Getting the most from your canola

Damian Jones,

DPI Kerang

Keywords: canola, irrigation, variety

Take home messages 

• Make sure the crop is in on time – late April to early May.
• Get the required number of plants established – around 50 plants/m².
• Make sure the crop has adequate nutrition.
• Control weeds.
• Use some sort of moisture monitoring to ensure the crop has adequate moisture.
• Windrow on time to minimise shattering losses.

Irrigated Canola 101

The team at DPI Kerang have been sowing canola variety trials for many years. 2007 to 2010 saw the trials average 4 t/ha or greater, with a couple of varieties exceeding 5 t/ha. So what do we do to get these results?

Getting good information on varieties is a bit more difficult for canola. Varieties tend to come and go much quicker than the cereals, which makes it difficult to build a picture of the long term yield performance. Variety performance is evaluated under irrigated conditions each year at the ICC Trial Block.  However, the range is limited to the early-mids to mid-late varieties as the trial cannot have too great a range of maturities as this would be too difficult to windrow at a time to suit all varieties. As a very rough guide to performance, the conventionals yield the best, followed by the Clearfields and Roundup Readies and then the Triazine Tolerants. Of course there are varieties in each group that yield better or worse than some in other groups, but this is a general guide and does not take into consideration the opportunities a herbicide tolerant variety may offer in weed control.

Table 1 presents a summary of the top three yielding varieties and their maturity from the trials from the ICC Trial Block.  Table 2 summarises the yield performance of the varieties sown in the ICC Trial Block irrigated canola trial relative to the yield of AV Garnet. 

Table 1: Highest yielding varieties and the maturity group

Table 2: Variety yield performance from the ICC Trial Block relative to the yield of AV Garnet

One aspect of the canola trials that has changed over the years is the move to earlier sowing dates. The aim is to get the trials sown around ANZAC day. This gives the trial a couple of advantages; one being that the soil and weather are a bit warmer allowing the crop to get established before the cold of winter sets in and the second being that flowering is a bit earlier, and therefore, hopefully will avoid high temperatures during flowering and early pod fill.

Aiming at a sowing date is one thing, but having a successful germination and establishment is another. We have had the most success with watering up after sowing. This works on our soil as we can irrigate reasonably quickly and have minimal surface crusting. Some years have seen the bays pre-irrigated, sown and then rely on rainfall for enough moisture for germination. From this experience, relying on rainfall has been the greatest downfall. In 2006 and 2010 (and possibly 2012) this strategy has failed with predicted rainfall not eventuating resulting in poor establishment and subsequent poor yields (2.04 and 2.7 t/ha).

What do we consider poor establishment? The target plant population is 50 plants/m². This is at the lower end of the CanolaCheck recommendation, but it has worked for us. The poor yield results came from populations of in the 20’s, although the 2008 trial (with an establishment of 35 plants/m²) averaged 4.0 t/ha. I think some of the yield decline could be attributed to the lack of moisture that creates poor conditions for germination, followed by slow crop growth.  Too high a population is wasted seed and increases the risk of lodging.

The sowing rate we use to get 50 plants/m² is between 3-4 kg/ha. If conditions are ideal, the 3 kg/ha rate is used. If conditions are not ideal (i.e. lack of moisture, cloddy seedbed, potential for crusting etc), then the rate goes up. Seed size also influences the rate as larger seeds results in fewer seeds per hectare being sown.

Weed management is critical for a high yielding crop and there are three components to good weed control; controlling the weed seedbank prior to the crop (eg a hay crop), good establishment and vigorous crop that is able to compete with the weeds and keeping a close eye on the crop and spraying on time to ensure the weeds don’t get a hold.

Nitrogen management follows our recommended practice of calculating the N budget for the crop. The N is applied via the “canopy management” method of limiting early N and applying it to the crop when it is needed, i.e. for stem elongation or bolting.

Deep soil N tests, either pre-sowing or in-crop, are essential to accurately determine the level of soil N in the paddock. At sowing, starter N is applied, in our case as 125 kg/ha DAP (approximately 25 kg N/ha) and we would expect the breakdown of organic matter throughout the season to produce another 60 kg N/ha. Previously we were using the assumption that canola required 80 kg N/ha per tonne of grain. However, trial work and observations from the ICC Trial Block have shown us that this figure is closer to 60 kg/t of grain. Our usual yield target is 3.5t/ha and a crop of this yield potential would need 210 kg N/ha. After adding up what we have (soil N + starter N + mineralised N) we then know what the deficit (if any) is and topdress accordingly.

E.g. for the 2007 season

N required:      3.5 (t/ha) x 60 = 210 kg N/ha

N we have:      45 (soil) + 25 (starter) + 60 (mineralised) = 130

Therefore we were 80 kg N/ha short.

This shortfall is usually supplied as a split topdressing, typically around mid July (cabbaging) and mid August (mid bolting/prior to flowering). Similar to the cereals, canola has its main requirement for nitrogen at the stem elongation/bolting stage. However this strategy relies on topdressing and moisture to wash the N into the rootzone, not only to minimise N volatilisation when using urea, but to get it to the roots for the crop to use. Not all seasons provide rain at the right time but there is a degree of flexibility in these timings.

Our decision to split topdress is based on the usual need to supply relatively large amounts of N to the crop and an effort to make sure our topdressing is even. In paddocks where the N levels were higher, then obviously the required amount of N would be reduced and therefore the risk in a single topdress is reduced.

Of course, don’t forget adequate P (a minimum of 6 kg P/t or 21 kg P/ha in the above example) and S (3.5 kg S/t or 12 kg S/ha).

Irrigation management is also critical to success. Sam North, a hydrologist with DPI NSW at Deniliquin, has recently completed his thesis on canola irrigation. His conclusions include the necessity to pre-irrigate to ensure you have a crop with good yield potential, and then the first spring irrigation should be around early flowering as this ensures pod set which is the major driver of yield. Later irrigations increase seed size but if irrigation is delayed, the potential yield has already been reduced.

At the trial block, soil moisture monitoring equipment is used to objectively measure the soil conditions and combined with the crops growth stage, used to make decisions on irrigation. Irrigation is usually at the beginning of flowering and at the end of flowering. Our soil holds approximately 75mm of available water which is enough to keep the crop happy over this period.

Another conclusion Sam drew is that canola is not as capable as the cereals at accessing moisture in soils that have dense subsoils and so should be irrigated earlier compared with the cereals.

While we have a certain amount of control over the above, we cannot control the weather and in particular, the temperatures we get in spring. Some seasons see the flowering of canola cut short by hot windy days in late September or early October. The seasons where we have had good yields have tended to be those where the spring had no extremes during flowering and pod fill.

Summary

The yields achieved are due to a combination of good management with some favourable weather conditions at the critical late flowering and pod-fill period. However we do have some influence in trying to make sure the crop has the optimal conditions to achieve its potential by getting the basics right:

1. Make sure the crop is in on time – late April to early May.
2. Get the required number of plants established – around 50 plants/m².
3. Make sure the crop has adequate nutrition.
4. Control weeds.
5. Use some sort of moisture monitoring to ensure the crop has adequate moisture.
6. Windrow on time to minimise shattering losses.

Contact details

Damian Jones

DPI Kerang, 26 Wellington St
Damian.Jones@dpi.vic.gov.au