Nitrogen Fertilizers: making informed choices

Therefore, when fertilization is needed, how do we choose the most appropriate form of Nitrogen to apply? It is not enough to know how much Nitrogen must be supplied: it is also necessary to understand its dynamics in the soil after application.

As always, let’s proceed step by step.

As Nitrogen availability increases, plants tend to produce larger and darker green leaves, which translates into higher photosynthetic capacity and has clearly positive effects on the crop’s vegetative and productive development.

However, when Nitrogen availability exceeds optimal levels, protein synthesis accelerates at the level of the cell plasma, and fewer carbohydrates remain available for the synthesis of calcium pectate, cellulose, etc.—the structural components of the cell wall. Cells tend to increase in size, accumulate more water, and develop thinner walls. This makes the plant more vulnerable to pathogens and insects, as well as to potential mechanical and weather-related damage.

• organic, part of humus, which becomes available for plant uptake through mineralization, in the form of ammoniacal and nitric Nitrogen;
• ammoniacal, weakly available to plants because it is retained by soil clays through adsorption;
• nitrate, highly soluble in water, not retained by clays, and therefore highly available to plants.

Cultivated plants mainly absorb Nitrogen as nitrates dissolved in the soil solution, although these are also highly prone to leaching, with risks of groundwater contamination and consequences for human health, as nitrates are considered potentially carcinogenic.
Losses of Nitrogen from the soil layers explored by crop roots also occur through denitrification (reduction of nitrates/nitrites to gaseous forms such as molecular Nitrogen or nitrous oxide, released into the atmosphere) and volatilization (losses of ammoniacal Nitrogen).

In general, soil Nitrogen originates from atmospheric Nitrogen through two natural processes: biological nitrogen fixation, performed by soil bacteria, and atmospheric nitrogen fixation, caused by electrical discharges that convert molecular Nitrogen into nitrogen oxides and ammonia, later deposited on soil via rainfall. Humans add additional Nitrogen through fertilization.

• Nitrate Nitrogen is the most mobile form in the soil solution and the form most absorbed by plants in aerated soils. It is highly soluble, not retained by the exchange complex, and therefore rapidly available—but also subject to leaching, especially in sandy soils. Once absorbed, it requires metabolic energy to be reduced to ammonium.
• Ammoniacal Nitrogen can be directly absorbed by roots or transformed into nitrate through microbial nitrification. It is partially retained by clay and organic matter, making it less mobile and less available.
• Ureic Nitrogen is not directly absorbable. It is rapidly hydrolyzed by urease—an enzyme of microbial and plant origin—into ammonium and bicarbonate, then follows the nitrification pathway. Urea is among the most widely used mineral Nitrogen sources due to its high concentration (≈46% N) and competitive cost, but if not incorporated into the soil, it is prone to volatilization, especially in alkaline soils and with low rainfall after application.
• Nitrogen from urea-formaldehyde (ureaform) is contained in synthetic condensation products of urea and formaldehyde. It is a slow-release Nitrogen source, where mineral Nitrogen is gradually released by microbial activity, modulated by temperature, moisture, and organic matter content.
• Organic Nitrogen is contained in organic matter compounds (proteins, amino acids, nucleic acids) and becomes available only after microbial mineralization to ammonium and subsequent nitrification. Release efficiency depends on the C/N ratio, humification degree, and ultimately on the organic matrix used in the fertilizer and how it has been processed.

Organic matrices of animal origin

Manure: mixture of animal excreta and bedding material, with variable Nitrogen content. Provides organic matter and secondary nutrients; mineralization speed is medium-slow depending on maturity.

• Nitrate Nitrogen (immediate availability)
• Ammoniacal Nitrogen (rapid–medium availability)
• Ureic Nitrogen (medium availability, after hydrolysis)
• Nitrogen from ureaform (slow release)
• Organic Nitrogen (slow release, variable with matrix)

This parameter alone is not sufficient to evaluate whether a fertilizer meets crop needs in a specific agronomic context. The overall agronomic value of Nitrogen fertilizers must be considered: fast-release forms may have lower efficiency and higher loss risks (leaching, volatilization), whereas slow-release forms, typical of organic and organo-mineral fertilizers, improve nutrient-use efficiency and potentially the overall soil fertility.
The organic matter present in organic and organo-mineral fertilizers not only influences Nitrogen release but also positively affects soil physical and biological properties.

Its organic matter helps maintain soil fertility and protects Nitrogen from volatilization and leaching, improving nutrient efficiency and aligning completely with the “Air Quality Action Plan,” which prohibits urea use in the Po Valley. Agriazoto 300 fully meets the requirements for unrestricted use.

Biodieci is an organic Nitrogen fertilizer obtained by cold pelletizing a balanced blend of four partially hydrolyzed animal protein sources. The size of the organic molecules containing Nitrogen results in gradual release, ensuring extended nutrient availability and minimizing losses of unused Nitrogen units.
Its protein sources define a gradual mineralization curve, beginning with manure and ending with horn meal. Biodieci is designed primarily for organic farming, but is also successfully used in conventional production for topdressing herbaceous and tree crops requiring Nitrogen inputs, ensuring light incorporation to preserve biological activity. It is also an excellent substrate for enhancing soil microbial activity.

Humovegetal 500 is an organic Nitrogen fertilizer based on selected plant matrices, ideal for production systems excluding animal-derived products. It contains exclusive protein-rich plant cakes, abundant in organic Nitrogen, carbon, amino acids, vitamins, and micronutrients.
The organic carbon improves root absorption capacity and overall soil health. It also supports microbial nutrition, mitigates abiotic stress, and enhances nutrient solubility and availability.
The humic acids in Humovegetal 500 stimulate crop growth and improve the efficiency of mineral fertilization thanks to their chelating activity. Its use contributes natural elements that stimulate and revitalize microbial activity and soil fertility within a regenerative agriculture context.