Ammonium nitrate is a synthetic nitrogen fertilizer with the chemical formula NH₄NO₃, containing between 33 and 34 percent nitrogen by weight. That makes it one of the most nitrogen-dense fertilizers available, and nitrogen is the nutrient crops consume in the largest quantities. It’s sold as small white pellets or granules and dissolves readily in water, which is part of what makes it so effective in the field.
Why the Nitrogen Content Matters
Nitrogen drives leaf growth, chlorophyll production, and protein synthesis in plants. Ammonium nitrate delivers 34 percent nitrogen, compared to 46 percent for urea and 21 percent for ammonium sulfate. But the raw percentage doesn’t tell the whole story. What sets ammonium nitrate apart is the form of nitrogen it provides.
Each molecule contains two types of nitrogen: ammonium (NH₄⁺) and nitrate (NO₃⁻). Plants can absorb both forms, but they use them differently. Nitrate is immediately available for root uptake and moves freely through soil water. Ammonium binds to soil particles and releases more gradually. This dual delivery means crops get a quick initial feeding from the nitrate half plus a slower, steadier supply from the ammonium half.
Research has shown that supplying both forms of nitrogen together outperforms either one alone. Plants receiving a balanced mix show better nitrogen absorption, improved photosynthetic efficiency, and more stable soil pH around the root zone. A large meta-analysis of crop studies found that wheat grown with a 50:50 ratio of ammonium to nitrate increased biomass by 13.3 percent and protein content by 7.1 percent compared to nitrate-only feeding. Rice responded best to a 75:25 ammonium-to-nitrate ratio, gaining 26 percent more biomass and nearly 22 percent more chlorophyll than with ammonium alone.
How It Compares to Urea
Urea is the other dominant nitrogen fertilizer on the market, and it’s typically cheaper per ton. But urea has a significant drawback: it loses nitrogen to the air through a process called volatilization. When urea granules sit on the soil surface, enzymes break them down and release ammonia gas. In one study on alkaline soils, urea lost up to 7.8 percent of its applied nitrogen as ammonia within just 14 days. Ammonium nitrate showed significantly lower ammonia losses under the same conditions.
That difference matters for both your wallet and the environment. Less volatilization means more of the nitrogen you paid for actually reaches the plant. It also means less ammonia drifting into the atmosphere, where it contributes to fine particulate pollution and acid deposition.
How It’s Made
The manufacturing process starts with a straightforward chemical reaction: ammonia plus nitric acid produces ammonium nitrate in solution. This happens in a vessel called a neutralizer, and the resulting liquid is then concentrated by evaporation until it contains 95 to 99.8 percent ammonium nitrate at roughly 300°F.
From there, the concentrated melt is turned into a solid product through one of two main methods. In prilling, the hot liquid is sprayed from the top of a tall tower. As droplets fall through rising cool air, they solidify into small, nearly spherical pellets called prills. In granulation, the melt is sprayed onto tiny seed particles tumbling inside a rotating drum. Layer after layer builds up on each seed, producing larger, denser granules.
The finished product is then cooled, screened for size, and coated with materials like clay or diatomaceous earth. That coating prevents the granules from clumping together during storage and shipping, since ammonium nitrate readily absorbs moisture from the air.
Prills vs. Granules
Prills are lighter and more porous, which makes them dissolve faster in soil moisture. They work well for immediate application but can be more fragile during handling. Granules are denser and harder, so they hold up better in mechanical spreaders and can be blended more easily with other fertilizer components like phosphorus and potassium. Most modern agricultural operations use the granular form for its durability and uniform spread pattern.
How to Calculate Application Rates
Because ammonium nitrate is 34 percent nitrogen (often labeled as 34-0-0), you need about 3 pounds of the fertilizer to deliver 1 pound of actual nitrogen. The math is simple: divide 100 by the nitrogen percentage. For a home lawn recommendation of 1 pound of nitrogen per 1,000 square feet, that works out to roughly 3 pounds of ammonium nitrate spread over that area.
Soil pH plays a major role in how effectively any nitrogen fertilizer works. Maintaining the correct pH for your soil type ensures that nutrients remain in forms plants can actually absorb. Over time, ammonium-based fertilizers can acidify soil, so periodic lime applications may be necessary to keep pH in the right range.
Environmental Considerations
The nitrate portion of ammonium nitrate dissolves completely in water and doesn’t bind to soil particles. That’s great for immediate plant uptake, but it also means nitrate moves wherever water moves. Heavy rain or over-irrigation can push nitrate below the root zone and into groundwater, a process called leaching. Nitrate contamination in drinking water is a health concern, and excess nitrogen reaching streams and rivers fuels algal blooms that deplete oxygen and harm aquatic life.
Long-term use of ammonium nitrate without soil management can also gradually lower soil pH. Acidified soils release fewer nutrients to plants, which can create a cycle of diminishing returns. Controlled-release fertilizer formulations and split applications (applying smaller amounts several times during the growing season rather than one large dose) help reduce both leaching losses and acidification.
Safety and Storage Risks
Ammonium nitrate is classified by the United Nations as an oxidizer, not an explosive. But that classification can be misleading. Under certain conditions, ammonium nitrate can detonate, and it has been involved in numerous industrial disasters, including the 2020 Beirut port explosion and the 2013 West, Texas fertilizer plant blast.
Fire is the most common trigger. When ammonium nitrate is heated in a confined space, it can undergo rapid decomposition that transitions from burning to detonation. Contamination makes this far more likely. Organic materials like fuel oil, sawdust, or even certain types of packing material can sensitize ammonium nitrate, as can inorganic contaminants like chlorides. This is why storage regulations are strict about keeping ammonium nitrate away from fuels, combustible materials, and incompatible chemicals.
International transport rules set detailed composition limits. Fertilizer-grade ammonium nitrate with more than 0.2 percent combustible substances, or formulations above 90 percent ammonium nitrate containing incompatible materials, are subject to tighter classification and handling requirements. Products containing 70 percent or more ammonium nitrate face additional restrictions on what other ingredients they can include.
For farmers and homeowners, the practical takeaway is straightforward: store ammonium nitrate in a cool, dry, well-ventilated area away from heat sources and any organic or combustible materials. Keep it in its original sealed packaging until use, and never mix it with fuels or oils.
Blended Forms
Pure ammonium nitrate (33 to 34 percent nitrogen) is the most concentrated solid form, but it’s not the only one on the market. Calcium ammonium nitrate, or CAN, blends ammonium nitrate with limestone to produce a product containing 20.5 to 28 percent nitrogen. The added calcium carbonate makes CAN less hygroscopic (it absorbs less moisture), safer to store, and less acidifying to soil. Ammonium sulfate nitrate, or ASN, contains about 26 percent nitrogen along with sulfur, which is a secondary nutrient many soils lack. Liquid solutions are also available for operations that apply fertilizer through irrigation systems or spray equipment.