Sorghum and maize – avoiding yield loss to heat at grain fill through agronomy and changing the sowing window

Call to action/take home messages

Sorghum

  • Sorghum emerged in 2017 at cold soil temperatures (~ 8°C at Breeza) but establishment percentages were low. The first time of sowing (TOS1) was 57% of the established population of the third time of sowing (TOS3).
  • Plants were still emerging 47 days post sowing of the very early sowing time (TOS1).
  • The very early and early sowing times (TOS 1 and 2) resulted in patchy, uneven plant stands which were more prone to weed competition.
  • The very early and early sowing times did not achieve the target plant population of 50,000 plants/ha.
  • Sowing deeper (~7-8 cm) resulted in higher establishment losses compared to the shallow sowing.
  • There were differences in the establishment between hybrids, however these were often not consistent across sites and times of sowing.
  • High quality seed; germination and vigour; is required to achieve the best results - especially under colder soil temperatures.

Maize

  • Maize establishment in 2017 was delayed at TOS 1 and 2 by sowing into cold soil temperatures
    (~ 8°C and ~10°C at the Breeza site) but final plant populations were comparable to sowing into warmer soil temperatures.
  • There was no difference in the establishment of the three hybrids in this experiment.

Introduction

Recent summer seasons have exposed dryland sorghum and maize crops in northern NSW to extreme climatic events of heat and moisture stress resulting in reduced grain yields, sometimes total crop failure and poor grain quality.

As a result, alternatives to the conventional sorghum and maize production systems are being sought. There is a need to move the critical stages of flowering and grain fill away from the late December/early January timeframe to avoid the high likelihood of extreme temperatures in this period.

In order to minimise the impact of these heat stress events, several tactics which growers could readily adopt into their current farming systems were evaluated in these experiments.

They were:

  • To sow earlier, into soil temperatures lower than the current commercial recommendations of 16-18°C for sorghum and 12°C for maize.
  • Develop new information on the tolerance of hybrids to cold sowing to assist in early sowing.
  • Sow deeper into warmer, more stable soil temperatures.

Research methods

2017/18 season, experiments were sown in three dryland locations in northern NSW using a Monosem precision planter.

Establishment counts were conducted 5 - 7 days after sowing and then at weekly intervals until plant emergence had ceased. Days to flowering and plant cuts were taken at physiological maturity to provide biomass and harvest index information.

At the time of writing, the experiments had not yet reached harvest. However, all experimental sites will be harvested and grain yield and grain quality parameters measured.

Sorghum experiments

In the 2017/18 season three sorghum dryland experiment locations were conducted:

Region

Location

Time of sowing (TOS) and date

Row spacing

TOS 1

TOS 2

TOS 3

Liverpool Plains

Liverpool Plains Field Station

10th August

28th August

21st September

1.0 m solid

Moree East

Gurley

2nd August

21st August

17th October

1.0 m solid

Moree West

Mallawa

1st August

24th August

18th Oct

1.5 m solid

The experiments included three factors:

  1. Time of sowing
    The time of sowing was determined based on target soil temperatures to capture very early sowing, early sowing and commercial standard. The soil temperature data used was measured at 8am Eastern Daylight Saving Time (EDST) at depths of 3 and 7 cm. Soil temperature loggers were used at each site. The targeted soil temperatures were:
    1. Very early - 10°C
    2. Early - 14°C
    3. Conventional - 16-18°C
    4. Seeding depth
  2. Seeding depth
    Two seeding depths were included to evaluate if sowing deeper would provide warmer, more stable soil temperatures to improve crop establishment.
    1. Shallow – 4 cm
    2. Deep – 7-8 cm
  3. Hybrid selection
    1. 9 hybrids: MR Buster, MR Apollo, 85G33, Cracka, Tiger, Agitator, Archer, HGS102, HGS114.

The sorghum experiments were sown targeting a plant population of 50,000 plants/ha.

Maize experiments

Three maize experiments were conducted in the 2017/18 season and included three factors:

Region

Location

Time of sowing (TOS) and date

Row spacing

TOS 1

TOS 2

TOS 3

Liverpool Plains

Liverpool Plains field station

9th August

29th August

20th September

1.0 m solid

Moree East

Gurley

31st July

22nd August

17th October

1.0 m solid

Moree West

Mallawa

1st August

24th August

18th October

1.5 m solid

  1. Time of sowing
    The time of sowing (TOS) was based around target soil temperatures to simulate early sowing, commercial standard and late sowing. Soil temperature loggers were used at each site.
    1. Early - 10°C
    2. Conventional - 14°C
    3. Late - 16-18°C
  2. Plant population – four target plant populations
    1. 15,000 plants/ha
    2. 30,000 plants/ha
    3. 45,000 plants/ha (Mallawa and Gurley only)
    4. 60,000 plants/ha
    5. 120,000 plants/ha (Breeza only)
  3. Hybrid selection
    Three hybrids were selected as examples of certain plant types. These plant types were either prolific (producing tillers with cobs), non-prolific multi cobbing (no tillers but potential for more than one cob on the main stem), non-prolific single cob with flex (where yield compensation is usually gained through a longer cob). Medium maturity hybrids were selected with a similar maturity or Corn Relative Maturity CRM.

