Timing of nitrogen in low rainfall canola, Salmon Gums 2014 trial report

Page last updated: Monday, 14 October 2019 - 5:08pm

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In general, as long as nitrogen is applied within eight weeks of sowing, there is no yield penalty.

How canola responds to nitrogen applied later than eight weeks has not been widely researched. Similarly how new generation canola such as RoundupReady (RR) hybrids respond to nitrogen has not been widely tested, particularly in low and medium rainfall areas


With grain yield of less than 1t/ha, there was only a small grain yield response to applied N and no economic response to applied N. Top-up N at 12 weeks gave a similar response to top-up N at eight weeks.


To investigate the response to changing the nitrogen rate and changing the time of application. Canola yield and oil will be measured and RR hybrids will be compared with open-pollinated TT types (OP TT).

Trial details

Table 1 Trial details
Property Tim, Dave and Fiona Osborne’s, Eldred Road, Salmon Gums
Agzone 5 growing season rainfall (GSR, April to October) 175mm, GSR + stored water (estimate) = 198mm
Soil type Sandy loam (0.7% organic carbon), estimated to be 58kg N/ha available in paddock from soil and plant residues
Paddock rotation 2013 - barley. 2012 - wheat, 2011 - wheat, 2010 - field pea
22 treatments Two cultivars (Sturt TT [TT open-pollinated variety] and Pioneer 43Y23RR [RR hybrid variety]) x 11 N treatments (kg N/ha) with timing spread between seeding, and up to 12 weeks after sowing (see Table 2)
Replicates Three
Sowing date 17 April
Seeding rate Target density 30 plants/m2 - Sturt TT 2.4kg/ha, Pioneer 43Y23RR 1.5kg/ha
Basal fertiliser 400kg/ha of gypsum (17% Ca, 14% S) top-dressed over whole site before sowing (kg/ha),100kg/ha of Impact treated Superphos at seeding, 120kg/ha of Muriate of Potash top-dressed over whole site four weeks after seeding
Table 2 Treatment details, Salmon Gums 2014
Treatment Name Seeding 8WAS 12WAS Total N
1 Nil 0 0 0 0
2 10N seeding 10 0 10 0
3 30N in eight weeks 10 20 0 30
4 50N in eight weeks 10 40 0 50
5 70N in eight weeks 10 60 0 70
6 10N seeding and 20N 12WAS 10 0 20 30
7 10N seeding and 40N 12WAS 10 0 40 50
8 10N seeding and 60N 12WAS 10 0 60 70
9 30N in eight weeks and 10N 12WAS 10 20 10 40
10 30N in eight weeks and 20N 12WAS 10 20 20 50
11 30N in eight weeks and 40N 12WAS 10 20 40 70

Assumptions used in gross margins

Oil bonus: +/- 1.5% per unit of oil (%) either side of 42%, with no oil ceiling.

Additional costs such as seeding, harvest, insecticides assumed to be $126/ha.

Nitrogen costs: $1.33/kg or $1.5/L, application costs $8/ha

RR costs: seed $76/ha, Herbicides $47/ha, Grain worth $513t (5 Year decile price)

TT costs: seed $5/ha, Herbicides $56/ha, Grain worth $535/t


No difference between varieties therefore we are presenting the mean results only.

Grain yield of canola started to plateau at 30 kg N/ha
Figure 1 Effect of nitrogen fertiliser on the grain yield (kg/ha) of canola at Salmon Gums in 2014 (14ED15), LSD = 71kg/ha
Oil concentration in the seed of canola decreased as nitrogen rate increased
Figure 2 Effect of nitrogen fertiliser and split applications on the oil content (%) of canola at Salmon Gums in 2014 (14ED15), LSD = 0.6%
Gross margins of canola were maximised at an applied nitrogen rate of 10 kg/ha
Figure 3 Effect of nitrogen fertiliser and split applications on the oil content (%) of canola at Salmon Gums in 2014 (14ED15), LSD = 0.6%


In a relatively dry growing season at Salmon Gums grain yield responded to around 30kg N/ha. The gain in yield was relatively small at around 5kg per unit of N applied and oil decreased with each kg of N. Therefore it was uneconomic to apply N to canola. When N was applied had no effect on the yield or oil response. This experiment is an example where by delaying N top-up until later in the year may have allowed growers to decide not to apply N.


This trial (14ED15) is one of a series conducted throughout WA as part of the GRDC/DPIRD co-funded project Tactical Break Crop Agronomy in Western Australia. Thanks to the Osborne family for hosting the trial and to the Esperance RSU for trial management. Pam Burgess (DPIRD Esperance) provided technical assistance to ensure all treatments and measurements occurred in a timely and accurate fashion.

Contact information

Mark Seymour
+61 (0)8 9083 1143