Chemistry Reference
In-Depth Information
(NH
4
NO
3
), ammonium phosphate ((NH
4
)
3
PO
4
)
and potassium chloride (KCl) in varying proportions
(Figure 11.19). Fertilisers have an important role in
the nitrogen cycle (see below).
Figure 11.20
Fertilisers have been used to help create some of the best
fruit on sale.
a
Different fertilisers contain differing amounts of the elements nitrogen,
phosphorus and potassium.
Manufacture of ammonium nitrate
Ammonium nitrate (Nitram®) is probably the most
widely used nitrogenous fertiliser. It is manufactured
by reacting ammonia gas and nitric acid.
ammonia + nitric acid → ammonium nitrate
NH
3
(
g
) + HNO
3
(
aq
) →
green
foliage
strong
roots
NH
4
NO
3
(
aq
)
The nitrogen cycle
The vital importance of nitrogen to both plants and
animals can be summarised by the
nitrogen cycle
(Figure 11.21).
healthy
growth
b
The different NPK elements are responsible for the healthy growth of
plants in different ways.
Figure 11.19
nitrogen in the air
nitrogen fixation*
animals eat plants
fertilisers produced
by the Haber process
plants use nitrates
to make proteins
remains of
dead plants
and animals
nitrogen-fixing bacteria
in soil and root nodules
of some plants
excreted
waste
nitrates in the soil
Figure 11.21
The nitrogen cycle.
*Nitrogen fixation
is the direct use of atmospheric nitrogen in the formation of important compounds of nitrogen. Bacteria present in the root
nodules of certain plants are able to take nitrogen directly from the atmosphere to form essential protein molecules.
