This review examines the use of nitrogen (N) fertilizer on sugar-cane,
summer and winter grain crops, cotton, tropical fruit crops and pasto
ral areas in the four subtropical zones in eastern Australia. The path
ways for N loss from the various crops grown in these zones are also e
xamined and estimates of N loss given. Sugar-cane is the most importan
t crop grown in the subtropical humid northern and southern zones, usi
ng 77% of all N fertilizer applied in 1988-89. Urea is the most widely
used form of N fertilizer with about 50% of the applied N often lost
via ammonia volatilization, denitrification and leaching. Losses of N
via ammonia volatilization can be reduced by either irrigating after a
pplication, applying urea in subsurface bands or delaying application
until after canopy development. Denitrification losses of 20% of appli
ed N have been measured on clay soils in sugar- cane areas while leach
ing losses may occur by movement of solutes down preferential pathways
(e.g. soil fauna, root channels and structural weaknesses in the soil
profile). Tropical fruit crops also make a significant contribution t
o the economy of the humid northern and southern zones. The livestock
industry is well established in the subtropical northern zones, with b
eef and dairy production relying on leguminous as well as N fertilized
pastures. Urea is again the most widely used form of N and is suscept
ible to large losses via ammonia volatilization. Over a 12 month perio
d, losses of between 9% and 42% of the N applied were recorded from a
subtropical pasture. Wheat is the major winter crop of the sub-humid n
orthern and southern zones with grain sorghum the main summer crop. Ur
ea is the principal form of N fertilizer applied to both crops and is
essential for increasing or maintaining economic yields from both regi
ons. This decrease in soil fertility in grain producing areas is due m
ainly to a decrease in the amount of soil organic matter available for
mineralization. Cotton is another major crop of both areas and relies
heavily on N fertilizer application. Nitrogen fertilizer losses have
been recorded from all cropping areas, although nitrification inhibito
rs such as wax coated calcium carbide and 2-ethynylpyridine have reduc
ed denitrification losses from soils growing wheat and cotton respecti
vely. Subtropical agriculture relies heavily on N fertilizer, principa
lly urea, to maintain and increase crop yields. Losses of N from soils
sown to crops and from native and sown pasture occur although managem
ent practices are being developed to help minimize this loss.