numbers?
  2. Calculate the percentage composition of the fertiliser in the bag.


  1. It shows the ratio N : P : K.
    3 + 2 + 3 = 8therefore the fertiliser mixture consists of:
    3/8 parts N; 2/8 parts P and 3/8 parts K
    These nutrients make up 26% of the mass of the bag content. The other 74% is made up of gypsum, lime and sand.
  2.  %N=     ratio N     ×% fertiliser
               total ratio
    • =3 × 26 = 9,75
    • = 2 × 26 = 6,5
    • = 3 × 26 = 9,75

7.6 Excessive use of fertiliser and the environment

The correct application of fertiliser to crops is essential for high quality, fast growing crops but using too much or unnecessary fertiliser has a negative effect on the environment.

  • Groundwater is contaminated by fertiliser leaching (spreading by water) into the ground.
  • Soil becomes acidic (pH decreases). Many plants do not grow in acidic soil.
  • Invasive plants grow excessively while indigenous plants die. Invasive plants are undesirable non-indigenous (foreign) plants that grow too fast and out-compete local plants.
  • Fertiliser in dams and rivers leads to “eutrophication”, defined below.
  • High nitrate concentrations in drinking water decreases the ability of haemoglobin in the blood to carry oxygen and leads to ‘blue baby syndrome’.

7.6.1 Eutrophication

  In water (dams and rivers)  On land 
  •  Poor (bad) control of waste products.
  • Excessive / unnecessary application of fertilisers.
  • Waste products (urine and faeces) and
  • excessive fertiliser nutrients
  • leach into ground water and
  • run into rivers and dams.
  • Poor (bad) farming practises:
  • Excessive / unnecessary use of fertilisers
  • Animal waste in feeding and milking stalls contains urea and ammonia and leaches into ground water.
  • Excessive growth of algae;
  • Algae die;
  • Bacteria feed on the algae and use oxygen;
  • Oxygen levels in the water drop;
  • Fish and other living organisms die.
  •  Invasive plants grow excessively, indigenous plants die;
  • Bird and insect species move away disturbing the ecosystems;
  • Soil erosion increases due to absence of indigenous plants with strong root systems.
Possible solutions
  • Strict control over all waste and sewage must be enforced.
  • Waste products:
  • must be treated and
  • not allowed to leach into groundwater or
  • run into rivers and dams.
  • Test soil to determine need for fertiliser – apply correct amount and type; prevent inflow of contaminated
  • Plant indigenous plants along rivers to prevent erosion and water; break down excess nitrogen
  • Conserve natural swamps which nutrients naturally;
  • Control animal waste in feeding and milking stalls.

An overabundance (excess, too much) of nutrients (N and P) in water leads to:

  • the fast and excessive growth of algae and other water plants (this is called ‘algal bloom’) and bacteria
  • causing a drop in the oxygen concentration in the water and
  • the death of fish and other living organisms in the water.


  • Overabundance / excess: more than is needed
  • Shortage: not enough
  • Invasive plants: plants that do not naturally grow in a certain area
  • Indigenous plants: plants that grow naturally in (are native to) a certain area
  • Swamps: ground that is uncultivated but is usually covered with water
  • Erosion: soil and rock is removed from the Earth’s surface by wind, rain or water
  • Stunted growth: reduced growth leading to smaller, underdeveloped plants

Activity 2

  1. Which ONE of the following is NOT associated with eutrophication in water?
    1. Dead zones
    2. Algal bloom
    3. Depletion of oxygen
    4. Increased aquatic life (2)  [2]


  1. D [2]

7.6.2 The effect of a shortage or excess of the primary nutrients (N, P and K) on plants

  N (nitrogen)  P (phosphorus)  K (potassium)
  • Little growth
  • Weak stems
  • Yellow leaves
  • Stunted growth
  • Slow growth
  • Purple leaves
  • Poor quality flowers and fruit (colour and taste)
  • Leaves have brown or yellow edges
  • Dark green leaves
  • Poor production of seed and fruit
  • Causes shortage of micro nutrients Fe and Zn
  • Causes shortage of micro nutrients Mg and Ca
  • Stunted growth
  • Poor quality flowers and fruit

7.7 Alternatives to inorganic fertilisers

Although fertilisers are essential for the fast growth of high quality crops, the negative effects of inorganic compounds on the environment must be taken into account. Alternative sources of organic nutrients that can be used to ensure good crops are:

  • Bone meal;
  • Animal manure;
  • Natural plant compost;
  • Bat guano (faeces);
  • Fish emulsions;
  • Kelp meal

Advantages of organic fertilisers:

  • Break down and release nutrients more slowly than inorganic fertilisers, so there is less chance of the fertiliser leaching into the soil and causing contamination of groundwater;
  • Usually cost less and
  • Are often available for free.

