When it comes to picking the right fertilizer for your lawn or garden, nitrogen is one of the most important nutrients to consider. Nitrogen promotes healthy green growth and gives plants their vibrant color. Most fertilizers will have a 3 number analysis on the bag, such as 10-10-10, that tells you the percentage of nitrogen, phosphorous and potassium in the fertilizer. For those looking to maximize nitrogen, the first number is what matters. But which fertilizers offer the highest nitrogen content? Here’s a look at some of the fertilizers with the most nitrogen.
Urea
Urea fertilizer is a dry pellet or granule fertilizer that is over 40% nitrogen. The nitrogen in urea is fast acting and readily available to plants. Urea fertilizer is made from synthesizing ammonia with carbon dioxide. This gives urea the highest nitrogen content of any dry fertilizer. It is a popular choice for giving lawns and gardens a quick nitrogen boost.
Pros of Urea Fertilizer
- Over 40% nitrogen content
- Fast acting nitrogen that is readily available for plant uptake
- Dry pellet form is easy to spread with a broadcast spreader
- Good for quick green up of lawns and providing nitrogen during growth spurts
- Inexpensive per pound of nitrogen compared to other fertilizers
Cons of Urea Fertilizer
- Has a high burn potential if over-applied, which can damage grass and plants
- Nitrogen not in a slow-release form, so can easily leach out of soil
- Needs to be watered in immediately or nitrogen will volatilize into the air
- Contains no phosphorus or potassium, only nitrogen
Ammonium Sulfate
Ammonium sulfate fertilizer is another dry granular fertilizer product that has a high concentration of nitrogen. It is approximately 21% nitrogen in the form of ammonium (NH4+). Ammonium sulfate is created by combing ammonia with sulfuric acid. In addition to having a high nitrogen content, ammonium sulfate also contains 24% sulfur which can benefit certain crops.
Pros of Ammonium Sulfate
- 21% nitrogen content
- Also provides sulfur which some plants need
- Does not volatilize as readily as urea
- Good for acidic soils since it lowers pH
- Low salt index, safe for many plants
Cons of Ammonium Sulfate
- Still has potential to burn plants if over-applied
- Contains no phosphorus or potassium
- Ammonium form of nitrogen not as readily accessible to plants as nitrate nitrogen
- Has to be applied more frequently than slow release nitrogen sources
- Can leach through soil since nitrogen not in slow release form
Calcium Ammonium Nitrate
Calcium ammonium nitrate fertilizer contains both nitrate and ammonium forms of nitrogen for a quick nitrogen boost and longer feeding duration. The nitrogen content of calcium ammonium nitrate ranges from 20-27%, supplying an almost equal ratio of ammonium to nitrate nitrogen. The calcium in this fertilizer also supplies nutrients, helping correct calcium deficiencies.
Pros of Calcium Ammonium Nitrate
- 20-27% nitrogen content
- Balanced and quick availability from the nitrate nitrogen
- Longer duration of nitrogen release from the ammonium
- Added calcium prevents blossom end rot in tomatoes and other vegetables
- Less prone to leaching or volatilization losses
Cons of Calcium Ammonium Nitrate
- More expensive per pound of nitrogen than some other nitrogen fertilizers
- Can still burn plants if over-applied
- Does not contain any potassium or phosphorous
- Calcium content may raise soil pH
Anhydrous Ammonia
Anhydrous ammonia fertilizer is a pressurized liquid form of ammonia that has an extremely high nitrogen content. It is over 80% nitrogen in a liquid form under pressure. This allows more nitrogen to be delivered with less product than other types of nitrogen fertilizers. Anhydrous ammonia must be injected into soil and requires special equipment to apply. It cannot be applied onto the soil surface. Anhydrous ammonia is a popular fertilizer for large field crops like corn and wheat.
Pros of Anhydrous Ammonia
- Over 80% nitrogen content in a liquid form
- Does not leach or volatilize readily once placed into soil
- Small amounts can fertilize large areas
- Cost effective source of nitrogen per pound
Cons of Anhydrous Ammonia
- Requires expensive application equipment and training to apply safely
- Can be hazardous if accidently released
- Must be injected into soil, cannot be broadcast
- Contains no other nutrients besides nitrogen
- Use is not practical for residential lawns or gardens
Liquid Nitrogen Fertilizers
There are a number of nitrogen fertilizers in liquid form that have a high percentage of available nitrogen for plants. While not as concentrated as anhydrous ammonia, liquid nitrogen fertilizers avoid the hazards of using pressurized tanks. Liquid nitrogen fertilizers range from 20-40% nitrogen coming from various sources like urea, ammonium nitrate, ammonium sulfate, or other nitrogen compounds dissolved in water. Popular brands include Urea-Ammonium Nitrate (UAN), Ammonium Polyphosphate (APP), and urea solutions.
