Management of flowering time and early sown slow developing wheats

Take home messages

• Different winter varieties are required to target different optimum flowering windows.
• Best yields of winter wheats sown early are similar to Scepter sown in optimal window.
• If sowing early use the right winter cultivar for the right yield and flowering environment.
• Highest yields for winter wheats come from early – late April establishment.
• Mid - slow developing spring varieties are less suited to pre-April 20 sowing.

Background

Timely operations are key to maximising farm profit, and sowing is one of the most time-critical operations. This is because there is only a short period (approximately 10 days) in spring during which crops can flower and yields be maximised. This period is referred to as the optimal flowering period and its timing and length varies with location and climate. During the optimal flowering period, it’s important that the combined yield loss from drought, heat, frost and insufficient radiation is minimised, and yield maximised. Increasing farm sizes and cropped area and declining autumn rainfall have made it increasingly difficult to get crops flowering during the optimal period.

Sowing early with appropriate cultivars is one management strategy to increase the amount of farm area that flowers during the optimal period and thus farm yield can be maximised. Sowing early requires cultivars that are slower developing to take advantage of early establishment opportunities. They are ideally sown into a moist seed bed following breaking rain or preceding a convincing forecast of enough rain to allow germination. This should not be confused with dry sowing which will typically use fast developing cultivars sown into dry seed beds that will establish when breaking rains fall.

Winter wheats for early sowing

For sowing prior to April 20, winter cultivars are required, particularly in regions of high frost risk. Winter wheats will not progress to flower until their vernalisation requirement is met (cold accumulation) whereas spring cultivars will flower too early when sown early. The longer vegetative period of winter varieties also opens opportunities for grazing. Winter wheat cultivars allow wheat growers in the southern region to sow much earlier than currently practiced, meaning a greater proportion of farm can be sown on time.

Management of Early Sown Wheat experiments

The aim of this series of the GRDC Management of Early Sown Wheat (MESW) experiments is to determine which of the new generation of winter cultivars have the best yield and adaptation in different environments and what is their optimal sowing window. Prior to the start of the project in 2017 the low to medium rainfall environments had little exposure to the new winter cultivars, particularly at really early sowing dates (mid-March). Three different experiments have been conducted in the southern region in the low to medium rainfall environments during 2017 and 2019, including collaboration in NSW for additional datasets presented in this paper.

Experiment 1 - Which wheat cultivar performs best in which environment and when they should be sown

• Target sowing dates: 15 March, 1 April, 15 April and 1 May (10mm supplementary irrigation to ensure establishment).
• Locations: South Australia (SA) - Minnipa, Booleroo Centre, Loxton, Hart. Victoria (Vic) - Mildura, Horsham, Birchip and Yarrawonga. New South Wales (NSW) – Condobolin, Wongarbon, Wallendbeen.
• Up to ten wheat cultivars - The new winter wheats differ in quality classification, development speed and disease rankings (Table 1).

Table 1. Summary of winter cultivars, including Wheat Australia quality classification and disease rankings based on the 2020 SA Crop Sowing Guide.

*Southern NSW only; YLS = yellow leaf spot; Australian Hard (AH), Australian Prime Hard (APH), Australian Standard White (ASW), Australian Premium White (APW); Resistant (R), Moderately Resistant (MR), Moderately Susceptible (MS), Susceptible (S)

Different winter cultivars are required to target different optimum flowering windows

Flowering time is a key determinant of wheat yield. Winter cultivars are very stable in flowering date across a broad range of sowing dates which has implications for variety choice as flowering time cannot be manipulated with sowing date in winter wheats like spring wheat. This means that different winter varieties are required to target different optimum flowering windows. The flowering time difference between winter cultivars are characterised based on their relative development speed into three broad groups; fast, mid and slow for medium to low rainfall environments (Table 1 and Figure 1).

For example at Birchip each winter variety flowered within a period of seven to ten days across all sowing dates, whereas spring cultivars were unstable and ranged in flowering dates over one month apart (Figure 1). In this Birchip example, the fast to mid developing winter wheats with development speeds similar to Longsword and Illabo are best suited to achieve the optimum flowering period 10 September to 20 September for Birchip. In other lower yielding environments such as Loxton, Minnipa, and Mildura the faster developing winter cultivars; ADV15.9001 and Longsword were better suited to achieve the flowering times required for the first 10 days in September. Whereas, Illabo and Kittyhawk were more suited to the Mid North of SA at Hart and Tarlee (Figure 1).

