Anhydrous ammonia

Anhydrous ammonia is nitrogen and hydrogen with no added water, at about 82% nitrogen. It is produced industrially from atmospheric nitrogen and hydrogen and is the primary feedstock for urea, ammonium nitrate, ammonium sulfate, and other nitrogen fertilizers.

Chemical formula

NH₃

Nitrogen content

About 82% nitrogen, the highest of common fertilizers

Physical state

Liquefied gas under pressure; a gas at ambient conditions

Reaction in soil

Combines with soil water to form ammonium near the injection band

Anhydrous ammonia supplies nitrogen only. On injection it converts to ammonium, which is initially held near the band and then nitrifies to nitrate over time. The concentrated band of ammonia can temporarily raise pH and be toxic to microbes and seedlings in its immediate zone until it disperses.

• Forms ammonium on contact with soil moisture, retained near the injection band
• Ammonium subsequently nitrifies to nitrate through soil microbial activity
• Supplies no phosphorus, potassium, or sulfur

Anhydrous ammonia is injected below the soil surface through knife or shank applicators into moist soil that can seal behind the injection slot to retain the gas. Adequate injection depth, soil moisture, and slot closure are central to limiting loss of ammonia to the air at application.

• Requires injection below the surface into soil with adequate moisture and sealing
• Very low cost per unit of nitrogen where handling infrastructure exists
• Seed or seedling contact with the concentrated band must be avoided

Anhydrous ammonia is strongly attracted to water and will react with the moisture in eyes, skin, and the respiratory tract, causing severe caustic burns and, on rapid release, freezing injury. Handling, storage, and transport are governed by strict safety and regulatory requirements in most jurisdictions.