The ammonium ion is less likely to be leached from soil than the nitrate ion, so inorganic fertilisers are mostly ammonium salts.
From the newscientist.com
Ammonia gas passed into a strong aqueous solution of the polycarbonate displaces the hydrogen ion with an ammonium ion, converting it into ammonium carbonate.
From the en.wikipedia.org
For example, replacing formic acid by volatile basic additives such as ammonium hydroxide facilitates the detection of metabolites in the negative ion mode.