What is Urea? Understanding Its Uses and Benefits in Agriculture

Urea is a white, crystalline organic compound widely used as a nitrogen fertilizer in agriculture due to its high nitrogen content and low cost, which reduces transport and storage expenses. It is neutral in pH, compatible with most soils, and promotes plant growth while also serving as an animal feed additive. Produced by reacting ammonia with carbon dioxide, urea is available in granules or prills, with granules being more efficient due to lower nitrogen loss. Upon application, urea converts to ammonium bicarbonate within 48 hours, and to minimize nitrogen volatilization, it should be incorporated into the soil. Some formulations include urease inhibitors to enhance efficiency and reduce losses.

Urea’s chemical formula is CO(NH2)2, which means it’s made up of one carbon, two nitrogens, four hydrogens, and one oxygen. It’s also known as carbamide.

Urea is highly soluble in water, with a solubility of 108 g/100 ml of water at 20° C.

Urea is a neutral molecule, which makes it suitable for a variety of applications.
Urea is used as a fertilizer because it contains the highest nitrogen content of any industrial chemical. It can be applied to soil or foliage to supply nitrogen to plants. Once in the soil, urea breaks down and converts to nitrate, a plant nutrient. However, urea can also hydrolyze and convert to ammonium and carbon dioxide in the presence of soil moisture and the enzyme urease. This process can happen in two to four days, and it happens more quickly in soils with a high pH. To avoid losing ammonia, urea should be incorporated into the soil during this time, unless it rains.

There are two main types of solid urea fertilizer products:

Prills are small, solid, spherical particles formed by allowing molten urea to solidify into droplets. Typically, urea prills have a diameter between 1-3 mm. The prilling process involves spraying molten urea down a tower, where it hardens into spherical prills as it cools in the air stream. Prills have a relatively high crushing strength and are free-flowing, making them easy to handle and apply.

Granules are larger, solid, cylindrical, or irregularly shaped particles formed by compressing and compacting urea. Urea granules are typically 2-4 mm in diameter. The granulation process involves allowing molten urea to solidify on a rotating drum or pan, which is then crushed, compacted, and sized into granular particles. Granules have a higher bulk density than prills, making them more efficient for certain applications.

The key differences are Shape:

• Prills are spherical, while granules are cylindrical or irregular.
• Size: Prills are slightly smaller, around 1-3 mm, while granules are 2-4 mm.
• Production: Prills are formed by solidifying droplets and granules by compaction.
• Density: Granules have a higher bulk density than prills.

Both prills and granules are widely used as solid urea fertilizers. Prills are often preferred for their ease of handling and application, especially by hand. However, the choice between the two depends on several factors, such as the application method, storage conditions, and specific handling requirements. Understanding these factors is crucial for making the right choice.

Urea is a vital compound synthesized through the reaction of ammonia (NH₃) and carbon dioxide (CO₂) under high temperature and pressure conditions, typically around 200°C. The synthesis occurs in two main phases: initially, ammonia and carbon dioxide react to form ammonium carbamate, as represented by the equation 2NH₃ + CO₂ → NH₄CO₂NH₂. This intermediate then undergoes dehydration to produce urea, illustrated by the reaction NH₄CO₂NH₂ → H₂N−CO−NH₂ + H₂O. The overall reaction is exothermic, releasing heat that aids the subsequent endothermic dehydration process.

The urea synthesis process is carefully controlled, with pressures between 140 and 175 bar promoting the formation of ammonium carbamate, while temperatures of 160 to 190°C are ideal for its conversion to urea. After synthesis, the urea solution is concentrated through evaporation, resulting in solid urea in various forms such as prills, granules, or crystals, which are extensively used in fertilizers and resins. Ammonia for this process is typically produced on-site through natural gas reforming, and the carbon dioxide is often obtained as a byproduct of ammonia production, thereby enhancing the efficiency and sustainability of urea manufacturing.

Urea is primarily used as a nitrogen-release fertilizer due to its high nitrogen content, making it cost-effective for transportation and application. It breaks down in the soil to form ammonium ions, which plants absorb. To enhance efficiency and reduce environmental impact, urea is sometimes modified to create controlled-release fertilizers.

Urea is a key raw material in producing formaldehyde-based resins, such as urea-formaldehyde (UF) resins used in wood-based panels like particleboard and plywood. It is also used in the manufacture of adhesives, plastics, and explosives like urea nitrate.

Urea is widely used in dermatological products for its moisturizing and keratolytic properties. It helps soften dry, rough, or thick skin and is used in treatments for conditions like eczema, psoriasis, and calluses. Urea creams and lotions can contain varying concentrations, with higher concentrations used for more severe skin conditions.

In laboratory settings, urea is used as a protein denaturant and a component of deep eutectic solvents. It can also serve as a hydrogen source for fuel cells and is used in techniques to make brain tissue transparent for imaging purposes.

1. High Nitrogen Content: Urea fertilizer boasts an impressive 46% nitrogen by weight, making it a potent and efficient nitrogen source.
2. Cost-Effective: Compared to other nitrogen sources, urea is budget-friendly, benefiting cost-conscious growers.
3. Versatility: Urea can be used on a wide range of crops, including cereals, vegetables, fruits, and ornamentals. It is compatible with most soil types, making it a popular choice in agriculture.

• Urea contributes to nitrogen runoff, resulting in water pollution and eutrophication, which depletes oxygen and adversely affects aquatic ecosystems.
• Its high solubility in water makes urea susceptible to being washed away by precipitation or irrigation, diminishing its efficacy.
• Improper handling of urea can lead to irritation of the skin, eyes, and respiratory system.
• Urea must be stored at room temperature for several days prior to application, and it may decompose at this temperature, risking nutrient loss.
• Urea provides nitrogen exclusively, lacking other vital nutrients such as phosphorus and potassium essential for optimal plant growth.

To effectively use urea fertilizer, follow these steps:

1. Timing: Apply urea during cool, windless days, ideally in the early morning or late afternoon, to minimize nitrogen loss through volatilization.
2. Soil Testing: Conduct a soil test to determine nutrient deficiencies and the appropriate application rate based on the specific needs of your plants.
3. Application Rate: For most crops, apply about 0.40 to 0.65 lbs. per 100 square feet, or approximately one cup (8 oz.).
4. Preparation: Mix urea with water to create a solution, typically using 1 tablespoon of urea per gallon of water for potted plants. Stir until fully dissolved.
5. Application Method: Apply the solution around the base of the plants, ensuring it doesn’t contact the leaves. For solid urea, broadcast it evenly across the soil, focusing on the root zones
6. Incorporation: Water the soil lightly after application to help the urea penetrate and reach the roots, preventing ammonia gas from escaping. For solid applications, incorporate it into the top inch of soil.
7. Frequency: Reapply every two to four weeks during the growing season, adjusting based on plant needs and soil conditions.

In conclusion, urea is a vital organic compound that plays a crucial role in agriculture as a highly efficient nitrogen fertilizer, promoting healthy plant growth while being cost-effective and adaptable to various soil types. Its production through the reaction of ammonia and carbon dioxide underscores its importance in the agricultural sector, where it significantly contributes to crop yields. Furthermore, the versatility of urea extends beyond agriculture, finding applications in industries such as plastics and resins. As the demand for sustainable agricultural practices continues to rise, urea’s efficiency and effectiveness make it an essential component in meeting global food production needs while minimizing environmental impact.