Canola agronomy – consistent messages on canola agronomy hold strong in a Decile 1 season

Take home messages

• Ensure flowering date is matched to the environment and grow enough biomass for the targeted grain yield.
• High biomass was necessary for a high yield potential. There is no advantage in utilising management strategies that reduce growth in order to increase harvest index and grain yield.
• Select two or three varieties with differing phenology or one single variety with flexible phenology to capitalise on variable sowing opportunity dates.
• Early sowing of slow developing spring canola varieties was successful in experiments in 2018 but is best suited to eastern regions with a higher frequency of late March to mid-April rainfall.
• The performance of hybrid canola continues to improve across all herbicide tolerance groups and across diverse environments.
• Nitrogen (N) response was modest in 2018 due to lower grain yield potential. Choosing a paddock with high starting N levels reduces the risk in growing canola in dry seasons as large upfront inputs of N are not required.

Introduction

The consistent recommendations from the Optimised Canola Profitability (OCP) project to date have been:

• Ensure canola flowering date is matched to the environment (i.e. target optimal flowering times as outlined in 10 Tips to Early Sown Canola)
• Maximise the conversion of plant available water into crop biomass using tactical management of sowing date, hybrids and N.

With low in-crop rain and frosts across southern NSW, 2018 was the year to put the system to the test, particularly point 2. The 2018 season more than reinforced the above recommendations – it gave full confidence that the recommendations will hold over highly variable and risky seasons.

Matching flowering date to the environment is an ongoing challenge as the date of the autumn break is highly variable. Based on the sowing rule developed by Unkovich et al.(2015), 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 43% chance in the second half of March at Wallendbeen and a 41% chance in the first half of April. Therefore, sowing opportunities will influence varietal phenology choice. There are only limited opportunities to sow a slow or mid-slow canola variety before mid-April at Condobolin, therefore fast or fast-mid varieties are recommended. At Wallendbeen, there would likely be a more than 50% chance of canola before mid-April, therefore the slow and slow-mid varieties should be considered.

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 1. 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 et al. 2015).

To ensure flowering date targets are met, while also responding to variable seasonal breaks, growers need to either

• have access to two or three canola varieties with contrasting phenology (e.g. a slow and a fast-mid) or
• select a canola variety with relatively flexible phenology, specifically a variety that is relatively slow from early sowing, but faster from later sowing – some examples of these are highlighted below.

2018 phenology results

To determine the phenology of recently released canola varieties, a phenology experiment was established at Wagga Wagga in 2018 with 30 spring varieties sown in late March and early May and three winter varieties sown in late March only. The early sowing was done following 7mm of rain and was provided with an extra 7mm through dripper lines to ensure even establishment. There was approx. 100mm plant available water in the soil at sowing and 160mm rainfall from April to October.

There were subtle development differences between the winter varieties. Phoenix CL was slightly quicker to flower than the more widely grown Edimax CL and Hyola®970CL (Figure 1). There was still a large gap (32 days) in flowering date between the fastest winter variety (Phoenix CL) and the slowest spring variety (Victory 7001CL).

There were also large differences in the development of the spring varieties, particularly from early sowing. Fast varieties included Hyola®350TT, Hyola®506RR, ATR Stingray Diamond and 43Y23 (RR). In 2018, early sowing of these fast varieties resulted in early flowering and significant frost damage, with a resultant machine harvest yield of <0.5t/ha. However, commercial varieties that were relatively slow from early sowing included 45Y25 (RR), 45Y91 (CL), Victory 7001CL, InVigor® 5520P, ATR Wahoo, GT-53 and SF Ignite. These varieties yielded in a range from 1.1t to 1.7t/ha from early sowing. The fast varieties had higher yield sown in early May, while the slow varieties had reduced yield from later sowing (1-1.4t/ha vs 0.4-0.8t/ha).

A key tactic to stabilise flowering date across and within seasons is to select a variety 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 varieties to yield >1t/ha from both sowing dates.

Figure 1. Phenology (start of flowering) of 30 spring varieties from two sowing dates and three winter varieties from one sowing date at Wagga Wagga in 2018.

