9. FERTILIZER

9. FERTILIZER

A fertilizer is a chemical substance which contains plant food. Plants take many different foods from the soil. But they often need more nitrogen, phosphorus and potassium than it supplies. So these substances are given in fertilizers.

Some fertilizers are prepared from natural substances found in the Earth’s surface and mined for this purpose. Some are made in fertilizer factories and some are the waste products, or by-products, of the manufacture of other articles.

Although plants need nitrogen, they do not take it from the soil as pure nitrogen. They take nitrogen compounds, that is, nitrogen combined with other substances. Therefore, all nitrogenous fertilizers are compounds, such as calcium nitrate, nitrate of soda, etc. Nitrate of soda comes from great mines in Chile, South America, and other countries. Sulphate of ammonia is the most widely used of these fertilizers. Different amounts of these nitrogenous fertilizers are applied to different crops.

Phosphorus is also taken in as a compound. The most common phosphatic fertilizer is superphosphate. It is prepared from the calcium phosphate that is mined in the USSR, North Africa and the United States.

Another phosphatic fertilizer comes from the manufacture of steel. It is called basic slag.

Potassium, the third important material for fertilizer, is mined in many parts of the Soviet Union.