Profit and risk optimisation in canola – linking physiology and tactical agronomy

Take home messages

• Know the optimum start to flowering time for your location, and match variety phenology with a sowing date to achieve it. See GRDC's publication '10 Tips to Early Sown Canola'
• Early sowing of slow developing spring canola has been successful in the tough years of 2017 and 2018, and suits areas with late-March to early-April sowing opportunities
• Early-sown hybrid varieties with robust N have performed well in 2017 and 2018 despite fears of excessive biomass, rapid water use and yield loss – the opposite has been the case.
• Profitability and risk management in canola is underpinned by sound systems agronomy – especially summer fallow management to conserve water and facilitate timely sowing, and attention to crop nitrogen requirements.

Introduction

The Optimised Canola Profitability Project has been working across eastern Australia for 5 seasons (2014 to 2018) to develop profitable tactical agronomy advice for canola based on a better understanding of the physiology and phenology of canola. We have presented the outcomes at many previous GRDC Updates (see reference list), but 2017 and 2018 have provided challenging conditions to put the outcomes of our work to the test.  In general, the advice we have developed and tested over the years has held up, and in this paper we outline the physiological research that underpins our tactical agronomy advice, and provide examples and recommendations related to central west NSW.

Know your optimal flowering periods

In every location there will be an optimal period for canola to commence flowering that minimises the combined risks of too little biomass or frost (if flowering too early), and heat and water stress (if flowering too late).  Our team has identified the critical period when canola yield is most affected by these stresses (around 300-400 ^oC days after flowering starts).  By combining this knowledge with weather data at specific sites, we have been able to identify the best time for canola to start flowering to minimise these risks and maximise yield (Table 1).  Full information is available in the GRDC E-booklet '10 Tips to Early Sown Canola' but a few sites are shown below.

Table 1. Recommended optimum start of flowering (OSF) dates at selected sites to minimise the combined risk of frost, heat and drought.  The start of flowering is defined as 50% of plants with one open flower.  The range provided assumes the optimum date is the midpoint (i.e. for Trangie 13 days before or 13 days after 26 July is an acceptable start date).

In northern frost-prone environments the later end of the OSF period should be targeted and crops sown on good soil moisture to reduce heat and drought risk.  In medium and high rainfall environments in high canola intensity areas, targeting the later end of the OSF will also reduce risk of upper canopy blackleg and sclerotinia (see '10 Tips to Early Sown Canola').  In the experimental series throughout 2017 and 2018 and across all sites, yield was optimised in crops that flowered close to the optimum start of flowering date (OSF).

Understanding drivers of phenology to match variety phenology to sowing dates

In order to determine when different canola varieties should be sown to achieve the OSF, it was necessary to understand how each variety reacted to the drivers of canola development – temperature, day-length and vernalisation (cold).  Our team has used detailed sites at Canberra (cold) and Gatton (warm) over two years with lights to extend day-length, as well as controlled temperature cabinets to fully understand how current Australian canola varieties respond, and to recommend sowing dates in each environment that will achieve optimum flowering time.  These recommendations have been validated across the experimental series, including all new varieties released in 2018.  A selection of sites for central west NSW are shown in Table 2, but the full information is available in the Ebooklet '10 Tips to Early Sown Canola'.

In experiments specifically designed to reveal which canola varieties may be suitable for earlier sowing, large differences in the development of the spring cultivars were revealed. Fast cultivars unsuited to early April sowing included Hyola® 350TT, Hyola 506RR, ATR Stingray, Diamond and 43Y23 (RR)®. At Wagga Wagga in 2018, early sowing of these fast cultivars resulted in early flowering and significant frost damage, with a resultant machine harvest yield of <0.5 t/ha. The fast cultivars did better from early May sowing.  Commercial cultivars that were relatively slow developing from early sowing included 45Y25 (RR)®, 45Y91 (CL)®, Victory® 7001CL, InVigor® 5520P, ATR Wahoo, GT-53 and SF Ignite. These cultivars yielded in a range from 1.1 to 1.7 t/ha from early sowing but had reduced yield from later sowing.

A key tactic to stabilise flowering date across and within seasons is to select a cultivar that slows its development when sown early, but then speeds up when sown later, providing a relatively stable flowering date despite different sowing dates. The best examples of this “flexible” phenology were 44Y90 (CL)® and 44Y27 (RR)® which, along with HyTTec® Trophy, Quartz and 43Y92 (CL)®, were the only cultivars to yield >1 t/ha from both sowing dates.

Table 2. Recommended sowing dates at three sites in CWNSW for different canola phenology types (slow, mid, fast) to achieve optimum flowering dates.  For the phenology types of current varieties see full details at '10 Tips to Early Sown Canola'.  The 'X' is preferred sowing date, the dash symbol (-) is earlier or later than optimal.

