1. Optimum Density for Canola in WA
Optimum Density for Canola in WA. How important is it and what affects it
Bob French
Department of Primary Industries and Regional Development
Merredin WA

2. Background
24 canola cultivar × density trials
2010 to 2014
Funded by a series of GRDC projects, currently “Tactical Break Crop Agronomy in Western Australia”
French RJ, Seymour M and Malik RS (2016). Crop and Pasture Science 67,

3. Analysis
Response curves fitted
Optimum density chosen using simple microeconomic theory
Has semblance of mathematical rigour
French RJ, Seymour M and Malik RS (2016). Crop and Pasture Science 67,

4. The range of optimum densities
Low rainfall
Medium rainfall
High rainfall
RR hybrid
25.3
24.1
34.1
RR OP
26.8
23.0
33.5
TT hybrid
33.0
30.4
36.8
TT OP
77.9
76.2
132.9
Median optimum density for 4 canola plant types across the range of production environments in Western Australia
Distribution of 112 canola optimum densities calculated from 24 genotype × density trials in Western Australia 2010 to 2014

5. Assumptions
Optimum density depends on:
price received for canola produced and seed cost
seed size
germination percentage
field establishment

6. Questions
Two questions:
How much influence do these have?
What are the consequences of getting the optimum wrong?

7. Cost-price ratio
Cost price ratio has a profound effect on canola optimum density, particularly when using low cost farmer retained seed

8. Field establishment
Poor field establishment reduces optimum density but in such a way that optimum seed rate is increased. Very low field establishment for canola is a common problem in all canola growing areas

9. Missing the optimum: hybrids
Gross margin usually reduced by less than $20/ha if achieved density is within 10 plants/m² of the optimum. Penalty for undershooting optimum less more than overshooting by the same amount

10. Missing the optimum: OP
Gross margin is within $20/ha of the optimum up to 50 plants/m² from the optimum for open-pollinated TT cultivars. This depends on using low cost farm-saved seed

11. Key messages
Optimum density varies depending on genetic and environmental factors as well as a range of assumptions
Strongly driven by seed cost: grain price ratio which in the case of canola will depend largely on seed cost.
Field establishment is a serious issue in canola that makes optimum estimates uncertain.
There is quite a large acceptable margin for error in optimum densities, especially when using low cost farm-retained seed.

12. Thank you Visit dpird.wa.gov.au
Important disclaimer The Chief Executive Officer of the Department of Primary Industries and Regional Development and the State of Western Australia accept no liability whatsoever by reason of negligence or otherwise arising from the use or release of this information or any part of it.
Copyright © Western Australian Agriculture Authority, 2017