The (great) importance of nitrogen in plants

Surely everyone is familiar with the NPK complex, where the 3 most important minerals in plant nutrition are found. Nitrogen, phosphorus and potassium. Well today, as it was not going to be less, we are talking about one of the most important elements for the development of a crop, nitrogen . In nature we are presented with several types, so the time has come to unravel everything that can be told about this indispensable element.

eye! It is not mucus of turkey. We are talking about nitrogen occupying 78% of the content of the atmosphere and 3% of the human body. Unfortunately, not everything in the air passes to the ground, so we have to unwrap the cobwebs in our pockets to pay for nitrogen that can be assimilated by crops. Well … pay or create it .

The NPK complex that we have talked about so much in Gardenprue constitutes the primary subscriber of any plant. It is part of proteins, chlorophyll, hormones (such as vitamins), etc.

In short, an indispensable component.


The rocks that make up the Earth have very little nitrogen content. Something, in minimal amounts if we compare them with other types of nitrogen release, is released to the soil when the weathering of these rocks occurs.

However, what is really interesting is the fixation of atmospheric nitrogen (that 78% of which we have spoken). When we talk about fixation, what we mean is having assimilable nitrogen for crops.

This passage from atmospheric nitrogen to the soil can be done in two ways . On the one hand, there would be the biotic “path” , the one where the activity of microorganisms (both animals and plants) is vital to have this assimilable element.

There is also another way, the abiotic , where through rain, snow, etc., in general, atmospheric phenomena, such fixation occurs.

If you had to choose a fixation route, which one would you choose Undoubtedly with the great work carried out by microorganisms, the biotic pathway .

Of course, in our land there are not optimal conditions for the development of microorganisms.

Well, at least not so that these “bugs” are capable of creating nitrogen in sufficient quantities for the normal development of crops.


From the “common” point of view we could say that the meaning of nitrogen in plants is to create plant mass .

However, saying this is not technical at all, so let’s add a few more things. Thus we will see the true importance of this element in plants.

The most important role of nitrogen in crops is to be part of plant proteins (what we have discussed about creating mass …).

However, we cannot forget its role as a reserve , either in the seeds (its ability to endure “alive” without being planted or the energy it needs to transform itself into a plant once it is sown) or other reproductive organs.


It is involved in all these enzymatic processes:

  • Oxidases, catalases and peroxidases.
  • Dehydrogenases
  • Hydrolases
  • Nucleoproteins
  • Transphorylases and transaminases
  • Carboxylases

It stimulates the production of auxins, forms lignin, intervenes in the production of chlorophyll, etc.


Nitrogen fixation leaves an organic form in the soil that cannot be assimilated by any plant. Before that, it has to go through another “degradation process” where it goes from organic to mineral. 

When you hear the word “mineralization” in the future, you will know what it means.

With regard to these mineral forms, we are presented with two, which you will surely know:

  • Ammonia form (NH4 +)
  • Nitric form (No3-)

What we have in the ammonia form, over time, the action of the climate and microorganisms passes into a nitric form, easily absorbed by plants. However, this is all somewhat more complex:

The mineralization of organic nitrogen goes through several stages (aminization, ammonization, nitrosation and nitration), and we could summarize it with the fact that ammoniacal N passes to nitrous N and from there to nitric N.

Here microorganisms and soil quality intervene in an indispensable way, since without them it would be unfeasible to go from NH4 + to NO3-. There is nothing else left, take care of your soil microorganisms.


As noted above, plants absorb nitric nitrogen . Hence, many farmers use ammoniacal or urea type nitrogens as background fertilizer, since they are expected to remain in the soil as long as possible.

Another thing that we have not said so far is that this compound can be absorbed by the plant both at the root level (by the roots, the most common) and at the foliar level (in direct application).

However, the normal thing is that the application of nitrogen is done through the soil, both in ammonia (NH4 +) and nitric (NO3-) application.


Although it is not normal, there are plants that are capable of capturing nitrogen from the atmosphere, reducing it and transforming it into amino acids and proteins that will serve as food.

Rhizobium nodules on Vigna unguiculata . Photography: Stdout

According to Bermúdez de Castro , he established the following crops as fixers:

  •  Legumes (with Rhizobium ) as in the cultivation of broad beans .
  • Lichens (Peltigera, Lichina, Collena).
  • Azolla-Anabaena
  • Gunnera-Nostoc.
  • Grasses with azotobacter bacteria .
  • Gymnosperms with cyanophyceae .
  • Symbiosis between Phsychotria and bacteria.


Nitrogen deficiency is fortunately quite easy to detect. As this element has an action on chlorophyll, its deficiency causes the inhibition of green pigment production.

Consequently, we have leaves with complete chlorosis (remember the iron chlorosis , typical in many crops).

As nitrogen is closely linked to growth, if a plant lacks this element, we will find stunted plants that soon end up lignifying.

In general, to improve our diagnosis, the traveling leaves are the ones that show the first symptoms (chlorosis and lack of growth).

This is due to the fact that nitrogen is a very mobile element in the plant, so it easily moves to the points of greatest activity, from a functional point of view.


If we have been very brave applying this compound in our plants, they will present an exaggerated growth, greater development of shoots and branches (greater cell multiplication), more tender plants (less lignified), delay in the appearance of woody parts, delay in maturity, etc.

Therefore, if there are “softer” parts in the plant, it will be more susceptible to pests and diseases , it  will reduce the yield of the crop, it will produce lodging (cereals) or spiky (vegetables), it will be more sensitive to lack of humidity, etc. .


Special attention must be paid to the application of this very important element for crops. If we add a nitric form directly to the soil, as it is so mobile, it can easily leach, get lost due to the movements of water in the soil and, ultimately, not be fixed and not be used as it should.


When we need a quick response from the crop. The nitric form is absorbed very quickly and produces a rapid stimulus on the plant.

Poster that is still preserved in Andújar, Spain. PHOTO .

Ammoniacal forms are retained by the adsorbent complex and, therefore, the risk of losses is lower.

Of course, it has to go into nitric form so that it can be assimilated by crops. Well, it is not entirely correct, not always, since some ammoniacal forms are absorbed directly by the plant. However, in very small quantities.

Therefore, we are left with that the ammoniacal N has to pass to nitric N.


With this type of fertilizer we can apply nitrogen in ammonia form to the soil. The good thing it can have is that it contributes sulfur to the soil and is good for soils of a basic nature.

Those that already have an acidic pH abstain.


Ammonium nitrate was of interest when trying to vent all the explosives of World War II. It has a richness of between 33.5 and 34.5%, which is why it contributes a good amount of fertilizer units to the crop.

It is a widely used fertilizer since that 33.5% is distributed in 50% as ammoniacal N and the other 50% as nitric N

Are there only these fertilizers with nitrogen content? Strongly disagree. We currently have a lot of nitrogen-containing products on the market. The potassium nitrate , magnesium nitrate, monoammonium phosphate, the nitrogen solutions, calcium nitrate, etc.


Urea is a chemical form of carbonic acid diamide. Let’s say that it would be, within the nitrification process, at the top. Urea breaks down into ammonia and this, in turn, into nitric.

It has a minimum richness of 46%, so when it is applied to the crop, a significant amount of fertilizer units is added to the soil.

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