To examine the nitrogen use efficiency of canola grown under overhead irrigation when increasing rates of nitrogen fertiliser applied (Prilled Urea 46%N)

• Seed yield (3.90 t/ha) was maximised when 240kg N/ha was applied as a two split application and although yield increased up to 320kg N/ha the advantage in seed yield was not statistically significant.
• There was no significant effect on seed oil content (45.9 – 48.3%) across the different rates of nitrogen fertiliser applied.
• When no nitrogen was applied the test weight was significantly lower (62.4 kg/hl) than all the other nitrogen applications (63.3 – 64.1 kg/hl).
• There was no significant difference in harvest index (HI) although values varied from 23 -31% with the N rates applied.
• Seed yield showed little relationship with dry matter content of the crop at 80% flowering.
• No removed in the crop canopy at flowering revealed a soil N supply of approximately 70kgN/ha in the absence of fertiliser applied.
• At 200kg N/ha applied fertiliser and below more N was removed in dry matter at flowering with N doses of 200kg N/ha and below.
• When applied fertiliser was 240kg /ha N or greater less N was removed in dry matter at flowering than was applied.