Characteristics and Application of Ammonium Nitrate
Ammonium nitrate fertilizer, abbreviated as ammonium nitrate, has the molecular formula NH₄NO₃. It is currently a major nitrogen fertilizer worldwide. After World War II, ammonium nitrate production rapidly developed in the former Soviet Union and Europe and the United States. Industrial production involves converting synthetic ammonia into nitric acid under high temperature, high pressure, and platinum catalysis. The nitric acid then absorbs ammonium to form ammonium nitrate.
Ammonium nitrate fertilizer contains 33% to 35% nitrogen. Currently, there are two main types of ammonium nitrate produced: fine white crystalline granules and white or light yellow granules. Granular ammonium nitrate is highly hygroscopic and tends to form hard lumps when dried. Ammonium nitrate turns into liquid when humidity is high. If humidity changes quickly or if it’s stored without a cover, the ammonium nitrate can grow bigger and break its container. So, it needs protection from wetness when stored. If it’s in small bits and has a drying agent like mineral oil, paraffin, or apatite powder on it, it doesn’t absorb much moisture, so it can be kept in paper bags, but still, keep it away from moisture.
When applied to the soil, ammonium nitrate fertilizer quickly dissolves and ionizes into the less mobile ammonium ions and the more mobile nitrate ions. Because both are readily absorbed and utilized by crops, ammonium nitrate is a nitrogen fertilizer that leaves no residue in the soil and is considered physiologically neutral. Due to the high mobility of nitrate, ammonium nitrate is generally not used as a base fertilizer or as a topdressing during the rainy season, except in special circumstances. Ammonium nitrate is more effective as a topdressing fertilizer for dry land. Ammonium nitrate is suitable for all types of soil and crops, but is not suitable for paddy fields. Ammonium nitrate is not suitable for seed fertilizer because it absorbs moisture and dissolves, causing severe salt damage, which can affect seed germination and seedling growth.
For storage, transportation, and application safety considerations, as well as the potential for nitrate nitrogen hydrolysis and food contamination, some countries have clear regulations regulating the application and quantity of nitrate nitrogen fertilizers. Modification of ammonium nitrate is an important way to improve its hygroscopicity and prevent flammability and explosion hazards. The most important ammonium nitrate-modified nitrogen fertilizers are calcium ammonium nitrate and ammonium sulfate nitrate.
Calcium ammonium nitrate, also known as lime ammonium nitrate, is primarily composed of NH₄NO₃ and CaCO₃, with a nitrogen content of approximately 20%. It is processed by eutectic melting of ammonium nitrate and calcium carbonate. Ammonium sulfate nitrate is produced by eutectic melting of ammonium nitrate (approximately 74%) and ammonium sulfate (approximately 26%); or by mixing nitric acid and sulfuric acid, absorbing ammonia, crystallizing, and drying into granules.
Sodium Nitrate
Sodium nitrate(Chilean saltpeter), is famous for its abundant production in Chile. Besides natural mineral deposits, sodium nitrate can also be processed and produced using nitric acid. The molecular formula of its active ingredient is NaNO₃.
Peru saltpeter contains 15% to 16% nitrogen. It shows up as white or light crystals and mixes well with water. At 10℃, you can dissolve 96 grams of it in 100 grams of water. It starts absorbing moisture when the relative humidity hits 74.7% at 20℃. Also, it’s more stable compared to ammonium nitrate. Farmers have used sodium nitrate for a while to fertilize dryland crops like tobacco and cotton, and it works pretty well. For crops that prefer sodium, like beets and spinach, calcium nitrate fertilizers often produce better results than other nitrogen fertilizers.
Calcium Nitrate
Calcium nitrate is often produced by the reaction of calcium carbonate with nitric acid and is a byproduct of certain industrial processes.
Pure calcium nitrate is seen as fine, white crystals. When used as fertilizer, it shows up as gray or pale yellow granules. It has about 13% to 15% nitrogen. This fertilizer absorbs water easily, starting at 54.8% relative humidity when the temperature is 20°C. It dissolves in air on its own, so keep it sealed when storing and moving it. Calcium nitrate is readily soluble in water, and its aqueous solution is acidic. Calcium nitrate exhibits a weak alkalinity during crop absorption, but because it contains sufficient calcium ions, it does not cause side effects, making it suitable for a wide range of soils and crops. Calcium nitrate containing 19% water-soluble calcium is particularly suitable for crops such as vegetables, fruit trees, peanuts, and tobacco.
