FertilisersCambridge IGCSE Chemistry: Revision notes

Fertilisers are chemicals added to soil to replace nutrients used up by growing plants.

Ammonium salts and nitrates are used as fertilisers. These compounds supply nitrogen in a form that plant roots can absorb from the soil.

NPK fertilisers are formulated to provide three key elements plants need for healthy growth:

• N — nitrogen
• P — phosphorus
• K — potassium

Providing all three together in the correct balance leads to improved plant growth, since each element supports a different aspect of plant development (e.g. nitrogen for leaf/stem growth, phosphorus for root development, potassium for flowering and disease resistance).

Fertilisers are not always fully absorbed by plants. Excess fertiliser can run off fields into rivers and lakes, meaning that water from natural sources may contain nitrates from fertilisers and phosphates from fertilisers and detergents, alongside other contaminants such as dissolved oxygen, metal compounds, plastics, sewage and harmful microbes.

This contamination links fertiliser use directly to water quality problems downstream.

Substances such as nitrates and phosphates from fertilisers can have both beneficial and potentially harmful effects once in water:

• Beneficial (in soil): provide nutrients that improve crop growth and yield
• Harmful (in water): excess nitrates and phosphates cause eutrophication — they over-fertilise algae and water plants, leading to excessive growth, oxygen depletion as they decompose, and the death of aquatic organisms such as fish