Fertilizers in agriculture. User guide and “recipes”

Today in Gardenprue, Eduardo, our collaborator, delights us with a very complete and accurate article on fertilizers in agriculture. We immerse ourselves in the world of plant nutrition, of the elements and macronutrients that every plant needs. Nitrogen (N), Phosphorus (P) and Potassium (K) and most importantly, their rational use, avoiding unnecessary poisoning and contamination. An article of those to sit down and end the day reading. 

Here, as at half past seven, I will not go over there.

Don Mendo: And a vile game

that you don’t have to play it blind,

Well, you play a hundred times, a thousand,

and of the thousand, you see feverish

that either you pass or you do not arrive.

And not arriving gives pain,

it indicates that bad rates

and you are from the other debtor.

But woe to you if you go over there!

If you go, it’s worse! “

Well, in our case it is the same. Going over is equal to contamination, waste, poisoning of plants, soil and even groundwater. There are about 17, or no, 17 to dry essential elements for plants, the three most important are the NPK complex.


N = nitrogen, from the Latin ” nitrum” , but the gas was not known, but it was applied to its salts, it is possible that it was applied to the excrement, especially of birds, because there is already reference in Greece and later in Rome of them . The most important and well-known accumulation of bird feces is Nitrate from Chile,  also known as guano or white gold, although the first site to be exploited was in some Peruvian islands, exploited even today in a rational way. It even caused a war between Chile, Peru and Bolivia, the Pacific or Nitrate War, in which Chile removed the Atacama Desert from Bolivia and its exit to the sea. Later, during the great war, the Germans paid privateers to sink ships with nitrates, with which explosives are made.

Typical Chilean Nitrate ad

In 1918 the chemist Haber received the Nobel Prize in Chemistry for the synthesis of ammonia . Curiously, he was the developer of gases during the 1st world war, as a result of this his wife and son committed suicide. If someone is curious they can search for “iperita” or “mustard gas” or “dichloro gas.

Nitrogen is used by the plant to form organic compounds, essential amino acids when it comes to forming proteins. Nitrogen is highly polluting, it is degraded and leached to deep layers, penetrating the aquifers, forming nitrates, carcinogens for the little ones, and nitrites that usually reveal the presence of fecal bacteria.


P = phosphorus, from the Greek Phosphorus, which carries light, remember that it is “phosphorescent” and is in the bones. But not only they, it is also part of AMP, ABP ATP, adenosine mono, bi and triphosphate that are the molecules that carry out energy exchange, in animals and plants , through smaller jumps so that we make better use of the energy stored in the molecule. If you want more information look for “phosphorylation”. P is part of chromosomes , DNA, and other equally essential molecules.

If we count that the US consumes 70% of phosphates in fertilizer and we add soaps and other products, we are facing a consumption of 75 to 80% of phosphates only in the US, without comment.

Phosphorus is essential for plant growth, although they only form between 0.1 to 0.5% of the total, however it is present in all corners of the plant, whether stored or present in all phosphorylation processes. A molecule of ADP captures energy from the sun, in the leaf, photosynthesis, and produces another one of ATP that is richer in energy and useful for other processes, remembering the absorption of water by the roots, always in the presence of oxygen.

Subscribing with P guarantees us new cells and something important: the development of seeds and fruits , since phosphorus is stored in them in the form of phytin, which is why its deficit usually causes smaller fruits and seeds.


K = potassium, (from the Latin Kalium  and the Arabic al-qalya). If we pronounce the word quickly and repeatedly we arrive at “alkali” which identifies “base” in chemistry. It has also been translated as “plant ash”, but I think it would have more to do with the artisan making of soap made with “plant ashes”. Soap, after all, is made with an alkali that is obtained by burning plants. Once explained everything seems much simpler, right?

Potassium is important for various processes, it is responsible for regulating evaporation, opening and closing of stomata, in starch and forming the “sodium-potassium pump” in which, through ADP, ATP and a Inorganic phosphorus is responsible for the intracellular transport of inorganic ions. It is an essential part of a cellular protein that is in all living beings.

