Ammonium Nitrate Fertilizer – An Overview

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Almost 80 percent of the earth’s atmosphere comprises nitrogen gas. However, it exists in a chemically and biologically unusable form. The importance of Nitrogen has been long identified and realized for plant nutrition. Ammonium nitrate was the first solid nitrogen fertilizer produced on a large scale. It’s been a common Nitrogen source because it contains both nitrate and ammonium. Consequently,  it has a relatively high nutrient content.

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Here, we discuss Ammonium nitrate and its role as an important fertilizer in the agriculture industry.

What is Ammonium Nitrate Fertilizer?

Ammonium nitrate is a chemical compound and is represented with the chemical formula NH4NO3. It is a white crystalline solid consisting of ions of nitrate and ammonium. Ammonium Nitrate is highly soluble in water but is a combustible material (fuel oil). It tends to absorb the moisture from the air, although it does not form hydrates. Tonnes of Ammonium nitrate explosives are manufactures every year. You must have heard about the explosion in Beirut, the Lebanese capital (killed 173 people), recently leading to extensive air pollution.  Large amount of the chemical was stored in a warehouse for six years and forgotten.

Its predominant use in agriculture as a high-nitrogen fertilizer makes it a popular source of Nitrogen after Urea fertilizer. Global production of Ammonium Nitrate stood at 21.6 million tones in 2017.

You can use it as fertilizer to boost the Nitrogen content in the soil. However, its role as an explosive for quarrying and mining is also well known. It acts as an oxidizer and considered relatively safe when there is no contamination and appropriately stored. However, it becomes hazardous if it gets contaminated, mixed with fuel, or stored unsafely.

Commercial Production of Ammonium Nitrate Fertilizer

Post Second World War, the chemical gained popularity as a commercial fertilizer. The production of ammonium nitrate is quite simple. Ammonia gas reacts with nitric acid to form a concentrated solution and considerable heat.

The formation of prilled fertilizer takes place when a drop of concentrated ammonium nitrate solution (95 percent to 99 percent) falls from a tower and solidifies. The low-density prills are more porous than the high-density prills. Consequently, low-density prills are for industrial use. The high-density prills are used as fertilizer. The commercial manufacturers produce granular ammonium nitrate by repeatedly spraying the concentrated solution onto small granules in a rotating drum.

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Ammonium Nitrate solution is produced by neutralizing ammonia with nitric acid under utmost reliable and safe conditions. The most important factors are the neutralization operation and evaporation section under partial vacuum at operating temperatures far below decomposition temperature. Consequently, there is no generation of decomposition products or aerosols. The DCS/ESD system then brings the plant safely before an unsafe situation can occur. Hence, the Ammonium Nitrate Melt is fed into the granulation unit for the production of the final product. The result is solid AN/ CAN granules.

Importance of Ammonium Nitrate Ratio

Nitrogen is known to be the building block of amino acids, proteins, and chlorophyll. Plants can absorb Nitrogen either as Nitrate or Ammonium ions. Consequently, the total uptake of Nitrogen comprises a combination of these two forms.

The ratio between Nitrate and Ammonium is of great significance and affects both plants and soil. For optimal uptake and growth, each plant requires a different ammonium/nitrate ratio. The correct ratio also varies with the temperature and soil properties.

Impact of Temperature on Nitrogen Metabolism

Ammonium metabolism consumes much more Oxygen than the metabolism of Nitrate. Metabolism of Ammonium and its reaction with sugars occurs in the roots. These sugars are delivered from the leaves down to the roots. In comparison, Nitrate transportation takes place up to the leaves. It is reduced to Ammonium, and finally, it reacts with sugars.

Higher temperatures increase the plant’s respiration. It consumes sugars faster, thereby making them less available for the metabolism of Ammonium in the roots. Additionally, at high temperatures, there is a decrease in Oxygen solubility in water. Therefore, making less availability of Oxygen.

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Therefore, the practical conclusion is that applying a lower Ammonium/Nitrate ratio at higher temperatures is advisable. Ammonium nutrition is a more appropriate choice at lower temperatures because Oxygen and sugars are more available at the root level. In addition, since low temperatures restrict Nitrate transport to the leaves, basing the fertilization on Nitrate will delay the plant’s growth.

Storage Concerns of Ammonium Nitrate Fertilizer

It tends to absorb moisture from the air. Consequently, you need to store it in air-conditioned warehouses or sealed bags. The commercial manufacturers usually coat the solid fertilizer with an anti-caking compound to prevent clumping and sticking. Sometimes small quantities of carbonate minerals are added before solidifying. Consequently, this eliminates it’s explosive properties. These additives lower the Nitrogen concentration and are sparingly soluble, making the modified product less suitable for application through an irrigation system (fertigation).

