Canola response to plant density at Grass Patch, 2013 trial report

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 risky 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 OPs 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 OP’s 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 OP’s the crop gross margins may be more sensitive to variations in density.

Acknowledgements

This trial (13ED08) is one of a series conducted throughout WA as part of the GRDC/DPIRD co-funded project 'Tactical Break Crop Agronomy in Western Australia' (DAW00277). 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.