Nitrogen fertilizers supply plants with nitrogen in usable forms, most commonly as nitrate, ammonium, or urea, to support growth, protein formation, and yield.
Nitrogen drives plant growth like nothing else. It fuels protein formation, chlorophyll production, and overall yield, which is why nitrogen fertilizers are the most widely used crop inputs worldwide. But not all nitrogen fertilizers work the same way. The form of nitrogen — nitrate, ammonium, or urea — determines how fast plants can use it, how easily it moves in soil, and how much you risk losing to the environment. Choosing the right one depends on your crop, soil conditions, and timing.
What Forms Do Nitrogen Fertilizers Come In?
Nitrogen in fertilizers falls into three main chemical forms, each with distinct behavior in soil.
- Nitrate nitrogen (NO₃⁻) is immediately available to plants and moves freely with soil water, which makes it fast-acting but also prone to leaching in wet conditions.
- Ammonium nitrogen (NH₄⁺) is held by soil particles and less mobile, but soil bacteria convert it to nitrate through nitrification — a process that speeds up in warm, well-aerated soil.
- Urea/amide nitrogen must be converted by soil enzymes (urease) to ammonium and then to nitrate before most plants can use it. This takes time and can lose nitrogen to the air as ammonia gas if the urea sits on the surface.
Many products combine forms. For example, UAN (urea ammonium nitrate) liquid fertilizer contains both urea and nitrate, giving a mix of fast and slower-release nitrogen.
Common Nitrogen Fertilizer Products and Their Strengths
Each product has a specific nitrogen content and best-use scenario. The table below shows the main options and what sets them apart.
| Fertilizer | Nitrogen Content | Best Use |
|---|---|---|
| Urea | 46% N | Most concentrated solid N source; requires incorporation or rain to avoid ammonia loss |
| Ammonium nitrate (AN) | 33.5–34.5% N | Top-dressing growing crops; contains both ammonium and nitrate for rapid uptake |
| Anhydrous ammonia | 82% N | Pressurized gas for large-scale field application; slower conversion reduces leaching risk |
| Ammonium sulfate | 21% N | Provides both N and sulfur; good for sulfur-deficient soils |
| UAN (urea ammonium nitrate) | 28–32% N | Liquid fertilizer easy to blend and apply; combines fast and slow-release forms |
| Calcium ammonium nitrate (CAN) | 26–28% N | Safer handling alternative to ammonium nitrate; used on a range of crops |
How to Pick the Right Nitrogen Fertilizer
The 4 Rs — right product, right rate, right time, right place — are the official framework for nitrogen management. Match the form to your crop’s growth stage and your soil. Nitrate-based sources work well for sidedressing growing crops, while urea requires incorporation or rain within a few days to prevent volatilization. Anhydrous ammonia is best injected before planting. Calculate actual N applied by the product’s concentration: 100 pounds of 46% urea delivers 46 pounds of N, while the same weight of 33.5% AN delivers only 33.5 pounds.
If you’re comparing products for your lawn or garden, our tested roundup of the best fertilizers with nitrogen can help you match a product to your specific goals and conditions.
Common mistakes include assuming all nitrogen sources work the same, applying N too early in the season when roots aren’t active, and ignoring soil moisture. A well-drained, warm soil speeds nitrification from ammonium sources; cool, wet soils slow it and may keep ammonium in place longer.
Safety and General Precautions
Anhydrous ammonia requires specialized handling equipment and pressure-rated tanks — it is not a product for casual use. Ammonium nitrate is effective but regulated in many jurisdictions due to security concerns; always follow local laws and supplier guidance when using it. Nitrogen losses through volatilization (as ammonia gas), leaching (nitrate moving below the root zone), and denitrification (conversion to nitrogen gas) all increase when product, timing, or placement is wrong.
FAQs
Is urea the same as ammonium nitrate?
No. Urea (46% N) must convert to ammonium and then nitrate before plants can use most of its nitrogen, while ammonium nitrate (33.5% N) contains both forms and is immediately available. Urea also loses nitrogen to the air more easily if left on the soil surface without incorporation.
Can I use liquid nitrogen fertilizer on my lawn?
Yes. UAN liquid fertilizer (28% or 32% N) works on turf, but you must apply it at the correct dilution rate and water it in to prevent leaf burn. Always follow the product label for application rates specific to lawn use.
What causes nitrogen fertilizer to smell like ammonia?
A strong ammonia smell usually means nitrogen is being lost as ammonia gas — common when urea or UAN is applied to warm, dry soil without incorporation or rainfall. This volatilization reduces the nitrogen available to plants and can waste much of the application.
References & Sources
- Purdue Extension. “Nitrogen Fertilizers — An Overview.” Covers nitrogen forms, products, and best-use guidance.
- Michigan State University Extension. “Selecting Forms of Nitrogen Fertilizer.” Explains behavior of nitrate, ammonium, and urea in soil.
- Crop Nutrition (IPNI). “The Facts: Nitrogen Fertilizer.” Details the production chain from ammonia to downstream products.