Fertilizers Talk

What are NPK Fertilizers?

what are npk fertilizers

There are fertilizers that are natural, like manure, and fertilizers that are man-made. NPK fertilizers are fertilizers that contain the elements nitrogen (N), phosphorus (P), and potassium (K).

Why these elements? Well, each element has been found to improve the health and appearance of plants. For example,

  • Nitrogen is good at making the leaves grow.
  • Phosphorus improves fruit and/or flower production as well as root growth.
  • Potassium is great for overall plant health.

 It’s also about making a decision about the right formula with the right ratios of nitrogen (N), phosphorus (P) and potassium (K). Although compost, mulches, manure and other organic matter contain many of these nutrients, there still may be deficiencies. The amount of supplemental feeding necessary depends on the condition of the soil and plant needs. Fertilizers are supplements to healthy, living soil, not a solution to plant nutrition. Now let’s talk about N,P and K individually-


Nitrogen is considered to be the most important nutrient, and plants absorb more nitrogen than any other element. Nitrogen is essential to in making sure plants are healthy as they develop and nutritious to eat after they’re harvested. That’s because nitrogen is essential in the formation of protein, and protein makes up much of the tissues of most living things. Below is a picture of corn that is nitrogen deficient. 


A stimulant for root growth, seed and flower formation, phosphorus is most available to plants when the soil pH is between 5.5 and 7. The pH refers to the acid or alkaline level of the soil, and can range from 0 to 15 with 7 regarded as neutral. Different from nitrogen, phosphorus tends to remain in the soil; add it only for new growth. Root vegetables, such as carrots, use large amounts of phosphorus, particularly during early growth.


Potassium promotes root and bud growth and ripening of fruit. It enhances disease resistance as well as tolerance to drought, heat and freezing. This element is essential for all plants to thrive, particularly in changing weather conditions. Potassium also has a tendency to remain in the soil, but is heavily used by growing vegetables, so should be supplemented as needed, based on a soil test.

There are two types of NPK Fertilizers:

Solid NPK fertilizer delivers its nutrients slowly. Thus, it has a long-term effect, which many horticulturalists appreciate. Rain does not wash it out of the ground as fast. Thus, it is ideal for outdoors. This kind of fertilizer is usually administered to the plants through the so-called process of top-dressing, which means that the product is sprinkled evenly over the entire surface of the soil and not worked into it. Deep fertilization is only preferable for deep-rooted plants (such as fruit bearing plants and trees) in order to supply the roots with more speed and effectiveness. Using solid fertilizer also raises the question of point fertilization.

Liquid NPK fertilizer is mostly used with potted plants and rarely with outdoor cultures. Then, both the watering method (liquid fertilizer is added to the water) and point fertilization, which supplies selected individual plants, come into question. Another method is the so-called foliar fertilization method (onto the underside of plant leaves), which is only recommended for a few plants.

Why is it important for farmers to know the NPK content in their soil?
For the optimal growth of crops, sufficient amounts of nutrients should be available in the root zone of the crops. Those nutrients can be partly supplied by the soil and should be partly added with organic manures and fertilizers. Soils will contain different amounts of available nutrients, depending of the parent material (e.g. sand, clay, peat), and differences in the management history such as preceding crops, management of crop residues and use of manure and fertilizers in the past. Also differences in climatic conditions may alter the available nutrients. For that reason, it is of importance for farmers to know the NPK content of their soil, so that they know how much N, P and/or K they should add with organic or mineral fertilizers, to optimize crop growth, production and yield.  

Conclusion: Compound fertilizers (NPK) have, apart from the slightly higher price, many advantages. They are easy to use and rich in nutrients; they should be used where there is a specific lack of all the main nutrients. If that is not the case, you can also use binary fertilizers or nitrate fertilizers. These have only two (e.g. potassium and magnesium) or even just one essential nutrient (e.g. nitrogen) and are therefore often not as expensive as NPK fertilizers.

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