Ammoniacal nitrogen

Ammoniacal nitrogen refers to mineral nitrogen present as the ammonium ion (NH₄⁺), as distinct from nitric nitrogen (NO₃⁻) and ureic nitrogen (urea CO(NH₂)₂). In soils, nitrifying bacteria biologically oxidise this nitrogen to nitrites (NO₂⁻), then to nitrates (NO₃⁻); nitrification inhibitors are specifically designed to slow this conversion^[1][2].

In fertilisers, ammoniacal nitrogen is found in ammonium sulphate, ammonium phosphates (DAP, MAP) and liquefied ammonia for direct application. The European regulation on fertilising products requires its content to be declared separately on the label, as a mass percentage of the nitrogen element^[3]. Urea, although containing nitrogen in amide form, undergoes enzymatic hydrolysis that releases ammonia (NH₃); urease inhibitors reduce this volatilisation by blocking the action of the urease enzyme on urea^[2].