Ammonium nitrate is one of the most widely produced chemicals in the world, and its primary use is straightforward: it feeds crops. As a nitrogen-rich fertilizer, it supplies the nutrient most essential to plant growth in a form that soil can absorb readily. But the same chemical energy that makes it valuable in agriculture also makes it useful as an industrial explosive, a cold-pack ingredient, and even a candidate rocket propellant. That range of applications, paired with its well-known explosive hazard, gives ammonium nitrate a complicated reputation that is worth understanding in detail.
Fertilizer and Crop Production
Agriculture is by far the largest consumer of ammonium nitrate. The compound contains about 34% nitrogen by weight, split between two chemical forms: ammonium and nitrate. Plants can take up both, which means ammonium nitrate delivers a quick nutrient boost compared with fertilizers that must first be converted by soil bacteria before crops can use them. Farmers value it for cereals, pastures, and other crops that need a fast supply of nitrogen during the growing season.
One practical advantage over urea, the world’s most commonly used nitrogen fertilizer, is lower ammonia loss to the atmosphere. When urea is spread on the soil surface, a significant share of its nitrogen escapes as ammonia gas before plants can absorb it. A global synthesis of ammonia-volatilization studies found that switching to calcium ammonium nitrate or similar alternatives reduced those losses by roughly 22 to 55% compared with urea.1ScienceDirect. Ammonia volatilization from synthetic fertilizers and its mitigation strategies: A global synthesis That difference matters both for farm economics and for air quality, since ammonia contributes to fine particulate pollution.
In manufacturing, the compound is made by reacting ammonia with nitric acid. A typical two-stage process first produces an 80% ammonium nitrate solution, which is then concentrated to about 99.7% in vacuum evaporators before being shaped into the familiar white granules or prills that farmers spread on fields.2Heliyon. A novel industrial-scale strategy to prevent degradation and caking of ammonium nitrate The prilled form dissolves easily in soil moisture, making the nitrogen available to roots within days of application.
Mining and Industrial Blasting
The second-largest use of ammonium nitrate is as the oxidizer in commercial explosives, especially in mining and quarrying. When mixed with fuel oil, it forms ammonium nitrate–fuel oil, or ANFO, one of the most widely used civilian explosives in the world.3PubMed Central. Improving ANFO: Effect of Additives and Ammonium Nitrate Morphology on Detonation Parameters The appeal is simple: ANFO is cheap and easy to prepare on site. Workers load porous ammonium nitrate prills into boreholes drilled into rock, soak them with diesel fuel, and detonate with a booster charge.
ANFO does have limitations. It performs poorly in wet conditions because ammonium nitrate dissolves in water, and it sometimes detonates at less than ideal efficiency, which can leave unreacted material behind.3PubMed Central. Improving ANFO: Effect of Additives and Ammonium Nitrate Morphology on Detonation Parameters Researchers have explored various ways to improve performance, including partially substituting ammonium nitrate with more energetic compounds like nitromethane. Small additions of nitromethane can raise blast strength without meaningfully changing the mixture’s resistance to accidental ignition from friction, though sensitivity to impact does increase somewhat.4Scientific Reports. Evaluation of the ammonium nitrate fuel oil-nitromethane energetic material sensitivity
For wetter environments, the mining industry relies on emulsion explosives instead. These are water-in-oil mixtures where a concentrated ammonium nitrate solution is dispersed as tiny droplets within an oil phase. The oil coating gives them good water resistance, and studies show they maintain performance even after days of contact with water.5REM, International Engineering Journal. Open-access Guide for stability evaluation of ammonium nitrate-based emulsions Between ANFO and emulsions, ammonium nitrate-based products dominate the global commercial explosives market.
Instant Cold Packs
If you have ever squeezed an instant cold pack from a first-aid kit, you have used ammonium nitrate. Inside the pouch, a thin inner bag of water sits surrounded by dry ammonium nitrate crystals. When you break the inner bag by squeezing, the salt dissolves in the water, and the temperature drops sharply. This happens because the dissolution is endothermic, meaning it absorbs heat from its surroundings rather than releasing it.6Journal of Membrane Science. Membrane distillation crystallization of ammonium nitrate solutions to enable sustainable cold storage: Electrical conductivity as an in-situ saturation indicator
The temperature drop is large enough to relieve pain and reduce swelling from sprains and bruises, which is why these packs are standard in athletic training rooms and ambulances. The same endothermic property has also attracted interest for larger-scale cold-storage applications, where researchers are exploring ways to crystallize the dissolved ammonium nitrate back out so the cycle can be repeated, turning a single-use cold pack concept into a reusable cooling system.6Journal of Membrane Science. Membrane distillation crystallization of ammonium nitrate solutions to enable sustainable cold storage: Electrical conductivity as an in-situ saturation indicator
Rocket Propellant Research
Ammonium nitrate has long attracted attention as a potential oxidizer for solid rocket fuel, mainly because it is cheap and burns cleanly. Unlike ammonium perchlorate, the oxidizer most commonly used in large solid rockets, ammonium nitrate produces no chlorine-containing exhaust gases, making it much more environmentally friendly. It also generates no visible smoke plume, which has obvious appeal for military applications where stealth matters.7Journal of Hazardous Materials. Ammonium nitrate: a promising rocket propellant oxidizer
The problem is performance. Ammonium nitrate burns slowly and releases less energy per gram than ammonium perchlorate. It is also hygroscopic, meaning it absorbs moisture from the air, and it undergoes a crystal-structure change near room temperature that causes it to expand and contract. Over time, that expansion crumbles the propellant grain and can lead to unpredictable burning.7Journal of Hazardous Materials. Ammonium nitrate: a promising rocket propellant oxidizer Researchers have worked on stabilizing additives and modified formulations to overcome these drawbacks, but for large rocket motors, ammonium perchlorate remains the industry standard. Ammonium nitrate has found more traction in gas generators and smaller propulsion systems where its clean exhaust outweighs the energy penalty.
