Fertilisers

Crop field

As crops grow they remove nutrients, such as compounds of nitrogen, potassium and phosphorus, from the soil. These crops are harvested and taken away from the fields where they were grown. If this process is repeated for a number of years the supply of nutrients in the soil is exhausted. The land becomes less fertile, so plants grow poorly and produce only a small yield.

Farmers use fertilisers to put back into the soil the nutrients that have been removed by growing crops.

Different methods of farming

Farmers using intensive methods of agriculture use synthetic fertilisers. These contain nutrients that have been made in factories.

Farmers using organic methods use manure, which is the waste material from animals such as cows. Both synthetic fertilisers and manure contain the essential nutrients needed for crops to grow well.

Farmers using organic methods may also use crop rotation. In a field they grow a plant that puts nutrients into the soil, for example the leguminous plant, clover, then the next year they grow a crop that uses these nutrients. This cycle is repeated to ensure that the nutrients in the soil are not exhausted.

Pests and diseases

If crops are attacked by pests or diseases their yields are reduced.

Intensive farming

Spraying a crop of oil seed rape with insecticide

Farmers using intensive methods of agriculture combat pests and diseases by spraying their crops with chemicals that kill the pests or disease organisms. These chemicals are synthetic compounds produced by the chemical industry.

However, some of the chemicals used by these farmers may also kill helpful insects such as bees. Furthermore, the chemicals may get into water supplies or food chains, harming wildlife.

Organic farming

Farmers using organic methods use other ways to combat pests and diseases.

These include:

• spraying natural chemicals obtained from plants onto their crops
• picking pests such as caterpillars off the plants by hand
• placing natural predators of the pests onto the crops
• growing, amongst the crops, other plants that repel insect pests

The methods used in organic farming are likely to cause less damage to the environment than the synthetic chemicals used in intensive farming.

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