Fertilisers

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Plants require chemical nutrients from the soil in order to have healthy growth. Three of the elements found in essential nutrient compounds are:

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nitrogen (N)

phosphorus (P)

potassium (K)

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Sources of fertilisers

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Natural fertilisers:

Decay of dead plants and animals

Decay of plant and animal waste

Synthetic fertilisers:

Haber process-making ammonia from nitrogen and hydrogen

Ostwald process-oxidising ammonia to make nitric acid

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proplems

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Unfortunately soluble fertilisers can be washed away by rainwater into rivers and lakes.

This causes pollution resulting in fish dying and algal blooms (a green coating) covering water.

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The Haber Process

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Central to the production of fertilisers containing nitrogen, is a supply of ammonia (NH3) which is an essential starting point for the production of fertilisers.

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Nitrogen + hydrogen = ammonia

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N2(g) + 3H2(g)=2NH3(l))

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Table

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Condition: Temperature

Reason: Moderate/Low temperature – reaction too slow: High temperature – ammonia decomposes.

condition: Pressure

Reason: High - This increases the yield of ammonia.

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Nitrate fertilisers

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There are many useful synthetic fertilisers containing nitrogen, phosphorus and potassium.

Different crops need fertilisers with different proportions of nitrogen, phosphorus and potassium.

If you go to buy a fertiliser from a shop, you often find that the fertiliser is classified according to which plant it can improve the best.

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Percentage composition of fertilisers

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As with metal ores, it is useful to be able to calculate exactly what proportion the essential nutrients accounts for in a fertiliser.