Canola – critical agronomy for optimal canola growth

Take home messages

• Time of sowing experiments demonstrated benefits from matching sowing date to variety phenology.
• Optimal start of flowering time provides a target range for flowering to start within, to minimise frost/heat/water stress and maximise yield for a particular environment.
• Once the development triggers/phenology for a variety are understood an optimal sowing date can be derived to match the optimal flowering time.

Background

Research to better understand the yield drivers of canola in eastern Australia commenced in 2014, with the aim to improve canola profitability through gaining a better understanding of how phenology and environment can be best matched to improve canola yields. This research is targeted at low to medium rainfall zones of eastern and southern Australian cropping regions and is a collaboration between CSIRO, NSW DPI and GRDC, in partnership with SARDI, CSU, MSF and BCG (CSP00187). The project links closely with similar GRDC supported projects in Western Australia and high rainfall zones (HRZ).

What is phenology

The description of crop growth stages is called the phenology of the plant. The most common and easily recognised canola stages are emergence, green bud, flowering, podding and maturity.

Plants respond to environmental signals such as temperature, to determine when they move from one growth stage to another. At the biochemical level this is caused by specific temperatures inducing the production of specific plant hormones until a critical concentration triggers the change within the plant. A simpler way to think of this is as a biological clock that accumulates average daily temperatures (day degrees) until a specific target (thermal time target) is achieved.

Why would we want to know this?

One of the most important drivers of canola grain yield, determined from four years of experiments conducted by the optimised canola profitability project, is flowering time. It is important that canola flowers within a particular window for a given environment. If it flowers too early canola crops will be exposed to higher frost risk, increased damage from upper canopy blackleg infection and will not have the opportunity to accumulate high levels of biomass (another key driver of canola yield). If the crop flowers too late it will have increased chances of damage from high temperatures and drought stress.

Each canola variety has a set of triggers that drive its development and controls flowering time; thermal time, vernalisation and photoperiodism. Each of the development triggers may play a different role in each variety.

To match a variety with a sowing time in a particular environment and have it flower within the optimum window requires an understanding of the phenology for each different variety.

What are the phenological development triggers?

Thermal time is the method of combining time and temperature into a single number. It is the average temperature recorded during a day (daily maximum temperature + daily minimum temperature/ 2). To calculate the thermal time target for a plant’s development stage the day degrees are accumulated until a specific target is reached, e.g. variety X accumulates 500 degree days between emergence and flowering. Day degrees are the units of a plants biological clock.

Vernalisation can be described as a low temperature promotion of flowering. Winter wheat and winter canola are extreme examples of plants with vernal requirements. However, many spring wheats and canola varieties can also display a vernal response. These varieties when grown in Victoria can be short season, but if moved to Queensland or planted earlier than usual become longer seasoned, this is due to the difference in rate of vernal day accumulation.

Photoperiodism, is the response of plants to increasing or shortening day lengths. Canola is a long day plant and responds to increasing day length.

Optimum start of flowering

Following four years of field experiments and considerable effort to improve simulated modelling in APSIM®, the Optimised Canola Profitability project has been able to identify the optimum start of flowering date* for canola so that yield is maximised and so that frost, heat and water stress are all minimised. This information has been used in conjunction with historical meteorological records to produce an optimum start of flowering date (and acceptable range – in days) for a number of South Australian localities (Table 1).

Table 1. Optimum start of flowering date* for 13 localities in South Australia (Modelling conducted by Julianne Lilley, CSIRO, Canberra).

*start of flowering is defined as when 50% of plants have one open flower

This information can now be used to extrapolate when a particular canola variety should be sown to maximise yield and minimise environmental stresses (based on historical information). However, this requires an understanding of the development triggers/ phenology for each variety, particularly in early sowing situations. Table 2 provides some of this information based on measurements and observations by the Optimised Canola Profitability project across south eastern Australia over recent years.

Table 2. Proposed ‘phenology ratings’ of canola varieties compared with commercial ‘maturity’ ratings.

Twenty-two canola varieties (Table 2) were included in the Optimised Canola Project from 2014 to 2016. Phenology differences between varieties were a major yield determinant in the project, however phenology did not relate to commercial maturity ratings for early sowing. The project committee is encouraging industry to adopt more accurate phenology terminology as described above to guide sowing date decisions and target the Optimal Start of Flowering period.

Other/newer varieties are available that may also be suited to early sowing, including those indicated above (*).

Matching variety to sowing date

Now that flowering time is known to be an important driver of yield and that each environment has an optimum flowering time window and each variety has a number of drivers that influence when it will flower; the next step is to be able to predict when a variety will flower from a given sowing date in a certain environment. This is possible using historical climatic data and variety phenology information (Figure 1).

Figure 1. Relationship between modelled flowering time of a fast and mid variety on sown 15 April and 10 May at Riverton compared to optimal start of flowering window.

Figure 1 compares the modelled predicted flowering time of two varieties with different phenology; a fast and mid variety when sown 15 April and 10 May at Riverton. When the fast variety is sown on the 15 April it will almost always begin flowering too early to maximise yield potential, but when sowing is delayed until 10 May flowering will always begin in the optimal window. Conversely when the mid variety is sown 15 April it will flower in the optimal window most years, but when sown on 10 May modelling indicates that it will commence flowering too late to maximise yield.

Conclusion

Time of sowing experiments have demonstrated benefits from matching sowing date to variety phenology. Optimal start of flowering time provides a target range for flowering to start within to minimise frost/heat/water stress and maximise yield for a particular environment. Once the development triggers/ phenology for a variety are understood an optimal sowing date can be derived to match the optimal flowering time.

Useful resources

GRDC Southern Canola GrowNotes^TM

GRDC 10 Tips foe Early Sown Canola

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.

This work is a component of the 'Optimised Canola Profitability' project (CSP00187), a collaboration between NSW DPI, CSIRO and GRDC in partnership with SARDI, CSU, MSF and BCG. The author would specifically like to acknowledge the contributions of Rohan Brill (NSW DPI) and John Kirkegaard, Julianne Lilley and Jeremy Whish (CSIRO) for their contribution in developing much of the information reported here.

Thank you to the numerous South Australian growers and Hart Field Site group for making their land available for the field trials and to the technical officers of the SARDI New Variety Agronomy group for their assistance in conducting the field trials.

Contact details

Andrew Ware    
18 Hindmarsh St, Port Lincoln SA 5606
0427 884 272
andrew.ware@sa.gov.au