Why Ammonium Nitrate Explodes
Ammonium nitrate by itself is not classified as an explosive. Under normal conditions it is a stable white solid that you can handle, pile, and transport without special precautions. The danger arises when it is heated to high temperatures or contaminated with certain materials, at which point decomposition can accelerate into a self-sustaining reaction that releases enormous volumes of gas almost instantaneously.
The chemistry behind the hazard involves nitrous acid, a short-lived intermediate that forms as ammonium nitrate breaks down. Researchers studying the decomposition process have observed that nitric oxide gas builds up during an induction period, then reacts with oxygen in the air to produce the brown nitrogen dioxide fumes visible in ammonium nitrate fires. A key finding is that nitrous acid acts as a catalyst, driving the reaction faster in a feedback loop. Removing nitric oxide from the gas phase, or adding a base to neutralize the acid, can slow or stop the runaway decomposition.8Journal of Environmental Chemical Engineering. The mechanism of the spontaneous detonation of ammonium nitrate in reactive grounds
Contamination makes things worse. Chloride salts, for example, lower the energy barrier for decomposition and make the reaction release more heat. Experimental work on ammonium nitrate mixed with potassium chloride confirmed that chlorine radicals open up additional decomposition pathways that are more energetic than the compound’s normal breakdown routes.9PubMed. Mechanism study of ammonium nitrate decomposition with chloride impurity using experimental and molecular simulation approach Iron sulfide minerals like pyrite have a similar effect: their presence lowers the critical temperature at which ammonium nitrate can undergo thermal explosion, meaning a stockpile contaminated with iron-sulfide-bearing rock could detonate at temperatures that pure ammonium nitrate would survive without incident.10PubMed. Thermal stability and kinetics of decomposition of ammonium nitrate in the presence of pyrite
Major Disasters and Regulatory Gaps
The explosive potential of ammonium nitrate has been demonstrated catastrophically multiple times. The 2020 Beirut port explosion, caused by roughly 2,750 tonnes of improperly stored ammonium nitrate, killed over 200 people and destroyed much of the city’s harbor district. A historical review of such incidents found a clear pattern: most large ammonium nitrate explosions result not from the material’s inherent instability but from inadequate control of storage conditions, typically a fire in or near the storage structure that heats the stockpile past the point of no return.11Process Safety Progress. Historical record of ammonium nitrate disasters
The 2013 explosion at the West Fertilizer Company in Texas illustrated a different regulatory failure. Analysis of that disaster identified gaps between the regulations on the books and the oversight actually applied to small fertilizer storage facilities. Technologies that could make ammonium nitrate less likely to explode, or that could reduce the severity of an explosion if one occurs, already exist but were not required at the site.12Fire and Materials. The ammonium nitrate explosion at West, Texas: A disaster that could have been avoided The federal review that followed recommended tighter reporting requirements and better coordination between chemical safety, environmental, and homeland security agencies.13ScienceDirect. Case study and lessons learned from the ammonium nitrate explosion at the West Fertilizer facility
These events have pushed many countries to restrict how ammonium nitrate can be stored and who can buy it in bulk. Some jurisdictions require it to be kept away from combustible materials, stored in fireproof buildings, and inventoried regularly. Others limit retail sales of pure ammonium nitrate and instead require diluted or chemically modified formulations that are harder to detonate.
Storage and Handling Challenges
Even when explosion is not a concern, storing ammonium nitrate is trickier than storing most other fertilizers. The compound is hygroscopic, meaning it pulls moisture from humid air. Once it absorbs enough water, the granules soften, stick together, and eventually harden into a solid cake that is difficult to spread on a field. That caking problem has plagued manufacturers for decades.
Industrial-scale approaches to fighting caking include coating the prills with additives that reduce moisture absorption. One study tested silicic acid, calcium lignosulfonate, and sodium silicate as anti-caking agents during the production process and found they reduced hygroscopicity. Degradation was still observed after two years of storage, which the European Fertilizer Manufacturers Association considers the standard benchmark for shelf life.2Heliyon. A novel industrial-scale strategy to prevent degradation and caking of ammonium nitrate For farmers, the practical advice is simple: keep bags sealed, store them off the ground in a dry area, and use older stock first.
