Pros and cons of longer season varieties in Central West cropping environments

Author: Neil Fettell (1), James Hunt (2)(3), Bonnie Flohr (3), Barry Haskins (4), Rachael Whitworth (4) | Date: 28 Feb 2017

1Central West Farming Systems and University of New England, 2La Trobe University, 3CSIRO Agriculture, 4Ag Grow Agronomy & Research

Take home messages

  • Longer season wheat varieties have the potential to give greater yields than quicker varieties, particularly when sown into high levels of stored soil moisture
  • Effective fallow weed control and stubble retention increase the chances of successful early sowing
  • The combination of variety choice and sowing date is crucial in ensuring that crops flower in the preferred window.
  • Higher yielding varieties for early sowing are being developed.

Background

Longer season wheat varieties have been grown in central NSW over many years, but their area has declined in recent decades. The millennial drought, less frequent early autumn breaks and a succession of dry springs favouring quicker varieties have contributed to this change. Over the same period Australian wheat breeders focussed on cultivars with increasingly rapid development through selection of insensitive photoperiod and vernalisation alleles. There were few longer season varieties released, particularly mid-developing winter wheat cultivars (similar to EGA Wedgetail, Wylah, Whistler), following closure of the Temora breeding program in 2002.

A swing to mainly quicker varieties contracts the sowing window even as many growers are increasing their cropping programs, and there is evidence that April-May rainfall is declining. Late establishment can expose the crop to the increasing risk of drought and high temperatures in late spring. Summer and early autumn rainfall has not declined over the same period, and an opportunity exists to remove reliance on April-May rain for establishing crops by conserving soil water and using it to establish crops earlier than is commonly practiced.

A concern with early sown crops is that they might produce excessive dry matter and use stored water prior to flowering, resulting in poorer grain set and grain filling, leading to a low harvest index and poorer yield. However, in eastern areas, moisture from summer and early autumn rain is now routinely conserved via improved fallow weed control. In more western areas, long (18 month) fallow is an important component of farming systems. Long fallowing and early sowing are complementary practices, as the fallow reduces weeds and diseases which can be difficult to control in early sown crops, and early sowing with slow developing cultivars allows the crop to better use soil water that is stored at depth during the fallow. Stored soil water also helps to establish early sown crops when there is minimal autumn rainfall. Sowing machines with greater tine breakout pressures and presswheels are now common, as is stubble retention which preserves soil moisture closer to the soil surface. These changes improve the likelihood of good establishment with early sowing.  A shift in establishment date requires cultivars which are slower to develop so that they do not flower too early and risk damage by frost or reduced yields from insufficient dry matter accumulation.

The importance of flowering time

One of the main drivers of wheat yield and quality is flowering time. When selecting a cultivar and sowing time combination, the intention is to match plant development with seasonal pattern and most importantly get the crop to flower during the optimal period for yield. In central NSW the optimal flowering period varies from late August in the west to early October in the east (Table 1). This period is a trade-off between increasing drought and heat, and declining frost risk. There is no ‘perfect’ time to flower where these risks are nil, only an optimal period where they are minimised and yield on the balance of probabilities is maximised.

Table 1: Optimal flowering periods, peak of the mean of frost-heat adjusted APSIM yield and corresponding flowering date and sowing date range for a mid-fast cultivar for 51 years (1963-2013) for locations in NSW (from Flohr BM, Hunt JR, Kirkegaard JA, Evans JR 2017 Drought, radiation, frost and heat define the optimal flowering period for wheat in south-eastern Australia. Submitted).

Optimal flowering
period

Peak mean yield
(t/ha) and corresponding
 flowering date

Median sowing date for
corresponding
peak mean yield
(mid-fast cultivar e.g. Suntop)

Location

Open

Close

Nyngan

26-Aug

29-Aug

2.23

27-Aug

2-May

Merriwagga

27-Aug

10-Sep

2.62

31-Aug

27-Apr

Condobolin

11-Sep

19-Sep

2.43

15-Sep

7-May

Dubbo

15-Sep

22-Sep

3.88

18-Sep

11 May

Bogan Gate

18-Sep

1-Oct

3.65

21-Sep

13-May

Temora

25-Sep

10-Oct

3.04

3-Oct

13-May

From Table 1 it is evident that in most locations the preferred sowing date for peak mean yield of a mid-fast variety occurs in May. Slower developing varieties are needed for earlier sowing and breeders can achieve this in several ways. One is by increasing photoperiod sensitivity, which results in flowering being delayed by short days. Another is by introducing a vernalisation response, so that a period of low temperature (e.g. <10oC ) is required before the plant will switch from producing leaves to forming a spike. The strongest requirement for vernalisation is in ‘winter’ wheat varieties.

In the presence of ample stored soil water, winter and slow developing spring cultivars sown early often yield more than faster cultivars sown later (Tables 2 & 3). This is because the longer growing season available to early sown crops allows them to grow deeper roots and extract more water, reduce soil evaporation and produce more biomass. They may also tolerate winter water-logging better. However, if there is no stored soil water for growth around anthesis and grain filling, early sown crops can hay off and will yield the same or in some cases less than faster developing cultivars sown later. Lower seeding rates and delayed nitrogen application can be used to mitigate this risk.

