What fertilizers are incompatible with each other? (compatibility table)


In the market we can find a large portfolio of fertilizers and fertilizers to apply by irrigation or foliar application. However, we must not forget that we are “playing” with chemicals and, therefore, there are certain incompatibilities.

We take a little nitric acid, we mix it with urea, some calcium that is good for plants and, of course, a little bit of phosphoric acid that will also be good for them. We mix it and we find a precipitation of the liquids that will take us centuries to remove. And, also, with an obstruction of our drippers that we will have to solve manually or with these methods .


Although it is already a trite subject in Gardenprue, it does not hurt to remember it again. In the sacks of fertilizers and fertilizers that we can buy in agricultural warehouses we can see numbers that not everyone knows how to interpret.

In addition, in the market we can find many ways to get to the same place, but by different ways.

Let’s say, for example, that we need to contribute 100 FU (fertilizer units) of nitrogen to a crop, with which, we can do it in several ways:

  • Ammonium nitrate
  • N-32
  • Ammonium sulfate
  • Nitric acid

All these forms, with their different composition, are ways of supplying nitrogen. And that we have given this specific example, because we could also have done it with phosphorus and potassium, as they are the main macronutrients.

Now, what differences can exist between one and the other?

With ammonium nitrate (33.5% – 34.5%), we provide a part as  ammonia nitrogen and another part as  nitric nitrogen . That is, nitric is the simplest and most assimilable form, and the one that will have the fastest effect on the crop. Ammonia needs to  nitrify , that is, oxidize ammonia to nitrite.

Don’t worry, we will not do that, but the temperature, the silent microorganisms, etc. 🙂

With ammonium sulfate we provide all the nitrogen content (21%) in ammonia form, so it will not act as quickly in the crop. In addition, we will contribute sulfur (60%) to the soil, interesting for alkaline soils (but not for acid soils!).

We have already been able to distinguish between two fertilizers that provide nitrogen to the soil. Now, to reach 100 UF of nitrogen, different kilos of these fertilizers will have to be added:

  • Ammonium nitrate (33.5%): 298 kg
  • Ammonium sulfate (21%): 476 kg

The less kilos are contributed, the cheaper?

It all depends on how the market is. If we do not care to use one or the other, it will depend on the prices of each subscription to decide. To continue with the previous example, if ammonium nitrate were at € 0.35 / kg, we would pay € 104.3 to complete those 100 UF. On the other hand, with ammonium sulfate (€ 0.22 / kg) we would pay € 104.72. Almost equal!


Now, the previous example of knowing how to distinguish and choose between different fertilizers that provide the same nutrient (nitrogen in this case) does not end here, because now we are going to what we wanted to talk about in the article: incompatibilities .

Let’s take the case that we want to add an NPK to our fertilizer in order to be able to provide the crop with the main nutrients it needs.

In this case, it would be necessary to study which fertilizers are compatible or not, so as not to have mixing problems.

Let’s see the following image.

First, clarify one thing:

I: incompatible.

X: limited compatibility. This means that they can be mixed at the time of fertilization, but not leave mixed for long.

C: compatible. Everything Ok! 🙂

If we want to fertilize with  ammonium sulfate because we want to decompose the organic matter that we have and, in addition, increase the pH of the soil to release certain microelements, we must bear in mind that we cannot mix it with  calcium nitrate (a very common fertilizer) or with  monoammonium phosphate . The latter, we could do with ammonium nitrate .

Calcium has always been very bloody . There are times that no matter how much we contribute Ca to the soil, we get problems and deficiencies in the crop because the plant is not able to mobilize it . Even in humans it is the same and it is difficult to fix it, so they often add vitamins to help in its assimilation. The same thing happens in agriculture, only they add chelating elements or cytokinins to facilitate root (or foliar) absorption.

With the rest of fertilizers it also gives problems. It’s very bloody. Often, it forces the farmer to have a second fertilizer spreader or to fertilize first with a mixture and then another alone for calcium.

As you can see in the table, it is incompatible with almost everything, except for nitric acid, potassium sulfate and urea, where the latter two must be done at the time of payment.

Imagine that we mix ammonium sulfate with calcium nitrate. What do we get in our vat? Cast!

And nothing more! We just wanted to offer this interesting table that should be printed on every sprinkler head and the farmer has to brood it.

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