2018 biomass results

A continuation of the ‘Biomass’ series of experiments at Wagga Wagga (with a combination of two sowing dates, two N rates and eight varieties) reinforced the recommendations of the OCP project. High biomass (combination of early sowing and hybrids) was necessary to generate a high yield potential, but optimising flowering date was important to realise the potential yield. For example, Diamond sown on 4 April produced similar biomass as 4 April sown 45Y91 (CL) (approx. 11t/ha), but Diamond flowered in mid-July, one month before 45Y91 (CL) and yielded 30% less (1.7t/ha vs. 2.6t/ha) due to frost damage. Diamond produced only 7t/ha biomass from the 27 April sowing date, but flowered in mid-August, and with less frost damage yielded 1.9t/ha. There was no response to increasing N from 30kg to 180kg/ha as the starting soil N at the site was 227kg/ha. This highlights the value of stored N for canola, reducing the risk of applying high rates of N early in the season.

Figure 2. Relationship between maturity biomass and grain yield at Wagga Wagga in 2018. Treatments with high biomass, but relatively low grain yield, were generally early flowering and damaged by frost.

A comparison of similar phenology pairs of hybrid Clearfield® and open-pollinated (OP) triazine tolerant (TT) varieties sown within their highest yielding window highlighted the advantages of hybrids even in a very dry year. On average, the hybrid Clearfield® varieties yielded 40% more than the OP TT varieties (Table 2) largely due to their higher biomass.

Table 2. Comparative yield of canola phenology pairs (hybrid Clearfield® versus OP TT) from their highest yielding sowing date at Wagga Wagga in 2018 (l.s.d. P<0.05 = 0.32t/ha).

High yielding canola

Over the past two seasons, a collaborative project (NSW DPI and GRDC) named ‘High Yielding Canola’ has been running in southern NSW, aiming to determine management strategies to achieve 5t/ha canola. One site has been at Wallendbeen with 210mm in-crop rainfall (April to October) and approx. 120mm plant available water at sowing in 2018. The second site has been at Leeton, which has been fully irrigated.

In 2018, highest yields came from sowing spring hybrid canola varieties, with lower yields from the winter varieties at both sites. The hybrid varieties 45Y25 (RR) and 44Y90 (CL) were on average 28% and 19% higher yielding than the OP TT varieties with matching phenology, ATR Bonito and ATR Wahoo, respectively.

In an adjacent trial at Wallendbeen, an extra 100mm of irrigation was applied to 45Y25 (RR) to determine the water unlimited yield potential. This resulted in a 9% grain yield increase compared to the non-irrigated 45Y25 (RR), suggesting that even in a relatively dry year, management factors such as variety choice (especially hybrids vs. OP TT) can have a larger impact than rainfall quantity.

Table 3. Grain yield of 11 canola varieties sown at their recommended sowing date at Wallendbeen in 2018 (l.s.d. P<0.05 = 0.44t/ha) and Leeton (l.s.d. P<0.05 = 0.76t/ha) in 2018.

Conclusion

A very dry 2018 (Decile 1 in-crop rainfall) did not alter the consistent messages from the OCP project. Matching flowering date to the environment and generating as much growth as necessary for the target yield is important to maximise grain yield. Where the date of the autumn break is highly variable, it is recommended to select more than one canola variety, each with differing phenology, or select a variety with flexible phenology. Early sowing of mid and slow spring varieties was successful in 2018 as they generated high biomass and delayed pod-fill till after the severe frosts. This strategy should especially be considered by growers in the eastern part of southern NSW where autumn rainfall is higher, especially those with management practices (stubble retention and strict fallow management) that maximise seedbed moisture retention.

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. Thanks to Cameron Hazlett (Wallendbeen) for cooperation with the 2018 site. Thanks also to technical staff, especially Danielle Malcolm, John Bromfield, Warren Bartlett and Daniel Johnston for assistance throughout.

References

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

Further Reading

https://grdc.com.au/10TipsEarlySownCanola

Contact details

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