Making the most of irrigated canola

May is the best time to sow irrigated canola in Victoria.

A project funded by growers through the GRDC investigated the effects of water, nitrogen fertiliser and time of sowing on yield and oil content of canola grown on irrigated red-brown soils in Victoria.

Yield of seed and oil fell as the sowing date was delayed after May. April- and May-sown crops yielded about the same, although the former produced more dry matter and frequently lodged.

Seeding rate

Seed and seedling losses and the uniformity of establishment are especially influenced by seed-bed conditions. A population of about 50 plants/m2 was required.

Nitrogen increases yields

Canola has a high nitrogen requirement and needs up to 100 kg/ha, depending on the fertility level of the paddocks. Nitrogen fertiliser increased seed and oil yields, and these were even better with irrigation. However, without adequate soil moisture large quantities of nitrogen fertiliser applied at sowing and rosette stage will be completely wasted.

Split applications gave no advantage. The recovery of nitrogen fertiliser varied from 45 to 65 per cent, which indicates that between 35 and 55 per cent of the fertiliser was not in the crop at maturity despite the depletion of soil mineral nitrogen. Denitrification probably accounts for the 'missing' nitrogen.

Further research is needed to match nitrogen supply to demand from the crop.

Crop rotation

Canola has a useful role in crop rotation, and is one of the few winter crops which can be irrigated. It requires irrigating as frequently as a wheat crop. When using canola in crop rotation, growers should not sow it again in the same paddock for about three years, and preferably not next to canola stubble. Blackleg, a fungal disease which attacks canola causing severe yield losses, is carried over on the stubble.

Sowing techniques will also be researched in future, since the need for a fine seed-bed might deter growers who favour minimum tillage. Suitable direct drilling techniques would make canola more attractive.


Late March

  • Pre-irrigate


  • Prepare a fine seedbed


  • Apply and incorporate trifluralin herbicide
  • Apply and incorporate 100 kg/ha of nitrogen
  • Sow a recommended variety at 7-10 kgs/ha with 250 kg/ha of single superphosphate
  • Sow by dropping seed onto the soil surface, and covering

June & July

Control Red-Legged Mite:

  • Apply post sowing herbicides as required — several herbicides are available for grasses whereas Lontrel (R) is the only chemical registered for use on broadleaf weeds.


  • Irrigate approximately every 2 weeks


  • Windrow the crop early to mid-November when approximately one-third of the seeds have changed from green to brown
  • Harvest the dry crop about 10 days later

Region North, South, West