Agricultural urea: properties and applications

Agricultural urea (carbamide, urea, CO(NH₂)₂) is a high-concentration nitrogen mineral fertilizer that occupies a leading position in global crop production. It is a colourless crystalline substance or white (slightly coloured) granules with no odour, readily soluble in water. Urea accounts for about half of all nitrogen applied worldwide, making it a key product in ensuring the yield of cereals, industrial and fodder crops.

Chemical Nature and Agronomic Value

Urea contains 46.2% total nitrogen in amide form — the highest nitrogen content among all solid nitrogen fertilizers. The high concentration of the active ingredient ensures economic efficiency: a tonne of product contains significantly more nitrogen than ammonium nitrate or ammonium sulphate, reducing storage, logistics and application costs.

Nitrogen is a key plant nutrient responsible for vegetative growth, the synthesis of proteins, chlorophyll and enzymes. Urea provides nitrogen to plants over an extended period and is particularly effective for rice and melon crops. Unlike nitrate forms, amide nitrogen is not immediately washed away by precipitation and is gradually transformed in the soil.

Classification, Grades and Standards

Requirements for urea in Russia and CIS countries are regulated by GOST 2081-2010 "Carbamide. Specifications". Depending on the application, the product is produced in two grades:

• Grade A — for industry (production of resins, adhesives, melamine, cyanuric acid and other products).

• Grade B — for agriculture, including private and farm households, as well as for livestock as a feed additive and for retail sale.

Agricultural urea (grade B) is produced in the highest, first and second classes. Key quality indicators for the highest and first classes: mass fraction of nitrogen calculated on a dry basis — not less than 46.2%; mass fraction of biuret — not more than 1.4% (for the second class — not more than 1.5%); mass fraction of total water — not more than 0.5–0.6%; flowability — 100%.

Granulometric composition for the highest class: mass fraction of granules 1 to 4 mm — not less than 94%, 2 to 4 mm — not less than 70%, less than 1 mm — not more than 3%, residue on a 6 mm sieve — absent. Static granule strength — not less than 7 N (0.7 kgf) per granule for the highest class. The granular form ensures good flowability, uniform spreading and reduced dust losses.

Production Technology

Agricultural urea is produced by synthesis from ammonia and carbon dioxide. The process includes the formation of ammonium carbamate at high pressure, its dehydration to produce urea and water, evaporation of the solution, granulation (or prilling) and conditioning of the finished product. To improve physical properties, granules may be treated with anti-caking additives. Modern production facilities ensure high product purity and minimal biuret content — a by-product that in large quantities can inhibit plants.

Application Methods and Agronomy

Basic (pre-sowing) application. Urea is applied to the soil before autumn ploughing or spring treatment. The most important condition for efficiency is immediate incorporation into the soil to a depth of at least 5–6 cm. With surface application without incorporation, nitrogen losses as ammonia gas can reach 15–40% or more, especially on alkaline soils, at high temperatures and after liming. In the soil, urea is hydrolysed by the enzyme urease to ammonium carbonate, which then decomposes with the release of ammonia; further nitrification and denitrification can also lead to losses.

Foliar (leaf) feeding. Urea is one of the few fertilizers suitable for foliar feeding due to its low biuret content and good solubility. Urea solutions (typically 1–5% concentration) are used for feeding cereals, especially wheat, during the growing season. This allows nitrogen deficiency to be quickly corrected and grain quality to be improved.

Irrigation systems. Urea is fully water-soluble and suitable for application with irrigation water through fertigation systems, ensuring precise dosing and uniform nutrient distribution.

Production of fertilizer blends and complex fertilizers. Granular urea is used as a component for preparing blended fertilizers and complex NPK fertilizers.

Reducing Losses and Modern Solutions

To minimize nitrogen losses, urease and nitrification inhibitors are used, as well as coated (polymer) urea forms with controlled release. Studies show that nitrification inhibitors provide yield increases for various crops from 6 to 62%, and urease inhibitors significantly reduce ammonia gas losses and increase nitrogen uptake by plants by 6–13%. Coated urea allows nitrogen release to be synchronized with crop needs, which is especially important for spring wheat and vegetable crops.

Safety and Storage

Urea belongs to substances with low toxicity (hazard class 4) and is non-flammable and explosion-proof. When working with the fertilizer, personal protective equipment (respirator, safety goggles, protective clothing) is recommended to prevent irritation of mucous membranes by dust.

Storage is carried out in closed, well-ventilated warehouse premises protecting the product from atmospheric precipitation and ground water. Urea is hygroscopic, so when moistened it can cake and lose flowability. When storing in bulk, mixing with other types of fertilizers is not allowed. The guaranteed shelf life is 6 months from the date of manufacture; the agronomic shelf life is unlimited. The product is supplied in bulk, in 50 kg bags, and in big bags of 800–1000 kg.

Market and Trends

Global urea production is estimated at 180–190 million tonnes per year, with capacity at 210–220 million tonnes. The largest producers are China (30–35% of global output), India (13–15%), Russia (7–8%) and the USA (5–6%). The Asia-Pacific region dominates consumption, with India and China actively subsidizing fertilizer purchases to support farmers.

Key trends include the growing use of stabilized (inhibited) and coated urea forms to improve nitrogen efficiency and reduce losses, the development of digital precision farming and variable-rate application systems, and tightening environmental requirements for ammonia emissions. Urea remains the most economically accessible and versatile nitrogen source for large farms growing cereals, oilseeds and industrial crops.

Conclusion

Agricultural urea (grade B) remains a key nitrogen fertilizer of global crop production due to its maximum nitrogen content, good solubility and versatility of application. Compliance with agronomic requirements — soil incorporation, use of inhibitors and coated forms — allows its potential to be realized and losses to be minimized. Organising supplies of agricultural urea, including grade and granulometry selection, logistics and financial support, requires an individual approach.