One of the nutrients that we abuse the most and have the most visual effect on our plants is nitrogen. Hence, a nitrification inhibitor technology has been in development for a few years . 

It is for the latter that, unlike many others, it is used many times without measure and with some abuse. Hence, many plants have an exaggeratedly fast growth and with a lot of formation of leaves and stems but are unbalanced with respect to the rest of nutrients. 

In the nutritional balance of a plant lies the success, not always the ‘generous use “of a nutrient will make our crops are stronger or produce more.

+ The great importance of nitrogen in plants

THE DIFFERENT PHASES OF NITROGEN

When we apply organic matter to a soil (be it animal or vegetable), together with fertilizers that contain nitrogen, we are applying different phases of this element that have a totally different behavior in the soil.

That is why it is necessary to know how to manage what phase of nitrogen to apply according to the time in which we are.

One of the concepts that we traditionally have is that plants can only assimilate the nitrogen phase known as nitrate (NO3-), one of the easiest to absorb within the catalog of fertilizers that we apply exogenously.

However, many studies and research have long told us that the ammonia phase can also be absorbed by the plant . In fact, almost as easy (often by passive diffusion) as the nitric phase.

In fact, a good starter fertilizer , which favors a fast and adequate rooting , would include a mixture of equal parts of the nitric phase (NO3-) and ammonia (NH4 +).

The first, the nitrate form (NO3-) favors the elongation of the lateral roots, those that improve the assimilation of nutrients. On the other hand, the ammonia form (NH4 +), when absorbed, favors the formation of new roots.

The ammonia form is interesting because, when it is absorbed by the roots, it directly becomes part of the plant’s metabolism. On the contrary, nitrate (NO3-) must be transformed, in a contrary process, to ammonia form (NH4 +).

The problem comes when the ammonia form is volatilized in the form of ammonium (NH3 +) or is absorbed in large quantities, becoming toxic to plants when it exceeds an absorption threshold.

It is considered advisable in conventional agriculture (in soil) that the ammonia form does not exceed 20-30% of the total nitrogen supplied. However, it all depends on the soil conditions, organic matter content (presence of nitrifying bacteria, temperature, etc.).

In hydroponics , this amount is further reduced, and it is not advisable to work with more than 10% in the ammonia phase, since in inert soils (coconut fiber, perlite, vermiculite, etc.), nitrification is not considered important due to low presence. decomposing organisms.

More than explaining the different phases of nitrogen in the soil and their behavior, we put a picture.

Contrary to what is usually thought, the transformation of nitrogen into ammonia form (ammonium sulfate, for example) does not go directly to nitrate.

An earlier phase , known as the nitrite form (NO2-), is necessary before moving to nitrate. Many times we have not heard of this form of nitrogen and, in fact, it is not the most important.

This happens because the process of transformation of ammonia (NH4 +) to (NO2-) occurs at the same rate as from NO2- to NO3-. Therefore, it is constant on the ground.

What is understood by nitrification inhibitors is to modify the behavior of the bacteria that intervene in the degradation process of the different nitrogenous phases.

However, as you can see in the image, there are 2 different types of bacteria or genera of bacteria that modify nitrogen.

1ST STEP: FROM AMMONIUM (NH4 +) + NITRITE (NO2- )

This nitrogen oxidation process is promoted by bacteria of the nitrosomonas type . They are bacteria known as ammonia oxidants.

In this process, it is interesting to help control the release of this element with nitrification inhibitors.

2ND STEP: FROM NITRITE (NO2-) TO NITRATE (NO3-)

In this step the oxidation of nitrite to nitrate occurs, promoted by bacteria of the genus Nitrobacter.

Both types of bacteria, nitrobacter and nitrosomonas , are quite differentiated and nitrification inhibitors will act differently.

LOSSES IN THE DIFFERENT NITROGENOUS PHASES

The great demand for nitrification inhibitors is based on controlling the transition from the ammonia form to the definitive nitric form (in several steps, as we have seen), so that it does not occur uncontrollably and in a matter of days or weeks , as happens in many of the soils that we have in Spain.

At first, we might think that what we are interested in is having all the nitrogen we can in nitric form, since it is the form that is most absorbed by plants. However, from a chemical point of view we have a problem. 

As you know, the  clay-humic complex has a negative electron charge or affinity. That is, all the nutrients that are cations will be trapped in said complex and will offer resistance to washing or leaching.

We can see it in the following image:

They are calcium, magnesium, potassium, iron, zinc, ammonia nitrogen (NH4 +), etc.