Pros of Liquid Nitrogen Fertilizers
- High nitrogen percentage in an easy to apply liquid form
- Avoid hazards of pressurized tanks
- Good for fertigation through irrigation systems
- Can be foliar applied to quickly correct nitrogen deficiencies
Cons of Liquid Nitrogen Fertilizers
- Can leach more readily than slow release forms
- Some urea based forms still subject to volatilization
- Repeat applications needed as nitrogen not in slow release form
- Requires sprayer or irrigation system to apply
Nitrate of Soda
Nitrate of soda, also sometimes called sodium nitrate or Chilean nitrate, is an older dry granular nitrogen fertilizer product that was more widely used in the first half of the 20th century. It has mostly fallen out of favor compared to urea based fertilizers. But nitrate of soda still has relevance for organic growers since it is approved for organic production systems. Nitrate of soda has a nitrogen content around 16%.
Pros of Nitrate of Soda
- Organically approved nitrogen fertilizer
- 16% nitrogen that is in rapid nitrate form
- Dry application through broadcast spreading equipment
- Also supplies sodium which benefits some crops
Cons of Nitrate of Soda
- Lower nitrogen percentage than many alternatives
- Can leach readily since all nitrate form
- Repeated applications needed every 2-4 weeks
- Sodium content can negatively affect soil structure over time
Slow Release Nitrogen Fertilizers
While the fertilizers reviewed so far contain the highest percentages of nitrogen, a downside is the nitrogen is nearly all in a form readily available to plants. For many applications, it is preferable to have some nitrogen in a slow or controlled release form. This provides a longer duration of nitrogen feeding. There are a number of technologies that provide slow release nitrogen.
Polymer Coated Urea
Polymer coated urea products consist of urea granules coated with a polymeric coating. The coating regulates the release of the nitrogen. The nitrogen content of polymer coated urea ranges from 30-40%. The duration of nitrogen release ranges from 30-90 days depending on the thickness of the polymer coating.
Sulfur Coated Urea
Sulfur coated urea is made by coating urea granules with sulfur. The sulfur coating provides a slow release of between 90-120 days. The sulfur coating represents about 10% of the product so nitrogen content ranges from 36-42%. The sulfur also provides soil acidification.
Isobutylidene Diurea
This product provides nitrogen in the form of methylene urea. The methylene urea structure provides a controlled release time of around 4 to 8 weeks. The nitrogen content of isobutylidene diurea is around 31%. It is marketed under trade names like Nutralene and Nitroform.
Ureaformaldehyde
Ureaformaldehyde is polymerization of urea and formaldehyde that forms long chains. These long polymer chains provide a slow release of nitrogen to plants over 60-90 days. Ureaformaldehyde has a nitrogen content of around 38%. It is sold under trade names like N-Sure.
Organic Nitrogen Sources
In organic crop production, synthetic nitrogen fertilizers cannot be used. Growers raising crops organically depend more on cover crops, crop rotation, compost, animal manures and approved natural products to supply nitrogen. Here are some of the fertilizer options approved for organic production with their typical nitrogen percentages:
| Organic Nitrogen Source | Nitrogen Content |
|---|---|
| Blood meal | 12% |
| Fish meal | 10% |
| Feather meal | 12% |
| Alfalfa meal | 2-3% |
| Cottonseed meal | 6-7% |
| Soybean meal | 7% |
| Compost | 1-3% |
| Manure | 1-3% |
The challenge with organic nitrogen sources is they have comparatively low percentages of total nitrogen versus conventional fertilizers. And the nitrogen is nearly all in organic forms that must be broken down by soil bacteria before becoming plant available. This gives a much slower nitrogen release compared to products like urea.
Foliar Nitrogen Fertilizers
Foliar nitrogen fertilizers are liquid fertilizers designed to be sprayed directly on plant leaves and stems. The nutrients are absorbed directly through the epidermis of leaves, bypassing the roots. Foliar nitrogen is mainly beneficial as a rescue treatment if soil nitrogen is deficient during key growth stages. Common foliar nitrogen fertilizers like UAN solution can have 25-40% nitrogen along with other nutrients.
Pros of Foliar Nitrogen Fertilizers
- Rapid way to correct nitrogen deficiencies
- Able to reach plants struggling with poor root uptake
- Good for high value vegetable crops
- Applied only as needed based on plant demand
Cons of Foliar Nitrogen Fertilizers
- Lasts only short term since not taken up by roots and soil
- Can burn leaves if applied too heavily
- Added cost, labor and equipment requirements of spraying
- Not a complete substitute for soil applied nitrogen
Conclusion
There are a number of conventional and organic fertilizer products available with high percentages of nitrogen for those looking to maximize nitrogen nutrition in plants. Products like urea, ammonium sulfate, ammonium nitrate and calcium ammonium nitrate offer the highest nitrogen concentrations in easy to apply dry forms. Slow release nitrogen products reduce leaching while providing longer feeding. And foliar nitrogen fertilizers act as an emergency reserve to quickly correct nitrogen shortages impacting yields. Matching the right nitrogen fertilizer source to your specific crop, soil and situation will provide the best results.
