Modelling wheat production from low-rainfall farming systems in Northern Australia

Wheat yields are highly variable in northern Australia because rainfall is variable. Economic benefits from applying nitrogen fertilisers are uncertain because yield responses depend on a good supply of soil moisture during the growing of the crop to provide a high potential yield. While an experiment in 1996 indicated that up to 90 kg N/ha of N fertiliser is profitable, it was not known whether this response is reliable or typical. A crop model and historical climate records (1960–1993) were used in this study to produce a long-term record of yield and grain protein responses to N fertilisers. Responses in 1996 are shown to be atypical due to the favourable conditions in that year. Under typical growing conditions, it is not economic to use N fertiliser. The simulations quantified the relationship between responses to fertiliser and the amount of soil moisture available at sowing. Applications of N fertilisers will be most profitable if used when measurements indicate that the plant-available soil moisture content before sowing is above average.