Nitrogen in Anhydrous Ammonia

Anhydrous ammonia is 82.2% nitrogen by weight, which is not a formulation choice but simple stoichiometry: NH₃ has one nitrogen atom at 14.007 and three hydrogens at 1.008 each, so nitrogen is $14.007/17.031$ of the mass. Nothing else comes close — urea is 46%, UAN solution 28–32%, ammonium sulphate 21%.

That analysis is why anhydrous is almost always the cheapest nitrogen per kilogram delivered to the field, and it is a shipping story as much as a chemical one. Moving a tonne of nitrogen as urea means moving 2.17 tonnes of material; as ammonium sulphate, 4.76 tonnes. The nitrogen itself is identical once it is in the soil.

The offsetting cost is handling. Anhydrous is a gas at ambient pressure, stored liquefied under about 1,100 kPa, and it seeks water with such affinity that it will take it from skin and eyes instantly — the injuries are severe and specific. It requires pressurised equipment, trained applicators, and injection below the surface, and its retail availability has narrowed in several jurisdictions for security reasons.

Agronomically, the injection requirement is not merely a safety measure. Ammonia must be placed deep enough to be retained by soil moisture and clay, and applying into soil that is too dry, too wet or too coarse loses nitrogen straight back to the atmosphere. A well-sealed knife track is the difference between 82% nitrogen and a smell.