N fertilization, sowing time and cultivar selection are management practices critical to manage the dual risks of frost and heat, as well as to improve the water use efficiency of crops. The effects of the interaction between N availability and temperature on grain yield are largely unknown. The objective of this work was to study the effect of elevated temperature, sowing time, cultivar, and N rate (0 to 200 kg N ha-1) on wheat yield. Field experiments were carried out in four locations of South Australia including a combination of six modern bread wheat cultivars, four N rates, and four sowing times. An open-top passive heating system was used in a subset of two cultivars, two N rates (0, 100 kg N ha-1) and three sowing times to differentiate the effect of temperature per se. For the combined treatments, the average rate of yield decline with increasing temperature in the critical period was 0.49 t ha-1 °C-1 while the upper boundary returned a rate of 0.67 t ha-1 °C-1. The gap between the upper boundary and actual yield reached up to 4.3 t ha-1 and was higher in early- than in late-maturing cultivars. In general, applications of 50 -100 kg N ha-1 closed the gap, although rates of 100 kg N ha may increase the gap when mean temperatures during the critical period are higher than ~14.5 °C. Increasing daytime temperatures with chambers before anthesis reduced grain number and yield in unfertilized crops but not in fertilized crops. Mild warming during the critical period can seriously impair the yield of wheat, and interactions with nitrogen are likely to be important. The interaction between N supply and temperature is important in the context of climate change, crop management, and breeding.