How much fertiliser does canola need? Nitrogen requirements for canola

How much nitrogen canola needs

A review in Crop and Pasture Science (CSIRO Publishing) found that, across Australian measurements, each tonne of canola seed needed about 80 kg of nitrogen taken up by the crop. That figure underpins most canola nitrogen budgets.

Incitec Pivot gives the same rule of thumb with a comparison: about 40 kg N per tonne of grain for wheat and 80 kg N per tonne for canola.

Nitrogen also lifts protein and lowers oil. NSW DPI trials found oil content fell as nitrogen rates rose, but the review notes that oil yield and the overall value of the crop usually still increase.

Budget it: demand minus supply

The review describes the usual approach: supply 80 kg N per tonne of target yield, less what the soil supplies. Incitec Pivot lists the credits as soil mineral nitrogen, mineralisation (N released from organic matter) and fertiliser.

1. Set a realistic yield target from stored soil water and expected rain (water-limited yield), and update it as rain records come in.
2. Multiply by 80 to get total N supply needed. Example only: 2 t/ha × 80 = 160 kg N/ha.
3. Subtract soil supply from a deep soil N test and your agronomist's estimate of in-season release. If that comes to 90 kg N/ha, the gap is 70 kg N/ha.
4. Convert to product. Urea is 46% N, so 70 ÷ 0.46 ≈ 152 kg/ha of urea.

Those numbers are for illustration. Your soil test, paddock history and season set the real figures. The wheat nitrogen budget worked example walks through the same method step by step, and cost per kg of nitrogen helps you compare products such as granular urea, Summit Urea or liquid EASY N. Browse all nitrogen fertilisers.

In central-western NSW, NSW DPI trials at Nyngan and Trangie found canola responded to nitrogen even with moderate to high soil N, and suggested growers apply at least 30 kg N/ha there.

Timing and splitting

• Canola takes up nitrogen fastest during stem elongation, then through branching, flowering and podding. Before stem elongation, less than 10% of the season's nitrogen has been taken up.
• Rate matters more than timing. NSW DPI found no difference between nitrogen at sowing or in crop at Nyngan and Trangie.
• The review says the budget can be split over two, three or more applications with little loss of efficiency. That lets you wait and see the season before committing the rest.
• Topdressed urea can lose N to the air. See urea volatilisation, urea vs UAN, or compare granular urea and EASY N side by side.

Phosphorus at sowing and seed safety

Incitec Pivot calls canola the most susceptible crop to fertiliser toxicity. Damage comes from ammonia released near the seed and from fertiliser salts drawing water away from it (osmotic effect). Dry soil at sowing makes it worse.

• Nitrogen with the seed: in a NSW DPI trial at Merriwagga on red sandy loam, urea at 30 kg N/ha or more placed with the seed cut yield through poorer establishment. The authors concluded canola is very sensitive to more than 15 kg N/ha with the seed. Put the rest of the N in a separate pass or band it away from the seed.
• Phosphorus source: MAP is the safer choice in the seed row; DAP releases more ammonia. See MAP vs DAP and compare MAP, Impact MAP or Summit MAP 11-52.
• Placement: Incitec Pivot suggests at least 50 mm between seed and fertiliser, below and to the side. Sandy soils and wider rows raise the risk.
• Split P: where a lot of P is needed, a small starter rate of about 5 kg P/ha with the seed plus a broadcast pre-sowing application can cut toxicity risk while holding yield, according to Incitec Pivot trials in NSW.
• Canola grain removes more P per tonne than wheat (3.6–7.2 vs 2.3–3.6 kg P/t), so set rates from a soil test. See reading a soil test.

Canola also needs more sulphur than cereals; see sulphur deficiency in canola. Always check with your agronomist before acting.