gas is obtained from the air, which is about 79% nitrogen by volume, and the hydrogen is
obtained from natural gas (methane), oil, coal, water, or other sources.
and Moldovan et al. (154)
describe the production of other nitrogen fertilizers from
ammonia. A brief summary of these processes follows. Nitric acid, produced from ammonia, is
another basic material in the manufacture of nitrogen fertilizers. To produce nitric acid, compressed
ammonia and air are heated in the presence of a catalyst and steam. The nitric acid can be reacted
with ammonia to produce ammonium nitrate. Sodium nitrate is the product of the reaction of nitric
acid with sodium bicarbonate. Sodium nitrate also is produced from caliche (Chilean saltpeter),
which is a mineral that contains sodium nitrate and various salts of sodium, calcium, potassium, and
magnesium. Sodium nitrate, sometimes called Chilean nitrate, is one of the earliest commercial
nitrogen fertilizers marketed. Until 1929, all of the sodium nitrate marketed was extracted from
Chilean saltpeter (154)
. Urea is manufactured chiefly by combining ammonia with carbon dioxide
under high pressure. Ammonium sulfate is manufactured by the reaction of ammonia with sulfuric
acid, gypsum, or sulfur dioxide.
The merits of nitrate and ammonium fertilizers have been researched and reviewed extensively
. Many manufactured fertilizers and most organic fertilizers are ammonical; however, the
ammonium that is inherent in the fertilizer or that is released upon contact with soils is soon oxidized
to nitrate, unless nitrification is inhibited (167–171)
. Nitrification inhibitors may be employed with
ammoniacal fertilizers to restrict losses of nitrogen from soils by leaching or denitrification.