Results
Grain yields of most canola varieties at Salmon Gums started to plateau at ~ 20 plants/m2 (Figure 1). Taking into account the costs of increasing plant density we calculated the economic optimum for higher cost seed types such as RR and hybrid TT to be 25 plants/m2 or less. Hyola 404RR had the flattest response indicating its yields were less affected by lower plant densities.
CB Telfer was the lowest yielding variety at Salmon Gums in 2013, which may be attributed to its earlier maturity not making use of late spring rains to the same degree as other varieties. In spite of a long slow increase in yield with increasing plant density, the low cost of seed for CB Telfer ensured a slighter higher economic density of 31 plants/m2.
Hyola 450TT was the highest yielding variety at Salmon Gums and produced the highest gross margins of $473/ha. Gross margins of all other varieties were in the range of $343-$379/ha (averaged over densities).
| Location | CB Telfer or ATR Stingray | Hyola 450TT | GT Viper | Hyola 404RR | Comments |
|---|---|---|---|---|---|
| Cunderdin | 25 | 22 | 28 | 17 | No comments |
| Eradu | 34 | 33 | 24 | 16 | No comments |
| Grass Patch* | 53 | 71 | 53 | 41 | Low density treatments targeted by birds |
| Holt Rock | 39 | 20 | 30 | 38 | No comments |
| Katanning | 39 | 24 | 39 | 21 | TT blocks weedier - more ryegrass in low density |
| Merredin | 22 | 20 | 17 | 18 | TT blocks weedier - more ryegrass in low density |
| Miling | 36 | 27 | 20 | 12 | Low establishment, low density = more ryegrass |
| Mullewa | 19 | 12 | 10 | 14 | Extended dry period and aphids |
| Pingrup | 29 | 23 | 19 | 18 | No comments |
| Salmon Gums | 31 | 25 | 22 | 18 | Late emerging barley grass understory in RR blocks |
| Wongan Hills | 40 | 35 | 34 | 21 | TT blocks weedier, more ryegrass in low density |
Conclusion
The economic optimum plant density of canola appears to be different for each type of canola and in some instances may need to be altered for rainfall zones. Open-pollinated TT canola which dominates the WA industry had higher optimum densities primarily because of the low cost of increasing density.
Optimum target densities and suggested seeding rates based on 2013 experiments are:
- OP TT - 31 plants/m2 which equates to a seeding rate of 2.1kg/ha for ATR Stingray and 2.4kg/ha for CB Telfer - but there is no economic reason not to go higher with grower retained seed.
- Hybrid TT - 23 plants/m2 (seed rate of ~ 1.4kg/ha). Using such a low seed rate may be risk so it may pay to increase seed rate if conditions are questionable or machine is not calibrated for low seeding rates.
- OP RR – 24 plants/m2 (seed rate of 2.2kg/ha).
- Hybrid RR - 20 plants/m2 equivalent to a seed rate of ~ 2.1kg/ha. Adjust seed rate for variety/seed lot seed size differences.
Note that all optimum densities calculated here assume a given field establishment of 50% for OP’s and 65% for hybrids and 90% germination test. As observed field establishment rates can vary due to soil moisture, temperature and seeding errors. Similarly seed size may vary from those used in our trials. Grower retained seed of TT OPs in dry areas is often smaller than purchased seed and it is our experience that hybrid seed size varies markedly from year to year. Therefore seed rates should be adjusted to suit individual circumstances. Variations in grain prices, seed size, germination and field establishment may also affect our optimum density calculations, particularly if the calculated optima are not on the plateau of the response curve. In most instances for OP TTs and RR hybrids the calculated optima are on the plateau of the response curve and variations in assumptions and changing crop density will affect gross margins slightly. However for TT hybrids and RR OPs the crop gross margins may be more sensitive to variations in density.
Acknowledgements
This trial (13ED09) 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 Research Support Unit for trial management. Pam Burgess (DPIRD Esperance) provided technical assistance to ensure all treatments and measurements occurred in a timely and accurate fashion.