1. Yield loss from delayed sowing trials in Western Australia
DAFWA development officer Jackie Bucat has compiled data from, and summarised, time of sowing trials for canola in WA (Figure 1).
There are variable yields and variable loss profiles for the start of May.
However, from mid-May onwards, there is a generally a similar rate of loss across most trials.
Overall, the yield loss from delayed sowing is about 15kg/ha/day for the third week of May, up to a peak of 25kg/ha/day for the first half of June.
In general, growers could expect to lose more than half a tonne of yield if sowing is delayed from mid-May to mid-June.
A decrease in oil percent would also be expected, with later sowing time.
|Average loss per day (kg/ha)||Average loss per week (kg/ha)|
|Third week in May||10||70|
|Fourth week in May||15||105|
|First week in June||25||175|
|Second week in June||25||175|
|Third week in June||20||40|
2. APSIM modelling estimates of yield loss for different locations
Localised differences in expected yield and estimated yield loss rates can be shown by computer modelling. DAFWA research officers Bob French and Imma Farre have used Agricultural Production Systems Simulator (APSIM) to model canola yield decline with later time of sowing, for seven locations.
The modelling was done using 2017 rainfall, up until 24 May, then the ongoing rainfall for each of the last 40 seasons. The median results are presented in Figure 2.
These results give an estimation of expected yields, as well as the rate of loss. Differences in the rate of loss between environments is shown, with later peak yield loss in longer season environments (Table 2). During the period 10-20 May, yield losses may be around are 8kg/ha/day at Kojonup but 36kg/ha/day at Mullewa.
If sowing is delayed from 10 May until the end of May, APSIM estimated a cumulative 46% yield loss at Mullewa, but only 9% at Kojonup (Table 3).
APSIM modelling included predicted losses to frost and heat. Variety used for APSIM was ATR Bonito (Kojonup, Esperance, Wongan Hills, Merredin) and Hyola 404 (Mullewa). Single soil type used (shallow sandy duplex).
How late is too late to sow canola?
Answering this question depends on;
- Stored soil moisture - 2017 rainfall included in the APSIM modelling
- On-time yield estimate - best to use average from past ‘normal’ seasons
- Estimated yield loss - as suggested above, balanced with your experience
- Break even yield - essential to know this to make an informed decision
- End of season conditions - much will depend on finishing rains.
Options when considering dropping a canola paddock
If plans were to grow canola as a valuable break crop in your rotation, the best decision may be to go ahead, albeit with a lower profit estimate, to capture the disease/weed control rotation benefit. Minimise inputs and delay nitrogen top up until early flowering, when a better seasonal assessment can be made.
If there is disease or weed pressure building up in the paddock, beware of substituting a cereal crop as the paddock might end up in a worse position for the start of the 2018 season.
Field pea may be a good option for later sowing on heavier soil types, but access to seed and high seed prices make this an unlikely option.
Leaving this paddock to fallow or pasture may not have been what was planned for 2017, but will leave the paddock well set up for a more promising start in 2018. A fallow will store future moisture as well as giving a disease and weed break. Legume pastures will put the paddock ahead for nitrogen in 2018 and topping any pasture will put the paddock ahead for weed control.