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 uncertai n because yield responses depend on a good supply of soil moisture during t he growing of the crop to provide a high potential yield. While an experime nt in 1996 indicated that up to 90 kg N/ha of N fertiliser is profitable, i t 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 produ ce 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 conditio ns in that year. Under typical growing conditions, it is not economic to us e N fertiliser. The simulations quantified the relationship between respons es to fertiliser and the amount of soil moisture available at sowing. Appli cations of N fertilisers will be most profitable if used when measurements indicate that the plant-available soil moisture content before sowing is ab ove average. (C) 1999 Elsevier Science Ltd.