However, the nitric form (NO3-) has a negative charge , so it would not be fixed in the clay-humic complex, ready for a future exchange with the roots, when they give up hydrogens (H +) to compensate the electric charges.

When applied in fertigation, or when the ammonia form (NH4 +) of nitrogen is transformed into nitric form (NO3-) after passing through the form of nitrite (NO2-), it would be irretrievably at the mercy of the irrigation water. 

Hence it is said that in the management of nitrogen (nitric), it is essential to control irrigation to the maximum. 

Therefore, in extensive crops, irrigation to blankets or areas where there is a lot of rainfall, the application of ammoniacal nitrogen to the soil would be a real lottery, since after degrading, in a matter of days or weeks we would lose all the nitrogen provided.

Hence, tools are used today that control or reduce the nitrification process.

We are talking about nitrification inhibitors. 

HOW DO NITRIFICATION INHIBITORS WORK?

Nitrification inhibitors have made a quantum leap in nitrogen management. So much so that, in many areas where the leaching of the nitrate form (NO3-) is high, the mandatory use of nitrification inhibitors has been imposed by law and decreed.

But how do nitrification inhibitors work?

As we have commented before, in a soil the population levels of the nitrosomes and nitrobacter genera , responsible for transforming the ammoniacal form to the nitric form, are not controlled.

Nitrification inhibitors act by reducing said populations, such as a bactericide or bacteriostatic, so that the nitrogen molecule is protected by an agent that reduces this process.

By the time this inhibitor is lost, nitrogen will be transformed into nitric form more quickly, but it will have given time for the crop to develop properly and you will be able to obtain a greater nitrogen reserve in the future.

Although there is a high volume of active ingredients that are used as nitrification inhibitors, these are the most important. Some of them are synthetic (the ones that work best) and some are natural.

NITRIFICATION INHIBITORS, WAXY COATINGS

The mere fact of incorporating a retardant in the release of fertilizers is already a natural way to reduce nitrification when fertilizers are ammoniacal. Bacteria are not in direct contact with nitrogen and will only be able to act when the waxy layer degrades.

Normally it leaves a window of several weeks or even months until the waxy bodies completely release the fertilizer. These are degraded by the action of the direct sun and the water incorporated in the irrigation system or the rain.

In contrast, not only nitrogen is “imprisoned” but other nutritional forms (phosphorus, potassium, sulfur, etc.) are also limited in their absorption if they are inside the waxy ball.

NITRIFICATION INHIBITORS, DMPP AND DCD

These nitrification inhibitors are the most widely used and widely incorporated in a multitude of fields, crops and countries.

3,4DMPP (3,4 3,4 Dimethyl Pyrazole Phosphate) is a patented formula protected by BASF (Germany) and is currently one of the most efficient nitrification inhibitors.

DMPP has the ability to inhibit the growth of bacteria and act as a bactericide.

DCD (dicyandiamide) , another nitrification inhibitor, does not have a bactericidal but a bacteriostatic effect, so it is a way to reduce nitrogen transformation but with less success than DMPP.

In this case, DCD has an effect on nitrosomonas spp. The problem is that it is a fairly soluble element and is easily leached when there is an excess of water (blanket irrigation, rain, etc.).

The first nitrification inhibitor mentioned, DMPP, is relatively immobile by the plant and is not absorbed through the roots, so there is no risk of possible phytotoxicities.

NITRIFICATION INHIBITORS, ORGANIC NITROGEN

Organic nitrogen from organic matter (compost, humic extracts, manure, amino acids, etc.) has the advantage that it is itself a nitrification inhibitor. Not literally speaking, but it is a way of releasing nitrogen slowly as it is transformed into ammonia nitrogen and this into nitric.

The speed with which it does so will depend on the C / N ratio of the soil , which in turn measures the activity of microorganisms that decompose organic matter.

INHIBITION OF UREA TRANSFORMATION

Although it is not part of the nitrification inhibitors , there are also ways to reduce the transformation of urea to the ammonia form.

This transformation usually occurs at breakneck speeds in pH of alkaline soils and in the presence of the  enzyme urease. 

Therefore, the inhibitors are aimed at reducing or limiting the urease enzyme so that said transformation does not occur.

• Triamida N-(n-butil) tiofosfórica (NBPT).
• N- (2-nitrophenyl) phosphoric acid triamide (2-NPT)
• Monocarbamide dihydrogen sulfate (MCDHS)

Among these three urease inhibitors, the first (NBPT) is currently the most widely used, with the ability to keep urea stable for up to 14 days from the time of application.