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The Ultimate Guide to Phosphorus Fertilizer

Discover the essential role of phosphorus in plant growth, its benefits, application methods, and precautions in our comprehensive phosphorus fertilizer guide.

We have all heard about phosphorus fertilizers. But only a few know why it is added to the plant soil. Phosphorus is essential for the plant; it is one of the few nutrients without which a plant cannot function optimally. What are those functions, and how do they work? Is there a specific time or precaution one must take when adding phosphorus to the soil? 

To learn this and more, read this guide to the end. We have penned down the role of phosphorus in plant life, its benefits, etc. We have also covered what happens when a plant doesn’t get enough phosphorus. So, keep reading. 

What is phosphorus fertilizer?

Phosphorus, as we know, is a chemical element present in a fertilizer. It is one of the 17 essential ingredients required by a plant to grow and flourish. 

Its concentration in crops may range between 0.1 percent to 0.5 percent. 

Types of Phosphorus Fertilizers

Types of Phosphorus Fertilizers

Organic fertilizers

These are good resources for phosphorus, but they must be turned into simpler forms before the plant ingests them. For example, mycorrhizal fungi. They build colonies on the root cells and spread out in the form of filaments. The latter absorb phosphorus and move it into the root cells. The plant provides them with sugars produced via photosynthesis. 

Best sources: bone meal, colloidal rock phosphate (soft rock phosphate), high-phosphorus bat guano, and crab shell meal.

Inorganic fertilizers

Inorganic phosphorus fertilizer works completely differently. These are useful when the plant has excess water-soluble phosphorus present in the root area. In such cases, the plant releases enzymes to fend off mycorrhizal fungi and absorbs all the phosphorus it needs for its growth.

Best source: calcium phosphates in alkaline soils and aluminum, iron, and manganese phosphates in acidic soil. 

Fast release fertilizers

Water soluble is also known as ‘Fast Acting.’ It is the most easily available phosphorus form. 

Best sources: Horse or chicken manure, fish emulsion, bone meal, and rock phosphate

Slow-release fertilizers

These are also called superphosphate. The word slow depicts the slow action. To elaborate, the phosphorus in slow-release fertilizer needs to be dissolved using another method. These may include soil microorganisms. 

Best sources: urea formaldehyde, methylene urea, and nitroform.

NPK ratios and how they relate to phosphorus content

The NPK are the three main elements in fertilizer and stand for Nitrogen, Phosphorus, and Potassium. For example, an NPK fertilizer 15:15:15 depicts 15% nitrogen, 15% phosphorus, and 15% potassium. 

So, if you want to enhance your plant’s growth, buy an NPK fertilizer with higher phosphorus levels such as a ratio of 1:2:1. 

Why is phosphorus important for plant growth?

Why is phosphorus important for plant growth

Every plant cell contains phosphorus. It is needed to carry out several functions that affect a plant’s growth and proliferation. Some of these processes are vital to plant health, such as the movement of nutrients, photosynthesis, sugar formation, and, most importantly, the transfer of genetic information from one plant generation to the next. 

Energy transfer 

Any plant process that is directly or indirectly related to energy transfer requires phosphorus. It is an important element in the chemical composition of ADP (adenosine diphosphate) and ATP (adenosine triphosphate). As these two molecules move phosphate to other molecules, it paves the way for several chemical reactions to take place. 


Plants use sunlight to make their food. They use chlorophyll, a green ingredient, to combine water and carbon dioxide to capture light in ATP. This allows plants to develop new parts, such as roots and leaves. 

Transfer of plant genes

This vital element is also vehemently found in the chromosomes of a plant’s genetic material. It is a part of the genetic code that has all the hereditary data. However, a plant needs lots of phosphorus to develop new cells and pass on genetic information.

An example of this is the seeds and fruits. They contain huge amounts of phosphorus.

Nutrient transfer

We know that nutrients move from one part of the plant to another through cell membranes. However, these membranes require ATP and other phosphorus-containing ingredients to carry out the processes. Again, phosphorus is used.

Deficiency of Phosphorus

The three most significant deficiencies found in plants due to insufficiency of phosphorus (P) element are:

  • Stunted growth, characterized by smaller leaves with reduced surface area
  • Fewer leaves in total, and
  • Sorter shoots

This is how it happens.

If a plant does not get enough phosphorus, this can slow down how it uses carbohydrates. 

Carbohydrates are essential nutrients made by plants using the process of photosynthesis. But when phosphorus is lacking, these can build up. This makes the leaves develop a darker hue. In some plants, it might even turn purple, such as sometimes seen in corn or tomatoes. 

