Plant density in low rainfall canola, Salmon Gums 2014 trial report

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Canola is now being grown in low rainfall areas. Primarily farmers choose open pollinated TT varieties. Hybrids provide growers with more vigorous seedlings, comparatively better plant establishment and generally higher yields. However growers have to purchase new seed of hybrid varieties every year in order to get these potential yield benefits. Seed for hybrid canola is 25 times more expensive than the seed of open pollinated canola. Inevitably if farmers are forced into hybrids they will wish to minimise seed costs by sowing at low densities.


  • RR hybrid canola maximised gross margins
  • OP TT variety Sturt produced similar gross margins to the hybrid TT variety Hyola 450 TT
  • Gross margins were optimised at:
    • ~50 plants/m2 for Sturt TT
    • ~5-25 plants/m2 for Hyola 450TT
    • ~13 plants/m2 for Pioneer 43Y23 RR


To investigate the plant density response to yield and oil content of TT and RR hybrid canola in comparison with open-pollinated canola.

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
Sowing date 6 May
Fertiliser 400kg/ha of gypsum (17% Ca, 14% S) top-dressed over whole site before sowing (kg/ha),107kg/ha of Impact treated Agras No.1 at seeding, 100L UAN/ha on 19 June, 1L Mantrac/ha on 9 July and 120kg/ha of muriate of potash top-dressed over whole site 10 July
28 treatments

Four varieties x eight target densities

Two HT - Herbicide tolerant canola (TT and RR)

TT– OP = Sturt TT and Hybrid = Hyola 450TT

RR -  OP = GT Viper (data not shown due to low field establishment), Hybrid = Pioneer 43Y23 RR

Eight target densities of 5, 10, 15, 20, 30, 40, 60, or 80plants/m2. Seed rates were adjusted for germination, seed size and estimated field establishment- which varied with target density and seed type

Replicates Three

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 $100/ha.

Nitrogen costs: $1/kg, application costs $8/ha.

RR costs: OP seed $25/kg, hybrid seed $33/kg, herbicides $28/ha, grain worth $513/t (Decile 5 price).

TT costs: OP seed $3/kg, hybrid seed $24/ha, herbicides $46/ha, grain worth $535.


The OP TT variety Sturt responded to plant densities above 50 plants/m2, Hyola 450TT seed yield responded up to 25 plants/m2 while gross margins were similar at 5-25 plants/m2. Pioneer 43Y23 RR had approximately 20% higher establishment than we anticipated and its yield and gross margin plateaued at approximately 13 plants/m2.

RR hybrid canola maximised gross margins, whilst there was no difference between OP or hybrid TT canola.

Table 2 Target and actual plant density, seed yield (GY, kg/ha) and gross margin (GM, $/ha) of three canola varieties at Salmon Gums in 2014
Variety and target density Established plants per m2 GY GM
Sturt TT 5 3 446 -70
Sturt TT 10 7 552 -14
Sturt TT 15 744 89
Sturt TT 20 14 765 103
Sturt TT 30 19 794 115
Sturt TT 40 38 802 114
Sturt TT 60 46 818 126
Sturt TT 80 64 911 165
Hyola 450 TT 5 5 772 114
Hyola 450 TT 10 9 780 111
Hyola 450 TT 15 16 813 120
Hyola 450 TT 20 25 895 158
Hyola 450 TT 30 30 797 87
Hyola 450 TT 40 49 972 141
Hyola 450 TT 60 72 819 14
Hyola 450 TT 80 84 864 -8 
Pioneer 43Y23 RR 5 7 735 121
Pioneer 43Y23 RR 10 13 898 200
Pioneer 43Y23 RR 15 16 949 218
Pioneer 43Y23 RR 20 26 981 222
Pioneer 43Y23 RR 30 36 958 194
Pioneer 43Y23 RR 40 67 976 137
Pioneer 43Y23 RR 60 93 931 48
Pioneer 43Y23 RR 80 123 1003 21
- P P P
Cultivar <.001 <.001 <.001
Density <.001 <.001 <.001
Cultivar density <.001 <.001 <.001


The results from this trial confirmed the results from previous years, with OP TT canola responding to higher plant densities than other canola due to a combination of the biological response and the low cost of increasing OP TT density. Similarly RR hybrid canola showed a flat response to plant density and consequently a relatively low plant density maximised returns. Hybrid canola responded somewhere in-between, with yields responding to higher densities than RR hybrid canola. Hybrid TT did not produce higher gross margins than OP TT, therefore the low risk option in low rainfall areas remains OP TT, with RR hybrids being the best option if weeds develop resistance to triazine herbicides.


This trial (14ED10) 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
+61 (0)8 9081 3126