Urea Ammonium Nitrate (UAN) is a widely utilized liquid nitrogen fertilizer in modern agriculture, known for its high concentration and ease of application. It is a non-pressurized solution used to supply crops with the nitrogen necessary for growth and yield development. Farmers value UAN for its flexibility, as it can be applied efficiently through various equipment and blended with other plant nutrients. This versatile product has become a standard choice for nutrient management programs.
What Makes Up Urea Ammonium Nitrate?
UAN fertilizer is an aqueous solution created by dissolving two distinct nitrogen sources, urea and ammonium nitrate, into water. The most common commercial product is UAN-32, which indicates a concentration of 32% total nitrogen by weight; grades like UAN-28 and UAN-30 are also available. This high concentration is a significant factor in the product’s efficiency and popularity in large-scale farming operations.
The nitrogen content in UAN-32 is split into three separate forms. Approximately 50% of the nitrogen originates from urea, while the remaining 50% comes from the ammonium nitrate component. The ammonium nitrate immediately dissociates in the solution, yielding both ammonium ions (NH4+) and nitrate ions (NO3-). Therefore, the final UAN solution contains a balance of three distinct nitrogen forms: urea, ammonium, and nitrate.
The Advantage of Three Nitrogen Forms
The effectiveness of UAN fertilizer stems from its tri-form nitrogen composition, which provides plants with nutrient availability across different timeframes. This staggered release mechanism ensures that crops receive an immediate nitrogen boost and a sustained supply throughout their growth cycle.
The nitrate portion (NO3-), which constitutes about 25% of the total nitrogen, is immediately available for plant uptake. Since it is negatively charged, nitrate does not bind to soil particles and moves freely with soil water, allowing for rapid assimilation by plant roots.
The ammonium portion (NH4+), representing another 25% of the total nitrogen, provides a slightly longer-term source of nutrition. Ammonium ions are positively charged, causing them to temporarily bind to the negatively charged clay and organic matter particles in the soil. This binding prevents immediate loss through leaching until soil microbes begin the process of nitrification.
The remaining 50% of the nitrogen is urea, which represents the longest-lasting supply. Before plants can utilize urea, it must undergo hydrolysis, where the urease enzyme converts the urea into ammonium. This process takes between two and ten days following application. This newly formed ammonium then provides a medium-term source before being converted to nitrate by soil bacteria. This balanced delivery minimizes the risk of nutrient deficiency periods compared to single-source nitrogen products.
Safe Storage and Application Guidelines
Handling UAN fertilizer requires adherence to specific safety and storage guidelines due to its chemical properties. The solution is corrosive to mild steel, so storage tanks and application equipment must be constructed from or lined with corrosion-resistant materials, such as stainless steel or fiberglass. Manufacturers typically add corrosion inhibitors to the final product to help protect metal equipment and storage infrastructure.
Temperature control is a primary concern for storing UAN, especially for the higher concentration grades. UAN-32 has a “salt-out” temperature of approximately 32°F (-2°C). If the temperature drops below this point, the dissolved salts, urea, and ammonium nitrate, will begin to crystallize out of the solution. This crystallization can clog application equipment and reduce the fertilizer’s effectiveness. UAN-28 is often preferred in regions with colder winter temperatures, as its salt-out temperature is significantly lower.
During application, UAN’s liquid nature allows for high versatility, including:
- Direct soil injection.
- Broadcast spraying onto the soil surface.
- Delivery through irrigation systems.
- Use in “weed and feed” programs because of its compatibility with many herbicides.
Equipment used for application, such as spray lines and nozzles, must be thoroughly flushed with water after each use to prevent the formation of crystals that could cause blockages or corrosion. When mixing UAN with other chemicals, a small-scale compatibility test is always recommended, as certain combinations can result in the formation of insoluble precipitates that damage equipment. Personal protective equipment, including gloves and eye protection, should be worn when handling the liquid. Storing UAN in a secure, cool location, away from incompatible substances like strong acids or alkalis, helps maintain its quality and ensures handler safety.