Summary
In this 2013 trial:
- Canola yield responded to increasing plant density to 65 plants per square metre (plants/m2) but there was very little response at densities greater than 20-30 plants/m2
- The response was variable within this trial site, which means that is very likely to be quite variable across different years and locations.
- Roundup Ready (RR) canola enabled much better weed control than triazine tolerant canola on this site.
Background
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 in order to get these potential yield benefits. Seed for hybrid canola is 25 times more expensive than the seed of open pollinated canola. If growers decide to grow hybrids they may wish to minimise seed costs by sowing at lower densities.
Aim
To compare the plant density response of yield and oil content between hybrid and open pollinated (OP) canola in Triazine Tolerant (TT) and RR herbicide tolerance groups.
Trial details
| Property | DPIRD Wongan Hills research facility |
|---|---|
| Agzone 2 | Growing season rainfall (GSR) = 249mm, GSR + stored water (estimate) = 286mm |
| Soil type | Loamy sand (1.01% organic carbon), total mineral nitrogen (N) at seeding 52 kilograms per hectare (kg/ha) to 50 centimetres (cm) |
| Paddock rotation | Wheat 2012, Pasture 2009-2011 |
| Replicates | 3 |
| Sowing date | 13 May 2013 |
| Fertiliser | 100kg/ha of Whitgro Extra at seeding, 120kg/ha of Muriate of Potash and 400kg/ha of gypsum (17% Ca, 14% S) topdressed over whole site four weeks after seeding |
| Treatments | 32: 2 herbicide tolerant types (RR and TT) × a hybrid and an OP cultivars within each type (GT Viper and ATR Stingray, OP for RR and TT respectively; and Hyola 404 RR and Hyola 450 TT, hybrid for RR and TT respectively) × 8 target densities (5, 10 ,15, 20, 30, 40, 60, and 80 plants/m2) |
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
- Herbicide costs $28/ha for RR, $47/ha for TT
- RR grain worth $482/t (CBH Pool Kwinana 5 November 2013)
- TT grain worth $495/t (CBH Pool Kwinana 5 November 2013)
Results
Increasing seed rate increased established density
The established densities were on average 86% of the target density. In calculating our seed rates we assumed that 75% of viable seed of TT varieties and OP RR varieties would establish, and 85% of Hybrid RR varieties would establish. The overall establishment efficiencies were 95% for the TT varieties, 90% for Hyola 404 RR, and 64% for GT Viper.
Yield responded to increasing density
All varieties responded to increasing density but the response was very flat at more than 40 plants/m2. There was some evidence of declining yield at high density (the maximum observed in this trial was 86 plants/m2) but it was very slight. The response flattened out at lower densities in hybrids than open-pollinated varieties.
Roundup Ready varieties had much less ryegrass than TT varieties
There was much less ryegrass in Roundup Ready plots than in triazine tolerant plots, especially at low densities. Ryegrass numbers decreased rapidly as crop density increased: TT plots at 30 plants/m2 had twice as many ryegrass heads as at 50 plants/m2. At low densities below 20 plants/m2 the hybrid Hyola 450 TT has less ryegrass than the open-pollinated ATR Stingray.
Conclusion
The density response of open-pollinated canola varieties flattens out at densities above about 40 plants/m² while that of hybrid varieties flattens out at about 30. The density response curve is quite difficult to predict, as is also the establishment efficiency. The establishment efficiency observed in this trial was considerably higher than at some other sites in 2013 using the same seed which underlines the uncertainties involved in choosing canola seed rates. This means that there is always a danger that the target density will not be achieved, and the flatter response of the hybrid varieties can help minimise the adverse consequences of this if it happens. Data from this trial have been used as part of a larger data set to develop some guidelines for choosing canola densities in Western Australia (WA), these overall results were discussed at the 2014 Agribusiness Crop Updates. As well as yield density, plant density can also have profound consequences for weeds. There is a danger of weed blowouts at very low densities, especially if TT varieties are used and there is some herbicide resistance present. Roundup Ready canola proved to be very effective for ryegrass management.
Acknowledgements
This trial (13WH11) is one of a series conducted throughout WA as part of the GRDC/DPIRD co-funded project 'Tactical Break Crop Agronomy'. Thanks to Shari Dougall and Bruce Thorpe of the Wongan Hills Research Support Unit for trial management. Laurie Maiolo (DPIRD Merredin) provided technical assistance to ensure all treatments and measurements occurred in a timely and accurate fashion.