Wheat sowing time: finding an adaptable variety

By BCG Staff and Contributors
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With decreasing autumn rainfall, ‘late’ breaks are becoming a characteristic of Wimmera and Mallee cropping systems. This presents growers with a conundrum: to sow to the calendar or sow following a substantial breaking rain and into a moist seed bed? As farm sizes continue to increase, it is difficult to complete the full sowing program at the desired time, in ideal conditions. Therefore, it is important to identify varieties that are adaptable to a range of sowing and emergence dates.

While sowing into a moist seedbed can be advantageous for crop emergence and weed control, delaying sowing to achieve this comes with considerable risk of heat shock and dry finishes. However, sowing early presents an increased risk of yield penalties caused by frost (Gomez-Macpherson and Richards 1995).

In order to maximise yield, it is important to understand how different varieties and phenology groups behave when sown at different times (Hochman et al. 2012).

TAKE HOME MESSAGES

  • Sowing in May rather than June consistently results in yield benefits.
  • Growing a variety that is adaptable to sowing dates, such as Mace or Corack, reduces the yield penalty from later sowing and late breaks.
  • Sowing different varieties with a range of maturity groups/sowing dates is important in managing risk.

AIM

To ascertain the performance of a range of wheat varieties at different sowing times, over three different seasons.

TRIAL DETAILS

Location: Horsham
Soil type: Heavy clay, with subsoil constraints
Annual rainfall: 2015 – 228mm, 2014 – 226mm, 2013 – 404mm
GSR (Apr-Oct): 2015 – 125mm, 2014 – 172mm, 2013 – 341mm
Crop types: Refer to Table 1.
Sowing dates:
2015 – 18 May and 22 June
2014 – 9 May and 9 June
2013 – 5 May and 18 June
Seeding equipment: Knife points, press wheels, 30cm row spacing
Target plant density: 2015 and 2014 – 150 plants/m², 2013 – 130 plants/m²
All trial inputs (fertiliser, pesticides and fungicides) were managed in order to maximise yield.

METHOD

Replicated field trials were established in the same paddock at Horsham for the 2013, 2014 and 2015 cropping seasons. The trials were conducted using a randomised complete block design, comprising four replicates.

The treatments consisted of a desired sowing date, in early-mid May and a later sowing date, approximately a month later. A range of varieties were selected to represent varieties commonly grown in the region, as well as a range of maturity types (Table 1).

Wheat TOS Table 1

Grain yield and quality were analysed to determine any potential penalty from sowing later than the desired time. Yield and quality data were statistically analysed using a two-way analysis of variance.

RESULTS AND INTERPRETATION

Sowing in May consistently resulted in significantly higher yields than sowing later (Table 2). The greatest impact of a later sowing time was seen in 2015, with an average yield penalty of 41 per cent. This wide discrepancy can be attributed to below average spring rainfall (Table 3) and above average spring temperatures (data not presented). This allowed the crops sown in May to fully utilise the short growing season, while the later treatment began to flower and ripen when the conditions became increasingly warmer and drier (Gomez-Macpherson and Richards 1995).

 

Wheat TOS Table 2

Wheat TOS Table 3

A similar trend was seen in 2014. However, a number of frosts occurred during the flowering period of the May sown treatment, which prevented these crops from reaching their potential. Nevertheless, the dry spring was more significant than the frost, hence the lower yields in the June sown treatment.

Conversely, though 2013 experienced above average spring rainfall, a similar trend was experienced (although not to the same extent). While grain yield was significantly affected by the different sowing times, grain quality attributes were not significantly different between sowing dates (data not presented).

Overall, sowing in May produced the highest yields, but not all varieties performed similarly when sown at the different times. Crop performances proved to be largely dependent on the environmental conditions of the growing season, as well as on the phenology of the individual varieties.

The aforementioned spring conditions experienced in 2015 significantly decreased the yields of all varieties when sown late. The later maturing varieties such as Scout and Trojan displayed the greatest reduction in grain yield, while earlier maturing varieties such as Mace, Corack and Cosmick were able to utilise a shorter growing season more efficiently, therefore the yield penalties were not as great (Table 4).

Wheat TOS Table 4

The 2014 season was unique due to the numerous frosts which occurred in spring, coupled with the below average rainfall throughout this period. In terms of sowing timing, a similar trend to 2015 was observed, but it was not as significant. In the later sown treatments in 2014, the yields of later maturing varieties were limited by the warm, dry conditions, while the yields of earlier maturing varieties were limited by frost events, resulting in all varieties performing similarly.

In 2013, above average rainfall was received, which provided an opportunity to observe variety performance in a higher yielding year. The impact of later sowing on slower maturing varieties such as Scout and Trojan was not as substantial as seen in the subsequent two years. However, these varieties still yielded significantly higher when sown earlier rather than later.

COMMERCIAL PRACTICE

These results confirm that, regardless of autumn rainfall, sowing wheat earlier rather than later will maximise the achievable yield. Naturally, this presents a logistical challenge, however this can be viewed as an opportunity to manage risk by including a mix of varieties within the rotation. For instance, sowing a proportion of later maturing varieties such as Scout or Trojan early, followed by quicker maturing varieties such as Mace, Cosmick or Corack will help to manage the yield risk presented by frost and heat stress.

Moreover, sowing a variety that will perform at a range of sowing and emergence dates will relieve pressure on logistics and planning. Mace and Corack have proven to be adaptable varieties that will yield well regardless of sowing date or season, although growing these varieties will present other agronomic challenges such as disease management, which should also be considered in variety choice (Table 5) (Lawes et al. 2015).

Wheat TOS Table 5

ON-FARM PROFITABILITY

Sowing in June rather than May has consistently resulted in yield reductions and ultimately lost income. In the 2013 and 2014 seasons, the later sowing time resulted in an average $114/ha of lost income, while in the 2015 season a later sowing date incurred a $200/ha income penalty (based on a grain price of $285/t). Sowing an adaptable variety such as Mace as opposed to Scout has resulted in an average $57/ha increased income over the past three seasons, regardless of sowing date. This does not take into account any inputs, for instance fungicides, which may represent a higher cost for Mace than for Scout. However, in lower rainfall years, where these additional inputs have not been necessary, Mace has significantly outperformed Scout over a range of sowing dates.

REFERENCES

Department of Economic Development, Jobs, Transport and Resources (2015) Victorian winter crop summary, Available at https://www.nvtonline.com.au/wp-content/uploads/2015/02/NVT-Victoria-WinterCrop-Summary-2015_Screen1.pdf. (Verified 12 January 2016).
Gomez-Macpherson H, Richards RA (1995) Effect of sowing time on yield and agronomic characteristics of wheat in south-eastern Australia. Australian Journal of Agricultural Research 46 , 1381–1399.
Hochman Z, Gobbett D, Holzworth D, McClelland T, van Rees H, Marinoni O, Navarro Garcia J, Horan H (2012) Quantifying yield gaps in rainfed cropping systems: A case study of wheat in Australia. Field Crops Research, 136, 85-96.
Lawes R, Hochman Z, Huth N (2015) Commercial wheat varieties are broadly adapted to time of sowing in Australia. In ‘Building Productive, Diverse and Sustainable Landscapes Proceedings of the 17thAustralian Agronomy Conference 2015’. (Eds T Acuña, C Moeller, D Parsons, M Harrison) pp.1-4. (Australian Society of Agronomy Inc.: Warragul, Vic).

ACKNOWLEDGEMENTS

This research was funded by BCG members through their membership, in conjunction with Agritech Rural, Horsham.

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