Nitrogen is an essential mineral for the overall health and optimum growth of plants. Luckily, it’s naturally abundant and can be harvested from many natural sources. It’s also possible to synthesize nitrogen-rich sources inorganically.
Here’s a list of fertilizers high in nitrogen:
- Anhydrous Ammonia
- Ammonium Nitrate
- Urea-Ammonium Nitrate (UAN)
- CAN (Ammonium Nitrate + Limestone)
- Ammonium Sulfate
- Di-ammonium Phosphate
- Calcium Nitrate
- Feather Meal
- Blood Meal
- Cottonseed or Canola Meal
- Alfalfa Meal
- Bone Meal
Some of these materials may be rich in nitrogen but cannot be applied directly into the soil as they may be harmful to the plants. This article will discuss in detail how much nitrogen each fertilizer has, how it can be maximized and safely incorporated into the soil, and the benefits of its other components.
1. Anhydrous Ammonia
Anhydrous ammonia (NH3) contains 82% nitrogen—the highest among commercial fertilizers.
Experts synthesize ammonia by capturing nitrogen from the atmosphere and converting them into anhydrous ammonia through the Haber-Bosch process. Farmers then inject pressurized liquid ammonia into the soil through tractor-drawn knives.
Since anhydrous ammonia readily escapes into the atmosphere, farmers need to inject the fertilizer at least 10 – 20 cm (3.9 – 7.9 inches) deep to prevent immediate loss through evaporation.
Once released into moist soil, ammonia reacts with water and turns into ammonium (NH4), which binds to organic matter. This process reduces the risk of ammonia being leached away in case of heavy water flow. Eventually, the ammonium is converted into nitrates (NO3)—the form which plants can easily absorb.
Meanwhile, gaseous ammonia reacts readily with water, making it dangerous for the human body to absorb. Therefore, farmers must observe correct methods and use appropriate clothing or gear when handling such compounds.
Although ammonia contains the highest amount of nitrogen, it’s not as widely used as urea due to the higher health and environmental risks.
Urea is an essential compound naturally found in the urine of most mammals. Scientists can also synthesize the product in the laboratory through the chemical process called Wöhler Synthesis. This process helped significantly in the mass production of urea.
Many companies produce large amounts of urea annually to meet the high demands in farming as it’s one of the best nitrogen sources. It contains 46% nitrogen and is widely used in animal feeds and fertilizers.
It’s best to add urea to moist soil to initiate a reaction. The compound has to undergo three chemical reactions before the plants can use any of its nitrogen components.
Many plants and microorganisms in the soil contain urease—an enzyme responsible for the breakdown of urea into ammonia. This enzyme requires water to function. In addition, water is also necessary to convert ammonia into ammonium.
Next, the soil microorganisms will convert the ammonium molecules into nitrates that plant roots can easily absorb.
However, it may be important to remember that plants cannot absorb all of the nitrogen present in urea as some of them can be lost in the air naturally because the compound is a volatile substance. It can also lose nitrogen due to high temperatures or high pH in the soil.
Soil temperatures over 80 °F (26 °C) and pH levels above 7.0 may result in faster urea breakdown and nitrogen loss, resulting in reduced nitrogen intake among plants. Temperatures between 45 and 60 °F (7 – 15 °C) and pH levels between 5.0 and 6.0 can effectively delay nitrogen loss through evaporation.
3. Ammonium Nitrate
Ammonium nitrate (NH4NO3) contains 34% nitrogen and is widely used in commercial fertilizers and explosives. While it’s a good source of nitrogen for crops, some countries ban or regulate its distribution due to its high risk of being used for explosives.
Nonetheless, it works great as a fertilizer because the compound’s nitrogen components are equally divided into ammonium and nitrate molecules. The nitrate part is readily available for plants to absorb upon application into the soil. The ammonium provides a nitrogen supplement for a later uptake.
Nitrates are highly water-soluble and are significantly affected by water flow. This property makes it convenient to apply ammonium nitrate through top-dressing and allows for an even distribution of the fertilizer on a wide piece of land.
However, while the nitrogen from nitrates doesn’t dissipate quickly through evaporation, chances are it may be lost through leaching. It’s highly likely during the rainy season in fields or gardens with loose, sandy soil.
Eventually, when the soil dries up, the nitrates stuck beyond the reach of plant roots will be decomposed by soil microorganisms, releasing nitrogen gas that may be lost through the air.
4. Urea-Ammonium Nitrate
Urea-ammonium nitrate is a liquid fertilizer that combines the two compounds and contains 28 – 32% nitrogen. This formulation makes it more convenient to apply the fertilizer along with some herbicides or incorporate it into a foliar spray.
