NPK Soil Nutrient Balance: What Is It?

Striking the right NPK soil nutrient balance is crucial for healthy plant growth. In this article, we’ll consider:

  • Why is the NPK soil ratio important?
  • What is the optimal NPK soil nutrient balance?
  • How to find out NPK soil concentrations.

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NPK Soil Nutrient Balance: What Is It?

Healthy plants start with healthy soils, and to achieve this you need to find the optimal NPK soil nutrient balance.

NPK refers to the three major nutrients plants depend on to survive and thrive – nitrogen, phosphorus, and potassium. Plants need other nutrients as well, such as iron and calcium, but these three are required in the largest quantities.

The soil of lush gardens can therefore quickly become depleted, so it is necessary to replenish the soil with these essential nutrients regularly using a fertiliser.

What’s more, each plant’s nutritional needs are different, as is their growing environment, and these needs change as well throughout the growth cycle.

That’s why packages of organic fertiliser display an NPK ratio detailing the relative proportions of nitrogen, phosphorus, and potassium by weight. For instance, a 10 kg bag of organic fertiliser with an NPK ratio of 20:20:20 will contain 2kg of each nutrient.

NPK Soil Nutrient Balance: What Is Optimal?

As briefly mentioned, each plant requires different quantities of essential nutrients for optimal growth.

That’s because nitrogen, phosphorus, and potassium play different but complementary roles to support healthy plant growth.

Nitrogen helps plants make the proteins necessary to grow new tissues, in particular leafy tissues. Signs of nitrogen deficiency are therefore pale or yellowing leaves. So, if you are growing leafy vegetables or lawn grasses you should look for an NPK soil balance weighted towards high nitrogen content.

Phosphorus stimulates root formation, but it also helps plants produce flowers, fruits, and seeds, so larger quantities of it are required if you are growing, for example, tomatoes.

Potassium, meanwhile, boosts overall plant growth and promotes resistance to diseases and pests, so if your plants appear stunted or show signs of ill-health it could be down to a lack of potassium.

There are three main categories of NPK soil fertiliser ratios that you can apply to your soil.

A ‘complete fertiliser’ contains all three essential nutrients, but in different quantities to one another. A ‘balanced fertiliser’ has nitrogen, phosphorus, and potassium present in equal quantities, while an ‘incomplete fertiliser’ has one or two of these nutrients missing.

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NPK Soil Testing

Understanding the NPK soil needs of your plants is one thing, but it is also important to know how much of each nutrient is already present in your soil.

An NPK soil test kit can tell you the concentrations of nitrogen, phosphorus, and potassium in your soil so that you can more accurately determine how much of each you should add to boost your chances of a healthy, abundant yield. Then you can better choose which organic fertiliser or other organic nutrient product is right for you.

NPK Soil: Key Takeaways

  • Plants need nitrogen, phosphorus, and potassium in larger quantities than other essential nutrients.
  • Therefore, the soil gets quickly depleted of these three nutrients and needs to be replenished.
  • Different plants also require different quantities of nitrogen, phosphorus, and potassium, so fertiliser is typically sold displaying the relative proportions of each as an NPK ratio.
  • To help determine the right nutrient balance for your plants, you can use an NPK soil test kit.


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Spectrumlaan 39
2665 NM Bleiswijk
The Netherlands

T +31 (0)182 - 687 530
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