What Is The Role Of NPK In Plants

It’s no secret that gardeners all hope to achieve the highest yields. One of the surest methods to succeed is to start with soil perfectly suited to the needs of the plant about to grow in it. But how do we achieve this?

There are so many different types of soil additives – some that help to aerate the soil and regulate moisture levels, others that protect from infestations or disease, and finally, fertilizers to promote growth.

So, which is the best fertiliser for the plant we are about to grow? This depends entirely on the existing soil and the type of plants you want to grow.

Before choosing a fertilizer, experts recommend testing the soil. This will determine which nutrients are already present in the soil and which will need to be added.

This is where the fertilizer comes in – chemical and organic fertilizers add the macronutrients and micronutrients essential for healthy plant growth.

What are macro and micronutrients?

Contrary to what is often taught in science classes, plants require far more than just water, sunlight, and carbon dioxide to thrive. In fact, we know of more than a dozen nutrients that are essential for plants to flourish.

These are grouped by the amount required and taken up by the plant. Macronutrients are consumed in relatively large amounts of between 10 and 100 kilograms or more per hectare of soil; micronutrients are typically taken up in far smaller amounts – only several grams per hectare.

The known plant micronutrients are Manganese (Mn), Boron (B), Copper (Cu), Iron (Fe), Zinc (Zn), Nickel (Ni), Molybdenum (Mo) and Chlorine (Cl).

There are six macronutrients necessary for plants: Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), and Sulfur (S). The most important of these are the first three listed.

Why is N, P, and K so important for plants?

These nutrients are required by crops in the largest amounts. They support the most essential functions of the plant, protecting it, and promoting its growth. This is especially true if the plant requires a lot of nutrition to grow properly – for example, if growing potatoes.

In fact, these nutrients are so important to healthy plants that all commercially available fertilisers list the amounts of nitrogen, phosphorus, and potassium that they contain; for example 10-10-10, 20-0-10, or several other combinations of numbers. These represent the nutrient content.

The higher the number, the more concentrated the nutrient will be within the fertilizer. The fertilizer numbers can be used to calculate the amount of fertiliser needed to add 1 pound of the nutrient into the soil – simply divide 100 by the number listed to calculate how many pounds of fertilizer are needed to increase the nutrient level by 1 pound.


Nitrogen is paramount to plant health – it’s a core component of the plant structure and vital to metabolic processes, such as photosynthesis.  

It’s an essential element of all the amino acids in plant structures; these are the building blocks of plant proteins and are important to the development of plant tissues such as the cells, membranes, and chlorophyll.

This means that plants with sufficient levels of nitrogen experience higher rates of photosynthesis, and will typically grow and develop vigorously.

Nitrogen is also a factor in the development of DNA, which contains the genetic blueprint of the plant – it’s a component of nucleic acid.

Nitrogen Deficiency

Plants can neither use nor take nitrogen directly from the atmosphere – it must be absorbed from the soil through nitrogen forms that include ammonium and nitrate.

An insufficient supply of nitrogen can lead to several plant disorders. As nitrogen promotes the creation of chlorophyll, a lack of it will affect the plant’s ability to create sufficient starch and proteins.

This undermines the overall health of the plant and will also affect flowering and fruiting.


Like nitrogen, phosphorus is an essential nutrient to plant structure and a catalyst for numerous biochemical reactions – especially photosynthesis. It’s also a crucial element for both DNA and RNA, the compound that reads the genetic code.

Phosphorus is a central component of ATP, which forms during photosynthesis and provides energy to the plant from the very beginning of seedling growth through to maturity.

Phosphorus improves the overall crop quality and supports plants throughout their life cycle, stimulating root development, increasing the strength of stems and stalk, supporting flowering and the production of seeds as well as contributing to an earlier and more uniform crop maturity.

Phosphorus Deficiency

Other than stunted growth, plants display no obvious symptoms of phosphorus deficiency – it’s therefore difficult to diagnose visually until it is too late to correct in annual crops. The best way to detect a lack of phosphorus is through soil testing.

Some crops, such as corn, may be discoloured when they lack phosphorus – the plant will usually take on a dark bluish-green cast with purplish leaves. When phosphorus deficiencies occur late in the growing season, it can affect the pace of maturity as well as the formation of fruit and seeds.


This essential nutrient contributes to the proper growth and reproduction of plants by aiding in the activation of growth-related enzymes in plants – the level of potassium in the soil can affect the shape, size, colour, and even the taste of the produce.

It has several other roles. Potassium regulates the uptake of carbon dioxide during photosynthesis and triggers the enzymes involved in the production of ATP as well as the synthesis of proteins and starches.

Potassium also helps to regulate the level of water in the plant, affecting both the uptake of water by the roots and its loss through evaporation; it can therefore improve a plant’s tolerance to drought.

Potassium Deficiency

A lack of potassium will typically affect the growth of the plant but may cause other abnormalities. Potassium deficiencies can result in weak and unhealthy roots, which may slow or stunt the plant’s growth as well as leave it more vulnerable to pests, drought or temperature changes.

One of the first visible symptoms of potassium deficiency is chlorosis – scorching and yellowing margins on the middle and lower leaves. If untreated, the plant may lose its leaves sooner than normal, and fruit will ripen unevenly.

Choosing a fertiliser that provides these essential nutrients in the proper quantities is the best way to ensure that crops flourish and provide the highest possible yield.

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