IGCSE Biology / Human influences on the environment

How fertilisers increase crop yield revision notes

Edexcel International GCSE Biology (4BI1), chapter 15: Human influences on the environment, specification point 5.3. Free lesson.

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Fertilisers replace mineral ions removed when crops are harvested, helping crops grow and increasing yield. Each mineral has a particular role, but excess fertiliser can pollute waterways.

Why harvesting removes minerals from soil

In a wild meadow, plants die where they grew, so their minerals return to the soil. In a field, the crop is harvested and taken away. The minerals in its tissues leave with it, so repeated harvests reduce the soil’s mineral supply. Crop roots absorb mineral ions from the soil through root hair cells, by active transport. Nitrate is lost fastest because plants need more of it than the other mineral ions described here. Less nitrate means fewer amino acids and less protein can be made. Growth falls, so the next yield (the amount of crop produced) is smaller.

What the main mineral ions are used for

Fertilisers replace mineral ions that crops need. Each ion has a different role, so link the ion to what it supplies and then to what happens to the plant if it is short. Nitrate supplies nitrogen for making amino acids. These are joined to make proteins, which are needed for new cells and growth. A shortage stunts growth and can yellow older leaves. Magnesium is needed to make chlorophyll, the green substance used in photosynthesis. A shortage causes yellow leaves because the plant cannot photosynthesise properly. Phosphate is needed for DNA, cell membranes and healthy root…

How nitrate fertiliser increases crop yield

When roots absorb more nitrate ions, the plant has more nitrogen available to build the substances needed for growth. This leads to taller plants and darker green leaves.

Why excess fertiliser can cause pollution

Adding fertiliser can replace minerals and support crop growth, but more is not always better. Once the crop cannot absorb the extra fertiliser, rain can wash the surplus into rivers and lakes. Excess fertiliser in waterways causes eutrophication.

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