Figure 1. Mean heading date responses from winter and spring cultivars at Birchip in 2018 and 2019 across all sowing times, grey box indicates the optimal period for heading at Birchip.

Best yields of winter wheats sown early are similar to Scepter sown in its optimal window

• Across all experiments the best performing winter wheat yielded the same as the fast developing spring variety Scepter sown at its optimal time (last few days of April or first few days of May, used as a best practice control) in 23 out of 31 sites, greater than in six sites and less than in two sites (Figure 2).
• The best performing winter wheat yielded similar to the best performing slow developing spring variety (alternative development pattern) at 26 sites, greater than at three sites and less than at two sites.

Figure 2. Grain yield performance of Scepter wheat sown at its optimal time (late April-early May) in 28 environments (2017 – 2019) compared to the performance of the best performing winter wheat and slower spring wheat. Error bars indicate LSD (P<0.05).

Table 2. Summary of grain yield performance of the best performing winter and alternate spring cultivar in comparison to Scepter sown at the optimum time (late April-early May). Different letters within a site indicate significant differences in grain yield.

*stem and/or reproductive frost substantially affected yield; #Cultivars ADV15.9001, Trojan and IGW6566 were not included at all sites

The best performing winter cultivar depends on yield environment and development speed

The best performing winter wheat cultivars depended on yield environment, development speed and the severity and timing of frost (Table 1). The rules generally held up that winter cultivars that are well-adjusted to a region yielded similar to Scepter sown in its optimal window. These results demonstrate that different winter wheats are required for different environments and there is genetic by yield environment interaction:

• In environments less than 2.5t/ha the faster developing winter cultivars Longsword and ADV15.9001 were favoured (Table 2, Figure 3).
• In environments greater than 2.5t/ha the mid to slow developing cultivars were favoured; Illabo in the Mid North of SA, and DS Bennett at the Vic and NSW sites (Figure 4).

The poor relative performance of Longsword in the higher yielding environments was explained by a combination of flowering too early and having inherently greater floret sterility than other cultivars irrespective of flowering date.

Sites defined by severe September frost and October rain included Yarrawonga, Mildura and Horsham in 2018. In this scenario the slow developing cultivar DS Bennett was the highest yielding winter wheat and had the least amount of frost induced sterility. The late rains also favoured this cultivar in 2018 and mitigated some of the typical yield loss from terminal drought (for example, Birchip 2019). Nonetheless, the ability to yield well outside the optimal flowering period maybe a useful strategy for extremely high frost prone areas for growers wanting to sow early.

Highest yields for winter wheats come from early to late April establishment

• Across all environments the highest yields for winter wheats generally came from early to late April establishment and results suggested that the yields may decline from sowing dates earlier than April and these dates may be too early to maximise winter wheat performance (Table 2, Figure 3 and Figure 4). The cultivar DS Bennett maintained yield better than other cultivars from March establishment.
• Mid to-slower developing spring wheats (for example, Cutlass) performed best from sowing dates after April 20 and yielded less than the best performing winter cultivars when sown prior to April 20. This reiterates slow developing spring varieties are not suited to pre-April 20 sowing in low to medium frost prone environments.
• The very slow developing spring wheat; Nighthawk yielded similar to the best performing winter cultivar in both yield environments from mid-April establishment dates.

More details on experiment one can be found here:
Management of early sown wheat: matching genotype to environment - James Hunt

Conclusion

Growers in the low to medium rainfall zones of the southern region now have winter wheat cultivars that can be sown over the entire month of April and can achieve similar yields to Scepter sown at its optimum time. However, grain quality of the best performing cultivars is modest (Longsword=feed, DS Bennett=ASW). Sowing some wheat areas early allows a greater proportion of farm area to be sown on time. Growers will need to select winter wheats suited to their flowering environment (fast winter in low rainfall, mid and mid-slow winter in medium rainfall) and maximum yields are likely to come from early to mid-April planting dates.

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 project is led by La Trobe University in partnership with the South Australian Research and Development Institute (SARDI), Hart Field Site Group, Moodie Agronomy, Birchip Cropping Group, Agriculture Victoria, FAR Australia, Mallee Sustainable Farming. Collaboration with New South Wales DPI and Central West Farming systems.

Contact details

Kenton Porker
kenton.porker@sa.gov.au