The crystal-structure transition mentioned earlier in the context of rocket propellants is another storage headache. As temperature cycles above and below about 32 °C, ammonium nitrate crystals shift between different internal arrangements. Each shift changes the volume of the crystal slightly, which over many cycles cracks prills apart into dust. In warm climates where day-night temperature swings are large, this can turn a bag of clean granules into a pile of powder within a single season.
Environmental Concerns From Agricultural Use
When ammonium nitrate fertilizer is applied to fields, not all of the nitrogen ends up in the crop. Some is lost as gas (ammonia or nitrous oxide), and some leaches through the soil as nitrate and enters groundwater or surface water. A global meta-analysis of field data from hundreds of sites found that the fraction of applied nitrogen that leaches as nitrate is not fixed. Instead, it increases as application rates go up, meaning that each additional kilogram of fertilizer is proportionally more likely to end up in the water supply rather than in the plant.14ScienceDirect. Estimating soil nitrate leaching of nitrogen fertilizer from global meta-analysis
Excess nitrate in water bodies fuels algal blooms, a process called eutrophication. When those blooms die and decompose, they consume dissolved oxygen, creating dead zones where fish and other aquatic life cannot survive.15Journal of Applied Sciences Research and Journal. Effect of Losing Nitrogen Fertilizers on Living Organism and Ecosystem, and Prevention Approaches of their Harmful Effect The Gulf of Mexico dead zone, fed largely by nitrogen runoff from Midwestern farmland, is the most visible example, but the problem exists wherever intensive agriculture meets downstream waterways.
Nitrate contamination of drinking-water wells is also a health concern in agricultural regions. High nitrate levels in drinking water have been linked to a blood disorder in infants and are being studied for potential connections to certain cancers in adults. For these reasons, best practices in farming emphasize applying no more fertilizer than the crop can actually use, timing applications to coincide with peak plant demand, and using cover crops or buffer strips to intercept runoff before it reaches streams.
Calcium Ammonium Nitrate and Diluted Formulations
Because of both the safety and environmental concerns around pure ammonium nitrate, many markets have shifted toward blended products. Calcium ammonium nitrate, or CAN, is the most common alternative. It mixes ammonium nitrate with calcium carbonate (essentially ground limestone), which dilutes the nitrogen content to around 27% and makes the product much harder to detonate. CAN also has lower ammonia volatilization losses than urea, as noted above, and the calcium component can benefit acidic soils.
In some countries, pure ammonium nitrate fertilizer has been effectively banned from retail sale to the general public. Australia, for example, tightly restricts access to fertilizer-grade ammonium nitrate because of its potential misuse in improvised explosives. In those markets, CAN or urea-ammonium nitrate solutions serve as functional substitutes for most agricultural needs. The trade-off is that farmers may need to apply more product per hectare to deliver the same amount of nitrogen, which slightly raises transport and spreading costs.
Other formulations add ammonium sulfate or potassium to create multi-nutrient blends. These are designed not only to reduce detonation risk but also to supply sulfur or potassium alongside nitrogen, simplifying the farmer’s fertilizer program. The trend in the fertilizer industry is clearly toward products that deliver ammonium nitrate’s agronomic benefits while minimizing its storage and security liabilities.
How Ammonium Nitrate Differs From Other Common Fertilizers
Farmers choosing a nitrogen source are essentially picking among trade-offs. Urea is the cheapest per unit of nitrogen and the most widely traded globally, but it loses a large share of its nitrogen as ammonia gas when surface-applied, and it needs soil enzymes to convert it into a plant-available form, which delays nutrient uptake. Ammonium sulfate provides sulfur alongside nitrogen and works well on alkaline soils, but its nitrogen content is lower at about 21%, meaning more product is needed per hectare. Anhydrous ammonia, a pressurized gas injected directly into soil, is the most concentrated nitrogen source at 82% nitrogen, but it requires specialized equipment and is dangerous to handle.
Ammonium nitrate sits in the middle of these trade-offs: moderate nitrogen concentration, immediate availability to plants, lower volatilization losses than urea, but higher cost and regulatory burden. Where it once dominated nitrogen fertilizer markets in the mid-twentieth century, it has gradually lost ground to urea and urea-ammonium nitrate solutions in many regions, driven by urea’s lower cost and by increasing restrictions on ammonium nitrate sales. In parts of Europe and the former Soviet Union, ammonium nitrate and CAN remain the fertilizers of choice, partly out of agronomic tradition and partly because cooler climates reduce the volatilization advantage of urea.
For specialty applications like greenhouse growing or fertigation (injecting fertilizer through irrigation lines), ammonium nitrate’s high solubility is a distinct advantage. It dissolves cleanly and does not leave the residue that some other fertilizers can leave in drip-irrigation emitters. Growers who need precise, fast-acting nitrogen delivery often consider it the superior product despite its higher price point and tighter handling requirements.