Can agronomy overcome yield penalty of retained (F2) hybrid TT canola in the low rainfall zone? Merredin 2015 trial report

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In the trial series at Grass Patch, Ballidu, Merredin and Holt Rock, the highest grain yields, oil and gross margins were from the open pollinated variety, so growers should continue to use open pollinated TT varieties in the low rainfall regions, rather than hybrids.

In the hybrid treatments, there were generally increased yields and oil from the purchased (F1) seed, compared with the retained (F2) seed.

Agronomy reduced the yield penalty from growing retained (F2) seed. Where growers choose to use hybrid varieties, grade to increase seed size and target high plant density.


Nearly 80% of area sown to canola in WA is still open pollinated (OP) triazine tolerant (TT) varieties. However, breeding companies are favouring the development of hybrids in order to pay for breeding services. 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, which is 25 times more expensive than the seed of open pollinated canola.

This trial is investigating if farmers in the low rainfall region are better off using purchased (F1) or retained (F2) TT hybrid canola seed.

This trial is part of a series, where the same trial is repeated at Grass Patch, Ballidu, Merredin and Holt Rock.


To investigate whether agronomy can overcome the yield penalty of retained (F2) TT hybrid canola compared with purchased (F1) hybrid seed by using;

  • seed mixes
  • increased density or
  • grading to increase seed size

Trial details

  • DPIRD Merredin Research Station
  • Agzone 4, Growing season rainfall (GSR) = 191mm
  • Sowing date: 23 April 2015
  • Fertiliser: Sulfate of ammonia 19g/ha on 11 May, further 13g/ha on 22 May and 800mL/ha on 11 August.
  • There were machinery problems at harvest, and a 10 day break between the start and end of harvest for this trial

Treatment details

Nine treatments:

  • Purchased (F1) and retained (F2) Hyola 450 TT, OP comparison, ATR Bonito

Agronomy treatments;

  • Seed size; retained seed (F2) graded over and below 1.8mm sieve
  • Mixes; 25, 50 and 75% purchased (F1), with remainder being retained (F2) seed
  • Density; two densities of 20 or 40 plants/m2

Two different commercial seed lots of Hyola 450 TT F1 seed were used, purchased in 2014 and 2015. 2015 seed of ATR Bonito was used as an open-pollinated control. All trials were sown using DPIRD cone seeders at a depth of 2cm, followed by press wheels. Trial plots were 20m x 1.54m. A randomised complete block design with three replicates was used.

All trials were sown at two target densities. The graded F2 seed was retained on a 1.8mm screen, while the small seed passed through that screen. Different F1:F2 seed mixes were prepared, using the 2015 F1 seed. Seeding rates were calculated according to the target density, expected field establishment, seed size and germination per cent (Table 1). Establishment counts were taken 4-6 weeks after sowing by counting 10m of plants, over five locations within each plot. Plots were machine harvested and oil and protein measured on samples from each plot.

Table 1a Treatments and seed information
Seed Seed size (mg) Seeds/kg Germination (%) Expected field establishment
Hyola 450 TT F1 2014 5.53 180 766 88 85
Hyola 450 TT F1 2015 4.26 235 000 97 85
Hyola 450 TT F2 3.30 302 755 99 85
Large Hyola 450 TT F2 3.91 255 754 100 85
Small Hyola 450 TT F2 3.12 320 513 100 85
Mix 25% F1#: 75% F2 mix mix mix 85
Mix 50% F1#: 50% F2 mix mix mix 85
Mix 75% F1#: 25% F2 mix mix mix 85
ATR Bonito (OP) 4.35 320 000 98 75
Table 1b Seeding rates and seed costs
Seed Seeding rate (kg/ha) @ 20 plants/m2 Seeding rate (kg/ha) @ 40 plants/m2 Seed cost ($/ha) @ 20 plants/m2 Seed cost ($/ha) @ 40 plants/m2
Hyola 450 TT F1 2014 1.5 3.0 35.50 71.00
Hyola 450 TT F1 2015 1.0 2.1 24.77 49.55
Hyola 450 TT F2 0.8 1.6 1.57 3.14
Large Hyola 450 TT F2 0.9 1.8 1.84 3.68
Small Hyola 450 TT F2 0.7 1.5 1.47 2.94
Mix 25% F1#: 75% F2 0.8 1.7 7.37 14.74
Mix 50% F1#: 50% F2 0.9 1.8 13.17 26.34
Mix 75% F1#: 25% F2 1.0 1.9 18.97 37.94
ATR Bonito (OP) 1.2 2.4 2.37 4.73

# 2015 F1 used in seed mixes.

Note that the difference in seeding rates between the two purchased seed treatments is due to differences in seed size and germination per cent.

Assumptions used in gross margins

  • Oil bonus +/- 1.5% per unit of oil (%) either side of 42%, with no oil ceiling.
  • Seed costs at $2/kg for ATR Bonito and retained hybrid (F2) seed Hyola 450 TT, range $1.50 to $4.70. Seed costs at $24/kg for purchased (F1) hybrid seed Hyola 450 TT, range $24.77 to $71.00 at high density).
  • $5 end point royalty for OP variety, ATR Bonito.
  • $260 used for other costs except seed, for both canola varieties. This included  $58 for herbicides, $78 for fertiliser, also insecticides, fungicide, insurance, labour, repairs, depreciation, fuel and interest.
  • Long term canola price used of $555, which was $513 at farm gate, after cartage and CBH costs.


