Using the APSIM model to estimate nitrous oxide emissions from diverse Australian sugarcane production systems

Sugarcane is an important crop in the tropics and sub-tropics and its production requires very high rates of nitrogen (N) fertiliser. This N use, together with the warm, wet environment in which it grows, produces a high potential for emissions of the greenhouse gas nitrous oxide (N2O) from soils. The few measurements of N2O emitted from sugarcane are higher than expected from the level of N applied or experience in other crops. Accordingly, we simulated long-term N2O emissions over a range of environments and sugarcane management practices. Simulations were undertaken with the cropping systems model, APSIM, after we (1) tested the denitrification sub-model and (2) added a mechanistic N2O prediction capability to the model. Predicted N2O emissions agreed well with data from two field experiments measured, provided the default value of the model's denitrification rate coefficient was substantially increased. We predict N2O emissions from soils in Australian sugarcane production may commonly be equivalent to 3–5% of N fertiliser applications across a wide range of environments, including some where field studies have yet to be undertaken. As expected, predicted emissions varied between regions and soils, being higher in clay soil, where substantial irrigation was applied and where crop residues were retained. Reducing N fertiliser applications would obviously help reduce N2O emissions. It has been previously suggested that there is potential for substantial reductions (e.g. by 30%) in Australian sugarcane production so this is one pathway to help reduce N2O emissions. However, it is also important to better understand the interactions between specific site (soil and climate) and management (N fertiliser, crop residue and irrigation) factors influencing N2O emissions to find other opportunities to reduce emissions.