The frequency of early sowing opportunities

The ability to capitalise on early sowing opportunities will depend on the location and soil type which determine how often sufficient rainfall for a successful establishment opportunity occurs.   The frequency of sowing opportunities for a range of sites in southern and central NSW are shown in Table 3.  Based on the sowing rule developed by Unkovich(2010), there is a 22% chance of having enough seedbed moisture to germinate canola in the second half of March and a 17% chance in the first half of April at Condobolin. In contrast there is a 33% chance in the second half of March at Canowindra and a 31% chance in the first half of April.  These sowing opportunities will influence varietal phenology choice. There are limited opportunities to plant a slow or mid-slow canola cultivar before mid-April at Condobolin, therefore fast-mid cultivars are recommended as these perform well from late-April/early May sowing but have some flexibility if there is an early break.  At Canowindra the chances are >50% so the slow and slow-mid cultivars should be considered.  To ensure flowering date targets are met while also responding to variable seasonal breaks, growers can either (i) have access to two or three canola cultivars with contrasting phenology (e.g. a slow and a fast-mid) or (ii) select a canola cultivar with relatively “flexible” phenology, which is relatively slow from early sowing, but fast from later sowing - which we have identified in our recent experiments.

A combination of strict fallow management and maintenance of even residue cover will increase the chance of establishing canola successfully in any window. Conversely, poor summer weed control, overgrazing, cultivation and early stubble burning will decrease the chances of successful early establishment.

Table 3: Chance (%) of a canola sowing (germination) opportunity within defined date ranges in autumn in southern NSW. A sowing opportunity is defined as when rainfall > pan evaporation
in a 7 day period (Unkovich 2010).

Capitalising on earlier sowing systems

Canola is a crop that is known to benefit in both yield, oil, and water-use efficiency from earlier sowing, provided a variety is chosen that achieves the optimal flowering date (Kirkegaard et al., 2016).   However, at the beginning of the project, there was concern that early-sown hybrid varieties with robust N may grow too much biomass, run out of water and perform poorly.  During the course of the project, we have clearly demonstrated that this has not been the case - even in the tough seasons of 2017 and 2018, and across a wide range of environments, hybrid varieties sown early with robust N nutrition (assuming crops need a total of 80 kg N/t of expected yield from soil and fertiliser) have generated more profitable outcomes than later-sown OP-TT varieties – when both flower in the OSF.  The capacity to cover the soil early to reduce evaporation, produce higher biomass at flowering to support a higher yield, and grow deeper roots to access the deeper water in dry springs all contribute to the improved performance of early sown crops.  At Greenethorpe in 2018 hybrid canola sown on 4 April had roots 1m deeper (3.2 m) than that sown on 7 May (2.2m) and the deeper roots were able to capture an extra 35 mm of water from the soil.

A comparison of similar phenology pairs of hybrid Clearfield® and open-pollinated triazine tolerant cultivars sown within their highest yielding window highlighted the advantages of hybrids with adequate N.  At Condobolin, where supplementary water provided a total of 334mm of in-crop rainfall, the hybrid Clearfield cultivars yielded 25% more than the open-pollinated triazine tolerant cultivars (Table 4).  At Wagga Wagga the advantage was 40% and across the 18 sites in 2018 with a wide range of yields (0.5 to 4 t/ha) this advantage was evident and most pronounced at sites with high starting water and low in-crop rainfall, a regular feature in the CW.

Table 4. Comparative yield of canola phenology pairs (hybrid Clearfield (CLF) versus open-pollinated triazine tolerant (OP TT)) from their highest yielding sowing date at Condobolin in 2018
(l.s.d. P<0.05 = 0.32 t/ha).

Getting the system right

In NSW during 2017 and 2018, extreme weather conditions made it difficult to grow canola profitably, yet there were crops that yielded around twice as much as others in the same landscapes. Generally, where a sowing opportunity did occur, these more profitable crops had some consistent features in their pre-crop and in-crop management. The keys to success were:

1. Strict fallow weed control that conserved soil moisture from late spring and summer rain.
2. Evenly spread straw at harvest, minimal stubble grazing to maintain and preserve seedbed moisture to provide timely and successful establishment.
3. Selection of paddocks with relatively high starting soil water and nitrogen.
4. Matching variety phenology with sowing date to ensure flowering starts close to the optimum start of flowering (OSF) to minimise stresses and maximise yield.
5. Sowing hybrid canola (although this alone did not guarantee success).
6. Application of sufficient nitrogen to match grain yield potential.
7. Some luck with timely rainfall, or elevated locations with reduced frost damage.

If the points above (especially 3-5) can’t be achieved, then it may be better to leave the canola seed in the bag to be planted in a season when conditions are more suitable.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the author would like to thank them for their continued support. The projects supporting this research are co-investments from GRDC, NSW DPI, CSIRO and SARDI, and I acknowledge and thank the whole OCP experimental teams.

References

Unkovich M (2010) A simple, self-adjusting rule for identifying seasonal breaks for crop models. Proceedings of 15^th Australian Agronomy Conference 2010, Lincoln, New Zealand.

Kirkegaard et al. (2016) Re-evaluating sowing time of spring canola (Brassica napus L.) in south-eastern Australia – how early is too early?  Crop and Pasture Science 67, 381-396.

Further Reading

'10 Tips to Early Sown Canola'

AusCanola 2018 - 20th Australian Research Assembly on Brassicas (Perth)

Contact details

John Kirkegaard
CSIRO Agriculture and Food
GPO Box 1700, Canberra ACT 2601
Ph: 0458354630
Email: john.kirkegaard@csiro.au

Rohan Brill
Wagga Wagga Agricultural Institute
Ph: 02 6938 1989
Email: rohan.brill@dpi.nsw.gov.au

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