Merredin trial results

The overall field establishment was 65%. This was a high of 88% for the 2014 F1 and 60% for the 2015 F2. While the F2 was 63%. The grading caused differences with an increase to 68% for the large F2 seed although also an unexplained increase to 67% for the small F2 seed. There was no difference in field establishment with different densities.

Although there was a solid establishment of 65% overall, the calculated seeding rate was too low so the actual plant density was 15 and 31 plants/m2, rather than the target densities of 20 and 40 plants/m2.

Table 2 Gross margin, grain yield and oil results
  GM ($/ha) GM ($/ha) GY (kg/ha) GY (kg/ha) Oil (%) Oil (%)
Target density (plants/m2) 20 40 20 40 20 40
OP 143 290 734 990 47.8 48.9
F1 2014 259 272 1010 1094 47.3 47.8
F1 2015 216 191 911 917 47.5 47.0
F2 small 194 154 851 776 45.8 45.8
F2 ungraded 122 137 704 740 46.7 46.4
F2 large 122 110 712 693 46.2 46.1
25% F1: 75% F2# 89 248 656 969 46.7 46.1
50% F1: 50% F2# 69 412 630 1273 46.6 47.2
75% F1: 25% F2# 191 252 854 1010 47.6 46.8
LSD 126.3 126.3 230.3 230.3 0.79 0.79

# 2015 F1 used in seed mixes.

For simplicity in reporting, only the results of the 2015 purchased seed (F1) are discussed, not the 2014 F1.

Overall, there was a 21% (190kg) yield loss from using 2015 retained (F2) seed, rather than purchased (F1) hybrid TT canola, a drop in oil of 0.6% and $71 (35%) drop in gross margin (from average of 20 and 40 plants/m2 densities).

Mixes of seed produced a relatively linear response; the more purchased (F1) seed in the mix, the better was the yield, oil and gross margin.

Increasing the density of the retained (F2) seed only produced a small yield increase of 35kg/ha, which was very similar to the yield of the purchased (F1) seed. There were greater yield gains from increasing the density, in the associated trials at Grass Patch and Ballidu.

Grading the F2 seed to increase the seed size, did not have any yield, oil or gross margin benefits in this trial.

Growers generally use a higher plant density for (cheap) retained seed, compared with purchased seed. In this trial, grading the retained seed to a larger size and sowing at a higher density did not improve the performance or gross margin of the retained seed, compared with the purchased seed grown at the lower plant density.

The best gross margin from the trial were the open pollinated variety ATR Bonito, at 990kg/ha yield, 48.9% oil and a gross margin of $290/ha, (apart from an anomalous gross margin of $412 from the 50% F1 mix).

graph of results as described in the text and in table 2
Figure 1 Grain yield, oil and gross margin comparison of retained (F2) hybrid graded and sown at high density, with 2015 purchased (F1) hybrid at lower density and open pollinated variety ATR Bonito.

Trial series results; Grass Patch, Ballidu, Merredin and Holt Rock

These results are similar to the other trials at Ballidu and Merredin, where the OP variety gave the best yields, oil and gross margin. The trial at Grass Patch was the highest yielding of the series, at 1.6t/ha, and gave the best gross margins and the biggest advantage of OP over hybrid seed (F1 and F2). The same general pattern was repeated at Ballidu (1.2t/ha), Merredin (1.1t/ha) and Holt Rock (600kg/ha).

There was a trend (that is, non significant) of higher yields and gross margin of purchased hybrid seed (F1) over retained seed (F2) at Grass Patch, Merredin and Holt Rock but not at Ballidu.

Table 3 Yield, oil and gross margin losses averaged over Grass Patch, Ballidu and Merredin trial sites in 2015
  Purchased hybrid (F1) vs retained hybrid (F2) OP vs purchased hybrid (F1) OP vs retained hybrid (F2)
Grain yield (kg/ha) 80 215 300
Oil (%) 1% 1.5 2.5%
Gross margin ($/ha) $17 $150 $167


The highest gross margins were from the open pollinated variety at the higher target density (40 plants/m2). Growers should continue to use open pollinated TT varieties in the low rainfall regions, rather than hybrid varieties.

Where growers in the low rainfall regions choose to grow hybrid varieties, expect a yield and oil advantage and possibly a small gross margin advantage from using purchased (F1) seed, rather than retained (F2) seed. It is recommended that growers purchase fresh (F1) seed, rather than retaining seed.

At Grass Patch and Merredin, agronomy reduced the yield penalty from growing retained (F2) seed, compared with the purchased (F1) seed. Where growers choose to retain hybrid varieties, grade to increase seed size and target high plant density.


This trial (15ME25) part of the ‘Tactical Break Crop Agronomy in Western Australia’ project, which is jointly funded by DPIRD and GRDC.

Thanks to the Merredin RSU for trial management. Laurie Maiolo (DPIRD Merredin) provided technical assistance to ensure all treatments and measurements occurred in a timely and accurate fashion.

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