Compound or complex fertilizers


Today, in Gardenprue, we bring you some information related to compound fertilizers. Yes, the typical bag that we buy where there are some values ​​that we do not know how to interpret such as 12-12-12 or 20-10-5. Those values ​​are not randomly arranged and have a reason for being. We tell you how they are usually used and in what cases, as well as all the products that exist on the market.

We start by defining what compound fertilizers are and how they differ, for example, from the well-known compost  or manure of animal origin.

A complex fertilizer is a fertilizer that has more than one of the 3 main elements in agriculture and that we have already mentioned from time to time: nitrogen, phosphorus and potassium. The well-known NPK.

Therefore, it can have either 2 or 3. It is something different from binary fertilizers, those in which two simple fertilizers are mixed to contribute to the soil, with the consequent reduction of effort in its application. For example, in this case we could have ammonium sulfate, superphosphates, ammonium nitrate, potash sulfate, etc.

However, before its application we have to know the following:


The regulations governing the entire set of organic farming says it very clearly. Only those fertilizers that have natural origins will be part of this form of agriculture. If any of the compound fertilizers have a synthetic or chemical origin, they cannot be applied to organic farming. When in doubt, we can always consult the product labeling and what the European regulations say (if we are in Europe, of course) drawn up in  Regulation (CE) 834/2007.


Perhaps many farmers are led by the expert hands (or not) of the fertilizer product seller. Sometimes we just ask for a fertilizer for our crops and they give us a sack of something that we know is NPK but we don’t ask for it anymore. We see a series of values ​​that we do not know how to interpret and, to a certain extent, we do not care, as long as they work. What do these numbers mean?

It is very simple. These data inform us about the amount of each component. For example, a compound NPK 15-15-15 fertilizer is telling us that if we bought 100 kg of said product there would be 15 kg of nitrogen, 15 kg of phosphorus and 15 kg of potassium. That makes us think that we are adding the same amount of these components.

You should know that when we talk about nitrogen it is N, when we talk about phosphorus it is P2O5 and when we talk about potassium it is K2O. Also, if we see a value, for example, of 15-0-15, that zero informs us that it is a binary fertilizer that does not have phosphorus. Simple as that!


The application of these compounds is used by many farmers because they see some advantages that other elements cannot give them. For example:

  • Imagine that you have a very large plot and you have to make a bottom fertilizer. It would be too expensive to make 3 raisins applying each of the elements. In this way, applying an NPK it is possible to apply all the necessary fertilizer by the plants with a single pass.
  • When we apply these 3 elements at the same time, there is a positive association between them. As we saw in the article on plant deficiencies ,  there are antagonist and synergistic elements that modify mobility and its absorption by crops. Nitrogen, phosphorus and potassium are synergists between them.
  • They are prepared to have great mobility and be easily absorbed by the flat, so they correct deficiencies in a short period of time.


An important point is knowing when and which of all the different types of these fertilizers to apply. For example, if we do not want to have excessive nitrogen in the soil, we can apply fertilizers that have the first value of the 3 figures mentioned above much lower than the rest of the values. For example, we could apply an NPK of 4-12-8, 8-36-16, 8-15-15, 7-12-7, etc. There are many combinations.

If we want to incorporate a fast and effective fertilizer before sowing , we can have compound fertilizers with medium nitrogen content. They allow rapid germination and vigorous plant development. Different types of these compounds can be NPK 12-24-8, 12-12-24, 9-18-27, etc.

And finally, if we need to have nitrogen easily absorbed by plants in poor soil, or we need extra growth of plants that come out of winter rest, we can apply fertilizers with a good nitrogen content. Among these NPK fertilizers would be, for example, 15-15-15 (balanced content), 20-10-5 or 18-18-18 (also balanced content).

Hopefully it has been useful for those who had doubts or did not know how to apply these compound fertilizers. Do not hesitate to share it if you liked it! 🙂

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