Agricultural Use of Ammonium Nitrate Fertilizer

It is a popular fertilizer as it provides half of the Nitrogen in the nitrate form and half in the form of ammonia. The nitrate form mixes with soil water to the roots, where it’s immediately available for plant uptake. The absorption of ammonium fraction by roots or a gradual conversion to nitrate by soil microorganisms takes place. 

Many vegetable farmers use it because it is an immediately available nitrate source of plant nutrition. Animal farmers use it for hay and pasture fertilization. It is less susceptible to volatilization losses than urea-based fertilizers when left on the soil surface.

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Mixing it with other fertilizers is very common. However, you cannot store these mixtures for extended periods because they tend to absorb the moisture from the air. Ammonium nitrate is highly soluble in water. Thus, it is well suited for creating solutions for fertigation or foliar sprays.

Ammonium Nitrate For Decreased Greenhouse Gas Emissions

Ammonium nitrate (AN) fertilizers are very efficient. They produce less greenhouse gas emissions as compared to other fertilizers. Half of the Nitrogen in it is quick-release Nitrogen which is immediately available to the plants. The other half is slow-release Nitrogen to form an adequate balance in plant nutrition. Calcium ammonium nitrate (CAN) is the most popular straight nitrogen fertilizer in Europe.

CAN is a fertilizer with a nitrogen content of 25 – 28%. It features excellent versatility as it can supply Nitrogen to advance the growth of any plant. Ideally suited to the European acidic soil and colder weather conditions. Consequently, it is the preferred source of plant nutrition for European farmers. it has the lowest carbon footprint per kilogram of product and kilogram nitrogen delivered to the soil among the fertilizers. Thus, CAN helps producers reduce their emissions and enables them to comply with environmental laws and policies.

How to Use Ammonium Nitrate as Fertilizer

While using it in gardens, you should mix it with other compounds. The fertilizer is an instantly useable form of Nitrogen due to its porosity and solubility. It provides Nitrogen from both ammonia and nitrate. The standard method of application is by broadcast spreading the granules. These will rapidly melt in water to allow the Nitrogen to release into the soil.

The application rate is 2/3 to 1 1/3 cup (157.5 – 315 ml.) of amounts of ammonium nitrate fertilizer per 1,000 square feet (93 sq. m.) of land.  Post broadcasting the compound, you should till or water in very thoroughly. The Nitrogen will move quickly through the soil to the roots of the plant for rapid uptake. The most common uses for the fertilizer are in vegetable gardens and in hay and pasture fertilization due to the high nitrogen content.

Advantages and Disadvantages of Ammonium Nitrate Fertilizer

Disadvantages

  • The prolonged use gives an acidifying effect on the soil, thus requiring periodic calcification.
  • Requires a lot of precaution in storage due to its explosive nature.
  • Due to hygroscopic properties, it deteriorates over time, especially in humid environments.
  • It is important to avoid extended storage and damp conditions
  • It is explosive under certain conditions.
  • Due to safety concerns, its storage and use is now highly regulated and restricted sales.

Advantages of Ammonium Nitrate Fertilizer

  • The best source of quick-release nitrogen.
  • A balanced nitrogen nutrition protein provided by Nitrogen in form of ammonium and nitrate.
  • Proven to be very effective for a wide variety of crops
  • Increases the oil content and protein in farmed products
  • Enhances plant growth and provides a ready supply of nitrogen from which plants can draw.

Management Practices

Easy handling and high nutrient content have made it a popular Nitrogen fertilizer. It’s also very soluble in the soil, and the nitrate portion can move beyond the root zone under wet conditions.  The process of denitrification can convert Nitrate to nitrous oxide gas or nitrogen oxides in very wet conditions. Concerns over the illegal use of this fertilizer for explosives have caused strict government regulation in many countries of the world.  Restrictions on sales and transportation have caused some fertilizer dealers to discontinue handling this material.

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Take Away

CAN and AN granules are excellent sources of Nitrogen due to the intelligent nitrogen balance. In addition to fertilization benefits, they are also beneficial for the environment and the soil. It helps producers to reduce their emissions due to the low production emissions. Consequently, they assist the manufacturers in complying with environmental regulations. Complex ammonium nitrate-based NP and NPK fertilizers are multicomponent salt systems prone to high hygroscopicity, caking, and explosive thermal decomposition.

The semi-liquid mixtures used in the production of these fertilizers can also exhibit insufficient thermal stability. One of the most important issues for such slurries is their viscosity, which determines the energy costs for transportation and processing into the final product. Increasing the degree of phosphoric acid ammoniation helps to reduce the ammonium nitrate’s content in the product, but the main question remains about the properties of such fertilizers. 

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