Water and mineral salts enter the plant mainly through the roots from the soil. This process is called mineral nutrition. In this process, the root hairs in the suction zone play an especially important role. This is why soil nutrition is also called root nutrition. Root nutrition provides the plant with water and mineral salts.
The plant is able to regulate the intake of mineral substances: only those substances that are necessary for the plant during a given period of life can penetrate through the cells of the inner layer of the root bark.
Most of all, the plant needs nitrogen, potassium and phosphorus. If the plant does not receive at least one of the necessary substances, then its vital processes are sharply disrupted.
For example, it was found that with a lack of nitrogen, plant growth is inhibited and small leaves are formed. Lack of potassium slows down the processes of cell division and elongation, and causes death of the root tip. Lack of phosphorus slows down the metabolism.
The rest of the minerals are required in small quantities, but are also important for the plant.
For example, with a lack of magnesium, the formation of chloroplasts and chlorophyll is disrupted. Lack of sulfur reduces photosynthesis.
An excess of other substances does not replace the missing ones. This is because nutrients have different functions in plants. For example, it was found that substances containing nitrogen promote the growth of plants containing phosphorus – the early ripening of fruits, and those containing potassium – the fastest outflow of organic matter from the leaves to the roots.