Background and aim
With the rapid adoption of hybrid technology it is critical to ensure seed costs are minimised by obtaining good establishment rates. In 2015 in the northern agricultural region there was a mid-April season break followed by a month without significant follow-up rain. Temperatures at sowing were above 30°C and the surface soil dried quickly. Many farmers experienced better establishment with canola if they sowed slightly deeper than their normal seed depth. With this in mind we thought it was timely to test how deep canola seed could germinate from and how the seed type (OP or hybrid) and seed size influenced establishment rates when sowing in mid-April conditions.
Trial details
The trial was conducted in the northern agricultural region at Eradu on the Department of Agriculture and Food, Western Australia's (DAFWA) Valentine Road research annex. The soil type was deep yellow sand. The trial was sown with a small plot seeder, plots 20m x 1.54m in area on 13 April The target plant density was 40 plants/m2 using a 65% field establishment rate. This density is higher than recommended for the area however, it was anticipated that the actual field establishment achieved at the 7cm sowing depth would be much lower than 65%.
Treatments
Three treatments were used;
- Seed depth of 1, 3 and 7cm
- Variety: ATR Bonito (OP) and Hyola 559TT (hybrid)
- Three seed sizes
The different seed sizes were obtained by sieving seed from commercially available seed lots. Different sieve sizes were required for each variety to split the original seed lot into size lots with small being ~20% of the original, medium ~60% and large ~20%. For the ATR Bonito sieves were 1.7mm, 1.7-2.0mm and >2.0mm. For the Hyola 559TT sieves were <2.0mm, 2.0mm-2.36mm and >2.36mm.
| Variety | Seed Size | Sieve Size | % of orginal lot | 1000 seed weight (g) | Seed/kg | Seed/plot (g) | Seed #/plot | Seed rate (kg/ha) |
| ATR Bonito | Small | <1.7 | 18 | 2.70 | 370370 | 6.37 | 2494 | 1.75 |
| ATR Bonito | Medium | 1.7-2.0 | 69 | 3.60 | 277778 | 8.98 | 2494 | 2.33 |
| ATR Bonito | Large | >2.0 | 13 | 4.31 | 232019 | 10.75 | 2494 | 2.79 |
| Hyola 559TT | Small | <2.0 | 18 | 4.26 | 234742 | 10.57 | 2494 | 2.75 |
| Hyola 559TT | Medium | 2.0-2.36 | 62 | 6.40 | 156250 | 15.96 | 2494 | 4.15 |
| Hyola 559TT | Large | >2.36 | 20 | 8.17 | 122399 | 20.38 | 2494 | 5.2 |
Results
The long term mean average rainfall for Eradu is 371mm, rainfall in 2016 was slightly below this. The summer period was dry with little rain in February or March, however rain from 8-12 April of 30.4mm meant the trial was sown into moist soil. An inch of follow-up rain occurred on 26 April followed by an extended period without significant rain through early and mid-May. These conditions caused the soil surface to dry whilst seeding however, measurements of soil moisture at the three seeding depths of 1, 3 and 7cm, along with deeper measurements indicated that soil moisture at the top 1cm was similar or greater than at depth in the two weeks following sowing despite hot conditions with ambient temperatures well above 30°C.
| Site | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Rainfall to date |
| Eradu | 42.6 | 0.6 | 0.8 | 49.0 | 33.2 | 70.4 | 77.4 | 13.2 | 57.2 | 8.8 | 1.8 | 0.2 | 355.2 |
Establishment was much lower than targeted with 19 plants/m2 the highest of any treatments and an overall mean of 8.2 plants/m2. This occurred because conditions at seeding were, as previously discussed, not ideal with temperatures above 30°C. While overall establishment was low plant densities followed the expected trends given the seeding depth, plant type and seed size treatments with all main effects highly significant.
| Sowing depth | Seed size | ATR Bonito p/m2 | Hyola 559TT p/m2 |
|---|---|---|---|
| 1cm | Large | 17.2 | 18.2 |
| 1cm | Medium | 13.7 | 19.5 |
| 1cm | Small | 8.6 | 12.0 |
| 3cm | Large | 7.2 | 7.9 |
| 3cm | Medium | 5.2 | 9.4 |
| 3cm | Small | 3.4 | 6.3 |
| 7cm | Large | 2.7 | 4.3 |
| 7cm | Medium | 3.8 | 5.3 |
| 7cm | Small | 0.9 | 5.2 |
| F Prob depth | <.001 |
|---|---|
| Lsd depth | 1.42 |
| F Prob seed size | <.001 |
| Lsd seed size | 1.42 |
| F Prob variety | <.001 |
| Lsd variety | 1.16 |
Site mean yield was 1.32t/ha however the highest yielding treatments produced over 1.7t/ha. Seeding depth had the greatest influence on yield, as expected given the large impact of this treatment on plant density. The 1cm seeding depth averaged 1.7t/ha, 3cm 1.3t/ha and 7cm 1.0t/ha. The Hyola 559TT yielded 1.4t/ha compared to the ATR Bonito 1.2t/ha. The large seed yielded 1.4t/ha, medium 1.4t/ha and small 1.2t/ha and the seed size effect was less for the hybrid. Seed oil percentage was reduced by deeper sowing and by using smaller seed. The size of the seed produced was also reduced by deeper sowing and using smaller seed at sowing. This shows that retaining OP seed should be graded to ensure a gradual decline in seed size over seasons does not occur.
Total seed costs were calculated using cost per kilo for each seeding rate. Seed costs ranged from $127/ha for the large size hybrid seed sown at 5.29kg/ha to $23/ha for the small size open-pollinated seed sown at 1.79kg/ha. Grain prices used were five year averages of non-GM canola worth $543/tonne and GM canola $523/tonne. There was a large range in gross margins from -$138 to $468/ha.
When sown at the sowing depth of 1cm ATR Bonito had higher gross margins than Hyola 559TT, due to similar yields but lower seed costs. It needs to be highlighted that the size of the Hyola 559TT seed in the commercial seed lot used was large at around 180 000 seed/kg. Even the smallest 20% of the hybrid seed lot was quite large seed at 235 000 seed/kg, which explains the lack of response to seed size of the hybrid. This also meant that seed rates/costs were high for the hybrid. As seeding conditions were made more difficult by sowing deeper with small seed, the gross margins of Hyola 559TT were greater than ATR Bonito demonstrating the benefit of the hybrid in more difficult seeding conditions.
Conclusions
Trying to chase deep soil moisture did not work. Even though conditions at seeding in mid-April were hot and drying the 1cm treatments established and yielded better than deeper sowing depths. When canola was sown at 1cm the OP variety ATR Bonito established a reasonable amount of plants and gross margins were higher than hybrid canola due to reduced seed costs. However there was an advantage using hybrid canola and in particular using medium sized hybrid canola when sowing deeper than 1cm. Again the plasticity of the canola plant in the northern agricultural region environment was demonstrated with impressive yields achieved from very low plant populations when sown in April. It highlights that early sowing of canola is critical and to maximise the sowing opportunities more work is required to improve establishment methods in harsh conditions. We intend to continue testing in more controlled laboratory conditions to determine rules of thumb for field establishment rates under different soil temperature and moisture conditions.
Acknowledgements
Thanks to Stephanie Boyce and the Geraldton RSU for trial management and measurements and Bruce Ley for supplying the site. This trial (16GE01) was funded by Department of Agriculture and Food, Western Australia and Grains Research and Development Corporation (DAW00227).