Its liquid form also makes it popular for home gardeners who handle only a few plants. However, it may lead to foliar burn when you apply it directly onto the surface of leaves.
In addition, nitrogen loss is also possible through evaporation or leaching, further reducing the amount of the nutrient that the plant can actually consume.
5. CAN (Ammonium Nitrate + Limestone)
Calcium ammonium nitrate (CAN) is a combination of ammonium nitrate and a calcium source, such as limestone or calcium nitrate Ca(NO3)2. It contains roughly 27% nitrogen and 8% calcium. Half of its nitrogen components come from the nitrate part, and the other half comes from the ammonium.
It is a popular inorganic fertilizer, but its production and distribution are highly regulated since it may be used as an ingredient for explosives.
The calcium component of CAN is beneficial for plants because the nutrient helps provide structural support and functions as a secondary messenger for physically or biochemically stressed plants. Therefore, it’s best to use CAN when plants suffer from both calcium and nitrogen deficiency.
6. Ammonium Sulfate
Ammonium sulfate (NH4)2SO4, also known as AMS, contains 21% nitrogen and is a good source for sulfur, another essential plant nutrient that constitutes 24% of the compound. It comes in dry, granular form, preventing nutrient loss through evaporation.
Like nitrogen, sulfur also helps with chlorophyll formation. It also helps with nitrogen fixation in legumes. Luckily, the sulfate in AMS is readily available for the plants upon application. However, it must be used only when there’s an equal need for nitrogen and sulfur.
One downside of using ammonium sulfate is its high propensity to acidify the soil, requiring farmers or gardeners to routinely check soil pH when using this fertilizer. Therefore, it’s best to use it on moist soil with a high pH level. Otherwise, you may need to employ different ways to elevate the pH more often.
7. Di-Ammonium Phosphate
Di-ammonium phosphate (NH4)2HPO4, sometimes referred to as DAP, is an excellent source of nitrogen and phosphate, which are both essential for plant and root growth. It contains 18% nitrogen and 46% phosphorus.
It is ideal to apply DAP in spring or autumn.
You must also ensure that soil has pH levels between 6.0 and 7.0 because the initial reaction will raise the pH upon application. If the substrate becomes too alkaline, the ammonium molecules will turn into ammonia and dissipate into the air, causing nutrient loss.
Meanwhile, as the ammonium turns into nitrates, the soil will eventually become acidic. Therefore, it is necessary to monitor the soil pH when using this fertilizer.
Human hair contains 15 – 17% nitrogen by volume and also has traces of several other nutrients essential for plants, such as phosphorus, potassium, and magnesium.
Although an excellent nitrogen source, human hair takes several years to decompose entirely, resulting in the slow release of the nutrient for plant use. Therefore, it’s not a good fertilizer by itself that you can apply directly into the soil.
Instead, some people add hair trimmings into compost, where it takes roughly two years to decompose and release nitrogen forms usable by plants. While waiting for decomposition, human hair helps with moisture retention in the compost pile.
Animal hair also contains roughly the same amount of nitrogen by volume and can make a good nitrogen source in your compost.
9. Calcium Nitrate
Calcium nitrate Ca(NO3)2 contains 15% nitrogen from its nitrate part, resulting from the reaction between nitric acid and limestone. This inorganic fertilizer comes in dry, granulated form, making it easier to handle and store. You may need to keep it in a cool, dry place to prevent it from absorbing moisture from the air.
The compound also has the additional benefit of preventing root rot and maintaining overall plant health. This nitrogen-rich fertilizer is best to use when the crops are also suffering from calcium deficiency.
10. Feather Meal
Feather meal is produced by processing the feather by-products from poultry farms. It contains 12 – 15% nitrogen in the form of keratin. This structure makes feather meal ideal as a semi-slow-release nitrogen source.
The feathers are treated with high temperatures of up to 300 °F (149 °C) to denature the proteins, making it easier to break down and release the nitrogen components. In addition, extreme heat makes it possible to break down and turn the feathers into powder form for a more convenient application into the soil.
However, a study showed that residues from numerous pharmaceutical products are still present in feather meal samples regardless of sterilization and heating treatments. These residues may pose serious health risks to humans when we consume plants or animals fed with contaminated feather meals.
11. Blood Meal
A blood meal is a rich, natural source of nitrogen that can be used as fertilizer. It is a by-product from cattle slaughterhouses and has been approved for use as a soil amendment. However, some people find it unethical to apply this fertilizer on crops used to feed livestock.
Since blood meal contains a relatively large amount of nitrogen, constituting 13.5% of its mass, most farmers use it on crops that require high levels of nitrogen, such as leafy vegetables, foliage plants, and flowers.
