Nitrogen fertilisers: types, application rates and key considerations for effective use

Most crops cannot use atmospheric nitrogen directly. They require nitrogen in the form of mineral compounds that enter the soil through fertilisers. Agricultural producers need to understand how nitrogen-containing products work in order to achieve a genuinely high-quality yield. In particular, it is important to understand that a nitrogen fertiliser is not a universal nutrient input that can be applied at will, but a substance that should be used according to specific recommendations.

What are nitrogen fertilisers and why are they needed?

Nitrogen fertilisers are organic or inorganic substances that contain a key nutrient in forms available to plants: ammonium, nitrate or amide forms. Nitrogen is an essential component of proteins, enzymes and nucleic acids. To properly assess its role in crop growth and development, it is worth considering the following aspects:

• Photosynthesis and chlorophyll. Nitrogen is a direct component of chlorophyll, the green pigment responsible for converting solar energy into organic matter.
• Protein synthesis. As a key component of amino acids, nitrogen supports the formation of plant proteins and affects the gluten content in wheat.
• Vegetative development. This element stimulates the intensive growth of leaves and shoots, allowing the crop to quickly form a strong assimilative apparatus.

A sufficient amount of nitrogen improves the uptake of phosphorus and microelements, helping to create balanced plant nutrition.

How to determine whether a plant needs nitrogen

Before looking for the most common nitrogen fertilisers, it is worth understanding the first signs that indicate a deficiency. Since the role of nitrogen in plant nutrition is to support growth, and nitrogen compounds are mobile, when nitrogen is lacking the plant begins to “draw” reserves from older leaves. The following signs may indicate this:

• Colour change. The first sign is usually paling of the leaves.
• Growth inhibition. Crops appear weakened and suppressed.
• Reduced leaf area. Leaf blades become smaller.

Visual diagnosis should be confirmed by laboratory soil analysis or plant tissue diagnostics, as similar symptoms may sometimes be caused by drought.

What types of nitrogen-containing fertilisers are there?

Each type available on the market has its own specific properties, speed of action and effect on soil acidity.

Carbamide / urea

This is the most concentrated solid nitrogen fertiliser, containing 46% nitrogen. It contains nitrogen in amide form, which is gradually converted into plant-available forms.

Ammonium sulphate

Ammonium sulphate contains 21% nitrogen and 24% sulphur. It is a physiologically acidic fertiliser, making it particularly suitable for alkaline soils. The presence of sulphur improves nitrogen uptake by plants.

Ammonium nitrate

When considering the different types of nitrogen fertilisers, ammonium nitrate is important to mention. It is a versatile product with a nitrogen content of 34%. It contains both nitrate nitrogen, which acts quickly, and ammonium nitrogen, which has a prolonged effect. This makes it especially useful for the early spring “start” of winter crops.

Sodium nitrate

Sodium nitrate contains 16% nitrogen. It is an alkaline fertiliser, so its use is appropriate on acidic soils. Sodium has a positive effect on the sugar content of beet crops.

Calcium nitrate

The classification of nitrogen fertilisers also includes calcium nitrate. It consists of 15.5% nitrogen and calcium. This fertiliser is particularly valuable for high-quality nutrition of tomatoes and peppers, as it helps prevent blossom-end rot and strengthens plant cells.

Potassium nitrate

This group includes compound fertilisers containing 13% nitrogen and 46% potassium. Potassium nitrate is especially useful at the flowering stage and helps increase plant resistance to drought.

Methods for applying nitrogen fertilisers and how to choose them

The effectiveness of fertilisation directly depends on the method used to apply nitrogen nutrition to the field. Incorrect application may lead to a significant part of the active substance simply being lost through volatilisation.

• Basal application. This is carried out in spring before or during soil cultivation, creating a foundation for root development.
• Pre-sowing application. Adding small doses to planting holes or rows provides energy for germination.
• Fertigation. Nitrogen fertiliser is supplied in portions through the irrigation system, allowing nutrient supply to be controlled in real time.

Foliar application helps plants recover more quickly from stress during adverse weather conditions.

When to apply nitrogen fertilisers: application rates

Once the agricultural laboratory has provided its conclusion, fertiliser application can begin. Select nitrogen fertilisers, with the type recommended by specialists where necessary, in the amount required to cover the identified deficiency. Application timing correlates with crop development stages. Spring is the period for an active start, summer supports vegetation, and autumn is used to prepare winter crops. Indicative application rates in kg/ha are: sunflower, 80-120; maize, 120-180; wheat, 60-80. It is important to remember that excess nitrogen is just as dangerous as deficiency.

Application specifics for different crop types

After determining which fertilisers contain nitrogen, it is possible to move on to studying application methods. What works for one crop may not be suitable for another. For example, for potatoes, nitrogen is applied in rows during planting. For spring wheat, the tillering stage is critical. Winter wheat, however, requires split application: the first dose is applied on frozen-thawed soil, and the second at the stem elongation stage.

Benefits and risks of using nitrogen fertilisers

Every agrotechnical decision has its advantages and certain drawbacks that should be understood in advance. The main benefits of nitrogen nutrition include:

• Plant resilience. Healthy plants are better able to withstand pathogens and pests.
• Yield. An optimal nitrogen dose supports stable biomass growth.
• Quality. The protein and vitamin content of produce improves.

The main risks appear in cases of overapplication. This can lead to soil acidification and the accumulation of harmful nitrates in produce. In addition, plants overfed with nitrogen become an easier target for fungal diseases: their resilience weakens and they become more vulnerable to disease.

However, it is important not to forget that fertiliser analysis before application is essential, as low-quality counterfeit products unfortunately do occur on the market.

Therefore, nitrogen fertilisers are a powerful tool that, when used responsibly, can help achieve high yields, but they require accurate calculation and laboratory control.