Notice that all these previous things that seem disconnected and uninteresting translate into the fact that, thanks to the Na-K pump, we have evolved animals and we are what we are, since they allow a transmission of electrical signals between cells, synapses between neurons. .


When I wrote No PeKar I made a play on words to indicate that it is better not to arrive than to go overboard. If we spend too much, we lose what is dissolved in the irrigation water, which always some fraction dissolves and goes away, therefore when we pay in a lower dose we will lose less fertilizer. Here we are not talking about a large plantation in which it pays to carry out a chemical analysis.

I normally use half the dose that is advised on the package and, at most, half the amount stipulated , so I pay a quarter of what they tell me, and things are not bad for me. I am even three to four months without paying and I do not notice differences. Let us remember that both the earth and the plant are a storehouse of mineral elements.

Another different thing is the imbalance, that yes that is painful for the plant. Let’s think that the plant takes the minerals in the proportion in which it needs them, one part stores it, another remains in the ground. What happens if a synergistic mineral is missing with another?

RAE (dictionary): synergy: 2.  f. Biol.  Active and concerted competition of various organs to perform a function. 

Let us replace organs with essential elements and we see that if we lack one, the function is not carried out even if the others are present. To make matters worse, it turns out that the excess of some of them can become toxic due to being in excess and not being able to be absorbed by the root. Caution, then, when we buy a fertilizer for flowering richer in phosphorus, remember the phytin, different for green (green = growth) very rich in nitrogen, or for autumn poorer in nitrogen so that the plant becomes harder and better withstands cold.

With all the above it is not easy to say, now pay with this, now with the other, remove N and put K, no, this works with common sense. Fertilize just and balanced and, if you want a spectacular flowering, of HEALTHY PLANTS, use a fertilizer indicated for flowering.

If we do not want the seeds, as in the case of roses, we cut the flower dry to avoid greater consumption and loss of energy from the plant that best uses it in its growth.

Be very careful with the ashes, if you want to add them to a compost it seems good to me, directly on the ground next to the plants is not advisable, too many elements too fast, it causes toxicity and we do not know the composition of the ashes. The pH also rises, which is not advisable in our latitudes, which is already quite high.


Now in March I am going to prepare a complex: dissolved iron, foliar fertilizer and if I notice any deficiency I will incorporate it. With 100 liters of compost wetting all the foliage and watering the land, just over 100 m².

I keep a part for all the potted plants, well outside, well inside, I do not distinguish.

In June if the weather is very warm, I add another fertilizer, usually slow release, between half to a kilogram for the garden. Indoor plants continue with foliar fertilizer, yes, the best since, due to its value, it will last 2 to 3 years and each fertilizer is quite cheap.

I have no frosts, some cold that is around 0º 0 -2º C for a short time, with some extemporaneous and short snowfall, so I don’t need a strong potassium fertilizer in autumn. I go back to playing with balanced fertilizers and foliar fertilizer, especially in those plants in flower or that are going to have it.

But, if in your case you have frosts, a poor fertilizer or nitrogen-free and rich in potassium should be used.

The rest of the elements can be added with the foliar fertilizer and, with exceptions, you will have the deficiencies covered. But I will tell you that each microelement leaves a characteristic mark on plants, just as the yellowing of the leaf is a lack of iron (Fe), (SOLE, it is not always true), boron (B) also causes yellowing but in another way or magnesium (Mg), the deficiency is first noticed in the old leaves and then it is transferred to the rest, towards the ends of the branches.

There are deficiencies due to the absence of another element, I already said it, or because it is blocked on the ground. As all this is very interesting, I will try to study it, look for photos, which is not easy, and tell you how the rest of the chemical elements work.


What is the difference between one N from an inorganic compost and another from a biological compost? Or in general, what is the difference between fertilizing chemically or organically? In principle, the plant does not distinguish one from the other, but not even the best chemical or clinical laboratory in the world with the best analysts would find the difference.

Let us start from the essential premise that the periodic table of the elements, Mendeleyev , is invariable, it does not distinguish atoms from one place or another, the plant will not therefore take from here or there. Where, then, is the difference? Everyone who has an opinion and stay tuned because we will give the answer in a few days.

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