The product has become so popular that it’s relatively easy to find in many gardening and online stores. If you want to try it on your plants, check out the Burpee Organic Blood Meal Fertilizer (available on Amazon.com). It makes for an excellent organic source of nitrogen and has great reviews.
12. Cottonseed or Canola Meal
Cottonseed or canola meals contain 6 – 7% nitrogen and are potentially good organic fertilizers. They also carry other essential nutrients, such as phosphorus and potassium. These meals are waste products of oilseed processing.
A study showed that plants can efficiently use around 78% of all the nitrogen available in cottonseed or canola meal. However, the mineralization of the nitrogen components in seed meals occurs much slower than in commercial fertilizers, such as ammonium nitrate.
13. Alfalfa Meal
Alfalfa meal makes for a great fertilizer for flowering plants. Although not as much as other commercial fertilizers, the meal contains a decent amount of nitrogen at 3 – 5%. In addition, it also contains phosphorus and potassium.
The meal is prepared by drying alfalfa leaves, grinding them into a finer texture, and letting them ferment. It’s available in pellet form and used as animal feed. Some farmers also found alfalfa meal as a helpful addition to compost to speed up the decomposition of organic materials.
14. Bone Meal
While it’s used as a fertilizer mainly for its high phosphorus content, a bone meal also contains a good amount of nitrogen at 1 – 4%, depending on the source and the manufacturer. Some manufacturers supplement their products with additional nitrogen, raising the value up to 8%.
Bone meal is getting popular for flowering plants, but it’s not recommended for crops that require a large amount of nitrogen. It’s ideal for those with little to no nitrogen deficiency but can still benefit from some supplements.
Cattle manure contains around 0.6 – 4% nitrogen, depending on the source. The nitrogen from manure is generally readily available for plants. In addition, it carries numerous other nutrients, such as phosphorus, sulfur, and zinc, which also contribute to overall plant health.
Some advantages of using manure include its abundance and relatively lower cost than commercially available fertilizers. It also serves as a gentle nitrogen source and packs a significant amount of organic materials to help crops grow more productively.
Moreover, manure helps with moisture retention and prevents runoff, potentially reducing water loss and nutrient unavailability.
Note that when using manure as a fertilizer or an ingredient in compost, it’s best to use manure from livestock, such as cattle and goats because they feed on organic food. Manure from house pets feeding on commercial feeds may contain substances harmful to crops.
Mammalian urine contains nitrogen in the form of urea. Urine from healthy humans generally contains roughly 2% urea. It also contains traces of potassium and phosphorus, which are also primary nutrients required by plants.
The amount or percentage of urea in urine greatly depends on the source’s diet and lifestyle. Under normal conditions, the human body produces 12 – 20 grams of urea every 24 hours. Meanwhile, cattle, sheep, and other mammals release varying amounts of urea in their urine.
However, the urine of house pets feeding on commercial pet food does not make good fertilizer and may even be detrimental to plants due to some ingredients that may be present in the pet food.
If you plan to use urine as a fertilizer or plant additive, it’s best to dilute it in at least ten parts water for every part of the urine. You may need to dilute it in a larger amount of water if it’s too concentrated or has to be applied to young potted plants.
Although urine may seem to be an excellent alternative to expensive commercial fertilizers, it may be difficult to apply frequently as there’s a risk for inconsistency in the concentration of essential nutrients. Urine fertilizer must be used only once a week as a rule of thumb.
This information also clarifies that while urine does provide some nitrogen for plant use, the amount is not enough during the early reproductive and late vegetative stages of plant growth when they need the highest amount of nitrogen.
Compost ideally contains 30 parts carbon for every part nitrogen. The nitrogen values largely depend on the kind of nutrient-rich organic materials added to the pile. Therefore, it’s rather challenging to determine the actual amount of nitrogen present in a pile of compost.
Rough estimates put the value at around 2% nitrogen by the end of the composting process. That said, compost still makes for an excellent soil amendment to provide a good balance of nutrients necessary for healthy plant growth.
This table summarizes these fertilizers rich in nitrogen, in the order of their nitrogen percentage:
|Fertilizer||Percentage / Value|
|Ammonium Nitrate||33 – 34%|
|Urea-Ammonium Nitrate (UAN)||28 – 32%|
|CAN (Ammonium Nitrate + Limestone)||27%|
|Hair||15 – 17%|
|Feather Meal||12 – 15%|
|Cottonseed or Canola Meal||6 – 7%|
|Alfalfa Meal||3 – 5%|
|Bone Meal||1 – 4%|
|Manure||0.6 – 4%|