Ammoniacal nitrogen in organic farming: key to yield

What is ammoniacal nitrogen and why is it key in organic farming?

Ammoniacal nitrogen in organic farming is not a product that can be bought and applied directly, but rather the result of a natural process that occurs in the soil when organic matter decomposes. In organic farming, the key to yield lies not in adding mineral ammonium, but in encouraging the soil microbiota to transform organic nitrogen into forms that plants can assimilate, mainly ammonium (NH₄⁺) and nitrate (NO₃⁻). This process, known as mineralisation, is the true driver of nitrogen nutrition in sustainable systems.

European regulations are clear on this point: Regulation (EU) 2018/848 prohibits the use of mineral nitrogen fertilisers in organic production. This means that farmers must rely on organic sources such as composted manure, crop residues, green manures or biostimulants based on microalgae and amino acids. Ammoniacal nitrogen therefore becomes an indicator of soil health and of mineralisation efficiency, rather than an external input.

The importance of this process lies in the fact that ammonium is a form of nitrogen that roots can absorb directly, but it can also be rapidly transformed into nitrate by nitrifying bacteria. The ratio between ammonium and nitrate in the soil affects the uptake of other nutrients, the pH of the rhizosphere and the plant's susceptibility to biotic and abiotic stress. That is why managing the nitrogen cycle in organic farming is a precision task that makes the difference to final yield.

Mechanisms of action: from organic matter to ammonium

Understanding how ammoniacal nitrogen is generated and behaves in the soil is essential for designing an effective organic fertilisation strategy. The process begins with the decomposition of organic matter by heterotrophic microorganisms, which release ammonium through aminisation and ammonification. This ammonium can follow two pathways: being absorbed directly by the roots or being oxidised to nitrate by nitrifying bacteria such as Nitrosomonas and Nitrobacter.

Microbial mineralisation

Mineralisation is the limiting step in most organic soils. It depends on the carbon/nitrogen (C/N) ratio of the organic material applied, as well as on moisture, temperature and aeration. When the C/N ratio is above 25, microorganisms immobilise nitrogen and the available ammonium temporarily decreases. Conversely, with low C/N ratios (below 15), the release of ammonium is rapid but can cause losses through volatilisation if the pH is high.

In soils with low microbial activity, mineralisation slows down and the crop may suffer deficiencies even with abundant organic matter. This is where microalgae biostimulants, such as those developed by Ecoganic, play a crucial role: they provide easily assimilable carbon compounds that stimulate the proliferation of beneficial bacteria and fungi, accelerating the gradual release of ammonium.

Root absorption and rhizosphere effect

Plant roots absorb ammonium through specific transporters (AMT) and nitrate through NRT transporters. Ammonium absorption is more energy-efficient, but its excess can acidify the rhizosphere and compete with the absorption of potassium, calcium and magnesium. This is why, in organic farming, a balance between both forms is sought. Microbial activity in the rhizosphere, stimulated by root exudates and organic biostimulants, favours gradual nitrification that maintains optimal levels of both ions.

Interaction with pH and losses through volatilisation

Ammonium in the soil is in equilibrium with ammonia (NH₃), a gaseous form that is lost to the atmosphere. This equilibrium depends on pH: at pH values above 7.5, the proportion of ammonia increases and volatilisation losses can reach 30 % of the nitrogen applied if it is not properly incorporated. In organic farming, where manures and composts are used, it is essential to apply these materials and incorporate them into the soil or use them in fertigation to minimise losses.

Furthermore, the nitrification of ammonium releases protons (H⁺), which locally acidifies the soil. In calcareous soils, this effect can be beneficial because it improves the availability of micronutrients such as iron and zinc. However, in acid soils, acidification can exacerbate aluminium toxicity. It is therefore recommended to monitor pH and electrical conductivity, and to correct with calcareous amendments when necessary.

Management strategies to enhance ammoniacal nitrogen

To maximise yield in organic farming, it is not enough to supply organic matter; the soil must be managed as a living ecosystem. The strategy should focus on three pillars: increasing available organic matter, stimulating the microbiota and synchronising nitrogen release with crop demand.

Organic amendments and the C/N ratio

The choice of amendment is critical. Mature composts with a C/N ratio between 10 and 15 release ammonium gradually, whereas fresh manures with a high C/N ratio can temporarily immobilise nitrogen. In demanding crops such as organic maize, it is recommended to apply cattle manure compost (C/N 12-15) at a rate of 20-30 t/ha before sowing, incorporating it into the top 15 cm of soil. This provides a sustained release of ammonium throughout the cycle.

Green manures, such as legumes (vetch, broad beans), fix atmospheric nitrogen and incorporate it into the soil. Their decomposition generates ammonium quickly, but if they are incorporated too early, the low C/N ratio can cause excessive release and losses. Ideally, wait until the plant reaches the flowering stage and then incorporate it, when the C/N ratio is more balanced.

Microalgae biostimulants and microbiota

Biostimulants based on Chlorella vulgaris and Scenedesmus provide not only organic nitrogen but also polysaccharides, vitamins and phytohormones that activate the soil microbiota.

