There is concern about environmental impacts of cropping in catchments of Australia’s Great Barrier Reef,
especially losses of nitrogen (N) from cropping systems. Sugarcane production in the Burdekin region in
the dry tropics stands out from other crops/regions because it is grown with the highest applications of
irrigation water and N fertiliser rates of any sugarcane producing region in Australia, attributes which may
enhance losses of N. Little is known about N losses fromsugarcane production systems, especially irrigated
systems. We measured parts of the water and N balance over three sugarcane crops at three contrasting
sites in different parts of the Burdekin region, covering a range of soil types/textures and irrigation
managements. The experimental data were used to parameterise the APSIM-Sugarcane cropping systems
model, and the model then used to ‘infill’ missing data and develop more complete water and N balances
for each of the crops at the three sites. The model was also used to simulate long-term yields and N losses
through runoff and leaching below the root zone at the sites under a range of N fertiliser and irrigation
management practices. Unlike the experience in other cropping systems, N losses through runoff and
leaching below the root zone were not higher at our sites than measured in rainfed sugarcane production
systems. The long-term simulations showed there were clear opportunities for reducing N losses while
maintaining yields through reducing N fertiliser application rates. Simulations results suggested that
long-term N surpluses of 50 kg ha
−1
yr
−1
, considerably less than those during the experiment or common
in the study region, were sufficient to maintain yields but reduce N losses by 50–57%. So, N fertiliser
management should aim to keep surpluses to that level. Improved irrigation management could also help
reduce N losses but generally to a much lesser extent than reduced N fertiliser applications. Research is
required to confirm these predicted benefits, and investigate potential interaction between N fertiliser
and irrigation management practices, and impacts of other management practices.