Disadvantages of organic fertilisers:

  • Not enough is available for large scale usage;
  • Provide less nutrients – more has to be used;
  • Slow release of nutrients sometimes harms plants;
  • Slow release may cause nutrients to be available too late in the plant’s growth cycle. 

Activity 3

Fertilisers allow farmers to grow crops in the same soil year after year. However, environmental problems, such as eutrophication, are associated with the application of fertilisers.

  1. State ONE PRECAUTION that a maize farmer can take to prevent eutrophication. (1)
    Nitric acid is an important reactant in the production of ammonium nitrate, a nitrogen-based fertiliser.
  2. Write down the name of the industrial process for the production of nitric acid. (1)
  3. Write down a balanced equation for the preparation of ammonium nitrate from nitric acid. (3)  [5]


  1. Use fertilisers sparingly  / Do not over-fertilise
    Make use of precision (computerised) application of fertilisers
    Ensure that water from fields does not run into rivers/dams
    Redirect water from fields into reservoirs/away from rivers/dams  (any one) (1)
  2. Ostwald process  (1)
  3. HNO3  + NH3 → NH4NO3  (3)  [5]

Activity 4

The rapidly increasing human population is resulting in an ever-increasing demand for food. To meet this demand, farmers apply fertiliser to the same cultivated land EACH YEAR.

  1. Explain why farmers have to apply fertilisers to their land each year. (1)
  2. Write down one negative impact that over-fertilisation can have on humans. (1)
  3. Sulphuric acid is an important substance used in the manufacture of fertilisers.
    The equation below represents one of the steps in the industrial preparation of sulphuric acid.
    2SO2(g) + O2(g) ⇋ 2SO3(g) ∆H<0
    3.1 Write down the name of the process used to prepare sulphuric acid in industry (1)
    3.2 Write down the name or the formula if the catalyst used in 2.3.1 (1)
    3.3 Is the forward reaction endothermic or exothermic? Give a reason for your answer. (1)
    3.4 Write down the name or formula of the fertiliser formed when sulphuric acid reacts with ammonia. (2)  [7]


  1. Fertilisers replenish nutrients depleted by the growing of crops  (1)
  2. Damage to crops/soil  resulting in small or no harvest/ less income. Excessive fertiliser seeps into groundwater and contaminates drinking water  or runs into rivers and/or dams and causes eutrophication  which may result in less income /famine/starvation /poor quality drinking water /fewer recreation areas/ environmental damage/ death of wild animals  (any one) (1)
  3. 3.1 Contact process  (1)
    3.2 V2O5  vanadium pentoxide  (any one) (1)
    3.3 Exothermic as∆H < 0  (1)
    3.4 (NH4)2SO4  OR / Ammonium  sulphate  (2) [7]

Activity 5

Ammonia, ammonium nitrate and ammonium sulphate are three important nitrogen-containing fertilisers. The flow diagram below shows how these fertilisers are produced in industry.
activity 5 uyguygayugd

  1. Use the information in the flow diagram above and write down the following:
    1.1 Name Process 1 (1)
    1.2 Balanced equation for Process 2 (3)
    1.3 Name or Formula for compound X (1)
    1.4 Balanced equation for the preparation of ammonium sulphate using sulphuric acid and compound Y (3)
    1.5 Name or Symbol of the primary nutrient in ammonium sulphate (1)
  2. Write down one positive impact of fertilisers on humans (1)
  3. Write down two negative impacts of the use of ammonium nitrate as fertiliser, on humans. (2)  [12]


  1. 1.1 Fractional distillation of liquid air  (1)
    1.2 N2 + 3H2 → 2NH3 (reactants  products  balance  (3)
    1.3 Nitric acid / HNO3  (1)
    1.4 H2SO4 + 2NH3 → (NH4)2SO4 (reactants  products  balance (3)
    1.5 Nitrogen / N  (1)
  2. Enhance growth of crops/plants  to produce more food for humans  food security for humans  production / application of fertiliser  results in job creation selling of fertilisers  stimulates the economy  (any one) (1)
  3. (Excessive) nitrates in water (eutrophication)  can result in blue baby syndrome or cancer  (Excessive) nitrates/ammonium ions in water can result in poor quality drinking water  or death of fish  or less food  or fewer recreational facilities  or famine due to killing plants / crops from the excess  or excessively changing the pH of the soil and thereby reducing the food production (any two) (2) [12]
Last modified on Wednesday, 29 September 2021 12:32