Irrigation and aeration management

Mineralisation is an aerobic process; therefore, the soil must have good drainage and oxygenation. Excessive irrigation creates anaerobic conditions that favour denitrification, losing nitrogen as N₂O and N₂. In crops such as organic rice, prolonged flooding reduces ammonium availability and increases gas emissions. Strategies such as intermittent irrigation or dry sowing can mitigate this problem.

In greenhouses, the use of substrates with good porosity and the incorporation of fibrous organic materials (straw, rice husk) improve aeration and microbial activity. Fertigation with organic biostimulants also makes it possible to adjust the ammonium concentration according to the phenological stage, avoiding peaks that could damage the roots.

Rates and timing of application in organic fertilisation

Establishing precise rates for ammoniacal nitrogen in organic farming is complex because it depends on soil mineralisation. However, we can be guided by crop uptake and by the estimated release from amendments. The following table summarises general guidelines based on field experience and on the recommendations of certified organic products.

Crop	N requirement (kg/ha)	Organic amendment	Indicative rate	Timing
Organic maize	180-220	Manure compost	25-30 t/ha	Pre-sowing
Organic tomato	150-200	Vermicompost + microalgae	15-20 t/ha + 3-5 L/ha foliar	Transplanting and flowering
Organic vine	60-80	Compost + green manure	10-15 t/ha	Autumn or spring
Organic olive	80-120	Composted manure	15-20 t/ha	Autumn
Organic citrus	120-160	Compost + fulvic acids	20-25 t/ha + 5 L/ha	Budbreak stage

It is important to remember that these rates are indicative and must be adjusted after a soil and organic matter analysis. Fertigation with microalgae biostimulants, such as those from Ecoganic, allows a split application that synchronises ammonium release with crop demand. For example, in organic tomato, it is recommended to apply 3-5 L/ha of a microalgae biostimulant every 15 days during the flowering and fruit set stage, which maintains optimal ammonium levels in the soil solution.

The phenological timing is crucial. In fruit crops, the greatest nitrogen demand occurs from flowering to fruit swelling. In cereals, from tillering to heading. Applying organic amendments in advance allows mineralisation to release ammonium just when the plant needs it. Foliar biostimulants act as a quick complement, providing amino acids and microalgae that stimulate root uptake and microbial activity.

European regulations: Regulation (EU) 2018/848

Organic production in the European Union is governed by Regulation (EU) 2018/848, which lays down the rules for fertilisation and the use of inputs. This regulation explicitly prohibits the use of mineral nitrogen fertilisers, including those containing synthetic ammonium. Only fertilisers and soil conditioners listed in Annex II of the regulation or authorised by the control bodies are permitted.

The applicable limit for animal manure is 170 kg of nitrogen per hectare per year, a restriction that obliges farmers to supplement with other organic sources and to optimise mineralisation. In addition, inputs must be certified in accordance with the applicable legislation, such as Implementing Regulation (EU) 2021/1165, which lists the authorised substances. It is essential that farmers verify that the products they use have valid certificates specific to their use in organic farming.

In Spain, bodies such as CAAE, Ecocert or Bureau Veritas are responsible for certifying holdings and inputs. However, the certification of a product is not automatic; each input must be assessed by the control body according to its composition and origin. It is therefore advisable to request from the manufacturer the certificate of conformity with Regulation (EU) 2018/848 and with other standards such as NOP USDA or JAS if exporting.

Failure to comply with these rules may result in the loss of organic certification and financial penalties. Therefore, any strategy to enhance ammoniacal nitrogen must be based on authorised inputs and on agronomic practices that respect the environment and soil health.

Frequently asked questions

Can mineral ammoniacal nitrogen be applied in organic farming?

No. Regulation (EU) 2018/848 prohibits the use of mineral nitrogen fertilisers, including those containing synthetic ammonium. Ammoniacal nitrogen must be generated from the mineralisation of organic matter and from authorised inputs.

How can I increase ammoniacal nitrogen in my organic soil?

By encouraging microbial activity with balanced organic amendments (C/N ratio 10-15), maintaining adequate moisture and applying microalgae biostimulants that stimulate the microbiota. Incorporating leguminous green manures is also useful.

What is the difference between ammoniacal nitrogen and organic nitrogen?

Organic nitrogen is the nitrogen that forms part of carbon-based compounds (proteins, amino acids) and is not directly assimilable. Ammoniacal nitrogen (NH₄⁺) is an inorganic form that results from mineralisation and that the plant can absorb. In organic farming, the aim is for organic nitrogen to be transformed into ammoniacal and nitric nitrogen gradually.

How much ammoniacal nitrogen does an organic crop need?

It depends on the crop and the phenological stage. As a reference, the optimal ammonium concentration in the soil solution is usually between 10 and 30 ppm. Ideally, soil and sap analyses should be carried out to adjust fertilisation.

Do microalgae biostimulants provide ammoniacal nitrogen?

Not directly. Microalgae biostimulants provide organic nitrogen and compounds that stimulate the microbiota, which indirectly favours ammonium production. Their effect is more on the efficiency of the nitrogen cycle than on the direct supply of ammonium.