An example of this is shown in Table 4. At Condobolin in 2011, dry conditions in late winter reduced grain set in the earliest sowings and similar yields were obtained from sowing dates ranging from 15 April until 16 May. The higher biomass from sowing earlier was offset by a lower harvest index, even at a low plant density. Whilst there was an increase in harvest index and yield at low plant densities for slow maturing varieties sown early (EGA Eaglehawk, Bolac), there was a yield penalty at low plant densities for fast maturing varieties sown later (Lincoln , Axe).

Table 2. Grain yield for a range of cultivars of different development rates sown on two dates on long fallow at Rankins Springs in 2015.

Grain yield (t/ha)

Cultivar

Development speed

15-Apr

14-May

Wedgetail

Winter

6.2

4.9

Kiora

Slow spring

6.1

5.1

Wylah

Winter

6.0

5.0

Bolac

Slow spring

5.9

4.3

Lancer

Slow spring

5.8

4.9

Gregory

Mid spring

5.3

4.0

Sunvale

Slow spring

5.3

4.8

Eaglehawk

Very slow spring

5.1

4.5

Condo

Fast spring

3.0

4.7

P-value

<0.001

LSD (p=0.05)

0.5

Table 3. Grain yield (t/ha) and stem frost damage (% tillers frosted) for a range of cultivars of different development rates sown on two dates on long fallow at Rankins Springs in 2014. This trial suffered severe damage from stem frosts in July and August which reduced yield in slow developing spring cultivars sown early.

Grain yield (t/ha)

Stem frost damage
(% sterile tillers)

Variety

17 April

22 May

17 April

22 May

Wedgetail

5.8

4.6

1

0

Osprey

5.3

4.8

1

-1

Lancer

4.5

4.5

27

0

Eaglehawk

4.4

4.4

8

1

Sunvale

4.2

4.7

44

-1

Suntop

4.0

4.4

18

0

Gregory

4.0

4.9

29

0

Bolac

3.8

4.6

30

0

Dart

3.5

3.9

43

0

Spitfire

3.4

4.1

42

0

P-value

<0.001

 <0.001

LSD (P=0.005)

0.4

7

Winter cultivars (e.g. Wedgetail) have the greatest range of potential establishment dates, but have been of more value to mixed farmers who can graze these crops in the vegetative phase (typically for ~1000 DSE/ha grazing days). Because they take longer to reach stem elongation, winter cultivars are also less susceptible to stem frost than slow spring cultivars (Table 3). There is unlikely to be a yield advantage of sowing winter cultivars intended only for grain production before early April as the extra vegetative biomass production will not contribute to grain yield.

Table 4. Grain yield and harvest index of five wheat varieties of different maturity sown at two plant densities at Condobolin in 2011 to flower on the same date.

Grain yield (t/ha)

Harvest index

Variety & sow date

30 plants/m²

90 plants/m²

30 plants/m²

90 plants/m²

EGA Eaglehawk (15 April)

3.4

3.1

0.37

0.32

Bolac (27 April)

3.3

2.9

0.38

0.35

EGA Gregory (5 May)

3.6

3.2

0.44

0.39

Lincoln (16 May)

2.8

3.0

0.46

0.45

Axe (25 May)

2.1

2.6

0.45

0.44

P-value

0.029

0.027

LSD (P=0.05)

0.4

0.02

Australian wheat breeders have increased their emphasis on varieties for earlier sowing in recent years. Slower spring varieties have been released (e.g. Lancer, Kiora, Flanker, Sunlamb, Suntime) as has a new winter variety (Kittyhawk). Winter cultivars will be more attractive as cultivars better adapted to western NSW become available. Wedgetail can be too slow to develop in this region even when sown early; varieties with a lower vernalisation requirement or faster development once vernalised should perform better. An example of the yield potential of the lines being developed can be seen from trials at Temora in 2015 and 2016 (Table 5). A faster winter line, RAC2341, was outstanding from a 17thApril sowing in 2015 and also performed well in 2016. There were few significant differences among the range of commercial varieties sown at their recommended times.

Table 5. Grain yield of seven wheat varieties of different maturity sown at their recommended times at Temora in 2015 and 2016. 

Variety & sowing date

Development speed

Grain yield (t/ha)

2015, 2016

2015

2016

Wedgetail  - 17, 14 April

Mid winter

4.3

6.5

Eaglehawk - 17, 14 April

Very slow spring

4.3

6.2

RAC2341 - 17 April

Fast winter

5.5

6.5

Lancer - 27 April

Slow spring

4.8

Bolac - 26 April

Slow spring

6.5

Gregory - 7, 6 May

Mid spring

3.9

6.2

Condo - 15, 15 May

Fast spring

4.4

6.8

P-value

<0.001

<0.001

LSD (p=0.05)

0.4

0.8

Conclusions

Longer season wheat varieties, of both winter and slow spring growth habit, have a valuable place in modern farming systems in the Central West. Combined with effective fallow water storage, they have the ability to out-yield later sowings. By extending the sowing window, they can contribute to timeliness of the whole sowing program and improve average farm yields.

Acknowledgements

The research undertaken as part of this project was made possible by the significant contributions of growers through the GRDC. We gratefully acknowledge the guidance of local farmers in this work, particularly Michael Pfitzner who hosted the Rankins Springs trials in 2014 and 2015, and the input of the CWFS, CSIRO and Ag Grow Agronomy trial staff. 

Contact details

Neil Fettell
‘Myuna’ Condobolin NSW 2877
Ph: 02 6896 5342
Mb: 0427 201 939
Email: neil.fettell@une.edu.au

Varieties displaying this symbol beside them are protected under the Plant Breeders Rights Act 1994.

GRDC Project code: CSP00178