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Phosphorous shortage, how to recognize a phosphorus deficiency in plants

Posted on June 14 2019

Phosphorous shortage, how to recognize a phosphorus deficiency in plants


Phosphorus is an essential element for everything that lives. It plays a key role in metabolism and is a building block of cell walls, DNA and stimulates the root growth of the plant.

Often one speaks of a phosphorus deficiency in plants, but it is better to speak of a phosphate deficiency, since phosphorus in nature only occurs in the form of phosphates: connections between phosphorus and oxygen.

Especially for young plants, the presence of phosphate is necessary for the development of the plant. The largest concentrations of phosphorus are found in the plant parts that develop most strongly, such as the roots and shoots of the plant.

Phosphorus as fertilizer
In the past, ground bones were used as a fertilizer, but since these phosphates were not readily absorbed, they were treated with sulfuric acid, so that the phosphates became more readily available to plants. Nowadays phosphates for fertilizers are mainly extracted from phosphate-rich ores in North Africa and America.

There are different ways to make these phosphates suitable as a fertilizer. Since these natural phosphates often contain fluorine and cadmium in addition to phosphorus, which are harmful to many crops, it is important that they are purified.

Functions of phosphorus
Phosphorus is a chemical element that is also a macronutrient. This means the plant needs it in large quantities. You can imagine that a shortage of phosphorus directly results in a reduced growth of the plant. Not every crop has the same need for phosphorus. The most phosphate-needy crops are lettuce, spinach, onions and corn.

Especially at a young age, plants absorb a lot of phosphate for the initial growth. These phosphates are used for tuber formation, new root growth and the start of new shoots.

Phosphorus, or rather the phosphates, play an important role in the energy supply within the plant. They are the carriers of the energy released during photosynthesis.

How do you recognize a sulfur deficiency in plants?
A sulfur deficiency can be recognized by a light green discoloration of the leaves. At first the youngest leaves turn lighter in colour, then the oldest leaves. The symptoms of a sulfur deficiency initially look like the symptoms of a nitrogen deficiency, with the oldest leaves becoming lighter green. In the case of a sulfur deficiency, the youngest leaves turn lighter, after which the older leaves become lighter green.

At a later stage, the veins of the leaves and the leaf stalks become purple through the formation of the pigment anthocyanin. The light green colour of the leaves becomes deep yellow. With an extreme and prolonged deficiency, the growth and flowering of the plant also inhibits.

How do you recognize a phosphorus deficiency?
A phosphorus deficiency is not always easily to identify and is often confused with a nitrogen deficiency or a potassium shortage, in which the leaf edges also discolour first. In the case of a phosphorus shortage in plants, however, the stems and leaf stems show a purple color. The purple-black necrotic leaves divide the leaves and curl the leaves later. The oldest and somewhat less old leaves are first affected by a phosphorus deficiency.

At first the leaves turn dark green, after which a bluish haze comes over them. From the second to the third week, the purple-black necrotic spots develop further. In the period thereafter, the spots spread to the core of the leaf, curl up and died off.

Since the youngest shoots always get 'priority' due to a lack of phosphorus, the plant usually flowers completely, but the harvest remains poor and small.

Causes of a phosphorus deficiency
Phosphate is always present in the soil only to a limited extent and often in a limited absorbable form. This gives the roots a tendency to "get what they can get". When you grow on a hydro substrate, as a grower you can always give the optimal dose of phosphate, while growing on soil is more difficult. Shortages, however, hardly ever occur when using high-quality plant nutrients. Causes of a shortage can be:

Too high pH in the growth medium (> pH7) causes the plant to be able to absorb phosphorus, resulting in insoluble phosphorus compounds in the substrate.
A phosphorus deficiency often occurs in combination with a zinc deficiency, copper deficiency and / or a magnesium deficiency, because this will hamper the absorption of these elements.

What can you do about a phosphorus deficiency?
Inorganic phosphates, in contrast to organic phosphates, are very easily absorbed by the plant. For this reason it is advisable to use a qualitative fertilizer and mix it well through the soil.

If you have an alkaline substrate, then the soil can be slightly acidified by using a dilute solution of phosphoric acid.