| 30 April | 15 May | 30 May | 15 June | 30 June | |
|---|---|---|---|---|---|
| LRZ | 10 | 20 | 25 | 20 | 15 |
| MRZ | 5 | 20 | 30 | 25 | 20 |
| HRZ | 0 | 10 | 20 | 30 | 30 |
The cumulative per cent yield loss for delay in sowing compared to the sowing time with maximum yields is presented in Table 3. If sowing is delayed until the end of May, APSIM estimated a cumulative per cent yield loss of 47% in the low rainfall locations and only 15% in the high rainfall locations.
| 30 April | 15 May | 30 May | 15 June | 30 June | |
|---|---|---|---|---|---|
| LRZ | 8 | 26 | 47 | 64 | 76 |
| MRZ | 4 | 18 | 36 | 55 | 68 |
| HRZ | 1 | 5 | 15 | 30 | 46 |
The yield loss for delay in sowing can also be expressed as the percentage of years achieving a certain yield by certain sowing dates (Figure 3). For example, in Mingenew, there is a reasonable chance (90%) of getting 1.0t/ha when sowing between mid-April and mid-May, but this is reduced to around 60% for sowing at the end of May (Figure 3). This is based on last 41 years of climate data. Figures for the 24 locations studied can be found in this link.
How late is too late to sow canola?
Answering this question depends on:
- Stored soil moisture – depends on rainfall to date and soil type
- On-time yield estimate - average from past 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
Canola
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.
Wheat/barley
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 following season.
Pulses
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.
Fallow/pasture
Leaving this paddock to fallow or pasture may not have been what was planned for the season, but will leave the paddock well set up for a more promising start in the following season. A fallow will store future moisture and nutrients as well as giving a disease and weed break. Legume pastures will put the paddock ahead for nitrogen in the following season and topping any pasture will put the paddock ahead for weed control.