Also, in the absence of enough phosphorus, the plant transports it from older parts to the growing parts. This makes the older parts exhibit signs of deficiency. However, this is rare; you may not see it in the field crops. 

Benefits of using phosphorus fertilizer

Benefits of using phosphorus fertilizer

When you add phosphorus to your crops, it: 

  • Aids in optimum production of chlorophyll through photosynthesis
  • Builds the genetic material such as the nucleic acids, proteins, and enzymes
  • Helps in the development of roots
  • Increases the strength of stems and stalks
  • Enhances the formation of flowers and the production of seeds
  • Supports consistent growth in crops
  • Helps in the early maturation of plants
  • Makes the plant resistant to diseases
  • Boosts the overall quality of crops
  • Helps legumes absorb nitrogen

How to Apply Phosphorus Fertilizer

There are five phosphorus application methods to nourish your plants with phosphorus:

Banding method: This method is often used to fertilize plants in the spring or fall just before you sow seeds. You can use shovels or knives to cultivate the soil 8 to 10 mm deeper. When phosphorus is applied in bands, it is found to be less effective. Nevertheless, it is still better than sprinkling fertilizer all over the field manually. 

Side banding phosphorus: In this method, the phosphorus is placed just close to the seed row. The space is generally kept at 2.5 to 5 cm (1 – 2 inches) either to the side or just below the band. This method is considered ideal for growing sensitive plants such as potatoes, sugar beets, corn, sunflowers, and beans. 

Broadcast and incorporation: The method infamously uses the technique of fertilizing before seeding. The downside of using this method is that you are required to use two to four times more fertilizers than the above methods. However, it helps in improving fertility in eroded soils. The initial cost may be high, but it is worth it over some time.  

Top Dress: As the name suggests, this technique proceeds without incorporation. It works better for forage plants with well-established root and shoot systems. You can broadcast granular phosphate, whereas liquid phosphate can be dribbled. 

Side-placed phosphorus: With this, phosphorus can be placed optimally for oilseed and cereal crops. For oilseeds, the phosphorus rate should not cross 15kg/ha, and for cereal crops, it is 50 to 70 kg/ha. Also, peas should have 30-35 kg/ha. 

What is the Right Time to Apply Phosphorus Fertilizer?

The spring and fall are the best times to fertilize your plants. However, in the spring, the soil is wet. It may not be a good idea to dig the soil as it may lead to some issues. Therefore, consider fall. This is because the soil is drier for tilling.  

Even if you do not dig the soil, you can still add phosphorus fertilizer to the soil. This gives it ample time to go deeper into the soil and prepare the soil for spring plantation. Thus the plants receive phosphorus more effectively. 

Is there any other way to know that it’s time to add phosphorus? 

Yes, you can try soil testing. Here’s how you can do it. 

Apart from knowing the insufficiency, a soil test can help you learn about the nutrient concentrations, as they may vary. The three methods for testing soil include:

  • Bray P1 test
  • Mehlich 3
  • Olsen P 

Out of the three, the Bray P1 test is the most commonly applied soil testing method for knowing phosphorus presence.

Safety Precautions when Handling Fertilizer

  • Always wear glasses
  • Do not touch the fertilizers with bare hands. Wear impermeable gloves
  • If it comes in contact with the eyes, wash it immediately. If case burning persists, visit a doctor immediately.

What Happens When You Apply Phosphorus at the Wrong Time

What Happens When You Apply Phosphorus at the Wrong Time

Over-application or application at the wrong time can be disastrous. For instance, if you fertilize your lawn right before it rains, then a majority of it will end up in the water bodies. Experts call this nonpoint source pollution.

This kind of pollution reduces the amount of oxygen in the water, making it difficult for aquatic animals to breathe for a long and they die. Knowing that organic matter and minerals are bad for the environment, it has been banned in many places, especially for lawns.

Some Common Myths about Phosphorus Fertilizer

  • Adding phosphorus to soil helps in its growth only if the soil has insufficient amounts of phosphorus.
  • Phosphorus does not promote root development in plants. Their presence in starter fertilizers does not make them a go-to nutrient for roots.
  • Your garden soil has enough phosphorus in it. This means adding more is useless and harmful to the environment.  

Parting Thoughts

With that, we conclude our guide on phosphorus fertilizer. Remember, the soil does not have enough phosphorus. Therefore, it must be added if you are looking to boost your crop yield. However, there is a specific time and plan for application. Follow it and make sure you do not over-apply it. If you follow these points, there is no way you will face any issues. Apart from this, make sure you choose the right fertilizer manufacturer for your fertilization requirements. 

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