Ammonium nitrate

Ammonium nitrate is produced by reacting ammonia with nitric acid, then granulated or prilled for field use. Its nitrogen content, typically around 34%, is split roughly evenly between the ammonium (NH₄⁺) and nitrate (NO₃⁻) ions.

Ammonium nitrate supplies nitrogen only, in two forms simultaneously. The nitrate fraction is immediately available for root uptake, while the ammonium fraction is retained more strongly by soil and nitrifies over subsequent days to weeks, depending on temperature and moisture.

• Nitrate portion is plant-available immediately and mobile in the soil solution
• Ammonium portion is held on soil cation exchange sites and nitrifies over time
• Supplies no phosphorus, potassium, or secondary or micronutrients

Ammonium nitrate is widely used on cereals, forage grasses, and other crops in temperate regions, particularly where its combination of immediate and slightly delayed nitrogen release, and comparatively lower ammonia-volatilisation risk than urea, are valued.

• Dual ammonium and nitrate supply offers both quick and short-delay availability
• Lower ammonia-volatilisation risk than urea when surface-applied
• Commonly used in split top-dressing programs on cereals and grassland

General practice is to time applications to crop demand and to split doses across the season where appropriate, since the nitrate component is mobile and subject to leaching in wet conditions. Storage and transport of ammonium nitrate are governed by safety regulations in most countries because of its oxidising properties.

The nitrate fraction of ammonium nitrate is highly mobile and can leach below the root zone in wet conditions or on coarse-textured soils, posing a risk to groundwater and surface water. Denitrification of nitrate under saturated soils can also release nitrous oxide, a potent greenhouse gas.