Macronutrient phosphorus. Functions. Signs of Deficiency and Excess – Hydroponics

Phosphorus (symbol P) is one of the most important macronutrients necessary for the full development of a plant, second only to nitrogen. Phosphorus is a movable element, which means that it is able to move within a plant. When a plant is deficient in this element, the nutrient that is already inside the plant will be transported to where it is most needed – to the young tissues. Phosphorus is an integral part of plant cells and is required for cell division and the development of the growing top of the plant. It is vital for seedlings and young plants.

Phosphorus is an important constituent of proteins and influences the synthesis of starch. It is for this reason that plants in the flowering and fruiting stages require significantly more phosphorus. Phosphorus is most readily available to plants in an environment with pH values ​​from 5,5 to 6,5. Phosphorus becomes unavailable in highly acidic or alkaline solutions.

 

Phosphorus functions

Phosphorus promotes root formation and growth, affects the quality of seeds, fruits and flowers, and increases disease resistance. It is involved in several different plant processes, including genetic transfer, transport of nutrients. Phosphorus deficiency can create an imbalance in the storage of carbohydrates (sugar, starch, and cellulose). Photosynthesis usually remains normal under conditions of phosphorus deficiency, but functions within the cell usually slow down. An imbalance in phosphorus-deficient plants leads to the accumulation of excess carbohydrates within the plant, which is often observed when the leaves turn dark. In some plants, the leaf pigment can turn the leaves into a dark purple color.

 

Deficiency of phosphorus

Macronutrient phosphorus. Functions. Signs of Deficiency and Excess - HydroponicsInsufficient phosphorus levels disrupt genetic processes such as cell division and plant growth. Plants ripen more slowly than plants with sufficient phosphorus. Phosphorus deficiency will cause stunted and spindle-shaped growth, resulting in decreased leaf size and reduced leaf number. Deficiency symptoms include dull grayish green leaves and red pigment in the leaves. This coloration is caused by the accumulation of sugars that trigger the production of anthocyanins.

Phosphorus and nitrogen form important interactions. Low values ​​of phosphorus in solution lead to the accumulation of nitrogen in the plant, and vice versa. It is also true to say that excess nitrogen in solution will reduce phosphorus uptake.

Phosphorus deficiency symptoms can occur if the levels of zinc, calcium, and / or pH values ​​are very high. However, adding more phosphorus will not solve the problem. It is best to dilute the solution by adding additional water to the reservoir and adjust the concentration of other nutrients accordingly.

Phosphorus deficiency is difficult to diagnose, and by the time the signs are evident, it may be too late to do anything. If plants are depleted from the lack of phosphorus in the seedling stage, they may not recover later, even with a normal phosphorus diet.

 

Diagnosis of phosphorus deficiency

There are two main methods for diagnosing phosphorus deficiency – visual identification and analysis of the culture medium. While darker green leaves and purple or red pigment may visually indicate phosphorus deficiency, other environmental factors can cause similar discoloration symptoms. During cold periods, sugar buildup may begin in the leaves, indicating the same symptoms as phosphorus deficiency. In commercial growing conditions, phosphorus deficiency is usually diagnosed based on analysis of the solution – by removing a sample from the root zone. The extract is analyzed using colorimetry to determine the concentration of phosphorus. If the phosphorus concentration, as measured by the colorimetric test, is significantly below the optimum levels of the plant, then the plant is likely to be deficient in phosphorus.

 

Examples of symptoms of phosphorus deficiency

From left to right: phosphorus deficiency in corn, sweet potatoes, cotton, grapes, rice, strawberries, hemp.

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Macronutrient phosphorus. Functions. Signs of Deficiency and Excess - HydroponicsElimination of phosphorus deficiency

Correcting and preventing phosphorus deficiency usually involves increasing the levels of available phosphorus in the nutrient solution. Phosphorus levels are sometimes adjusted using phosphoric acid or a buffer solution used to control the pH of the solution. This solution is the pH minus Bloom additive.

 

 

Excess phosphorus

Phosphorus toxicity is rare in uncontaminated systems. An excess of phosphorus can manifest itself as a lack of trace elements (Zn, Fe or Co). High levels of phosphorus also inhibit nitrogen absorption.

 

Sources of

  1. Practical Hydroponics & Greenhouses . January . 2017.
  2. IPNI Crop Nutrient Deficiency Image Collection.
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Anna Evans

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