The three hybrids used in these experiments were selected based on their differing plant types:

Hybrid

Plant type

CRM

End Use

Pioneer - 1467

Prolific - tillers with cobs

114

Silage and grain

Pioneer - 1756

Main stem, multiple cob

117

Processing (grit, feed, silage)

Pacific Seeds - 606IT

Main stem, single cob

114

Silage/ grain

Results

Sorghum

Time of sowing

Sorghum establishment was very slow for both TOS 1 and 2. There were no plants emerged until 30 days after sowing (DAS) for TOS 1 and 23 DAS for TOS 2. At the last establishment count, 47 DAS, the established plant population for TOS 1 was only 57% that of TOS 3. The targeted plant population of 5 plants/m2 or 50,000 plants/ha was achieved by 23 DAS for TOS 3 only (Table 1).

Table 1. Sorghum plant establishment (plants/m2) at Breeza research station (averaged across hybrids)

TOS

Days after sowing (DAS)

5

14

23

30

37

42

47

1

0.0

0.0

0.0

0.2

 

2.2

2.8

2

0.0

0.0

1.6

2.7

3.3

3.4

 

3

0.0

4.2

5.4

4.9

   

Sowing depth

There was a difference in soil temperature between the deep and shallow depths. On average across all sites, it was 0.6°C warmer at the deeper sowing depth.

At all three sites the plant establishment was better from the shallow sowing depth of 4-5 cm, compared to the deep sowing depth of 7-8 cm. This result was consistent across each of the sowing times, demonstrating that even under warm soil temperatures, there was still a reduction in establishment as a result of the deeper sowing depth. Seedbed moisture also needs to be considered as the soil dries out faster at the shallow depth. At the Breeza site only, an irrigation flush was applied prior to sowing to ensure even seed bed moisture. The temperatures at Breeza were lower compared to the other two sites.

Figure 1 is a line graph which shows soil temperatures at Breeza in 2017 (sowing dates - TOS 1, TOS 2 and TOS 3 - indicated by arrows)

Figure 1. Soil temperatures at Breeza in 2017 (sowing dates indicated by arrows)

There was no statistical difference in the time taken to emerge based on the weekly assessments. The results from the Breeza site only are contained in Table 2.

Table 2. Impact of sowing depth on sorghum establishment (plants/m2) at Breeza research station

Days after sowing

TOS

Seed depth

5

14

23

30

37

42

47

1

Shallow

0.0

0.0

0.0

0.2

-

2.5

3.0

Deep

0.0

0.0

0.0

0.3

-

1.8

2.6

2

Shallow

0.0

0.0

2.3

2.8

3.7

3.8

-

Deep

0.0

0.0

0.8

2.6

2.8

3.0

-

3

Shallow

0.0

4.5

5.6

4.8

-

-

-

Deep

0.0

3.9

5.2

5.0

-

-

-

Hybrid selection

The nine sorghum hybrids used in these experiments established differently. The results were not always consistent across all three sites. The data from Breeza has been shown below (Figure 2) for a selection of four hybrids. Two hybrids, MR Buster and MR Apollo, from Pacific Seeds showed no variation between each other. In contrast, the two hybrids from Nuseed, Cracka and Tiger, behaved differently at the two colder sowing times, TOS 1 and TOS 2. Cracka established more plants and quicker than Tiger.

These are preliminary observations from this site which need to be considered in the context of seed quality e.g. germination and vigour differences could explain some or all of this variation. As such a pot trial is being conducted in unison with these field experiments to gather more detailed information on temperature, emergence and the influence of seed quality.

Figure 2a is a scatter graph which shows plant establishment of varying sorghum hybrids at Breeza - MR Apollo and MR Buster

Figure 2 is a scatter graph showing plant establishment of varying sorghum hybrids at Breeza - Cracka and Tiger

Figure 2. Plant establishment of varying sorghum hybrids at Breeza

Maize

Time of sowing

There were no plants emerged until 7 DAS from each of the three sowing times. TOS 3 emerged rapidly between 7 and 14 days post sowing to reach the target plant populations, with the exception of the highest population. There was a significant delay in plant establishment for TOS 1 and 2 until 24 DAS, at which point the established populations were not significantly different between the three times of sowing (Figure 3). Plants were still emerging at 30 DAS from TOS 1.

Figure 3a is a column graph which shows maize establishment at 14DAS

Figure 3b is a column graph which shows maize establishment at 24DAS

Figure 3c is a column graph which shows maize establishment at 30DAS

Figure 3. Maize establishment –clockwise from top left a) 14DAS, b) 24DAS, c) 30DAS

Hybrid selection

The three hybrids all established well within their target plant population categories. As such no major differences in hybrid populations were present by the last time of counting at 42 DAS.

Plant population

The final plant populations were higher than the targeted plant populations for the 15, 30 and 60,000 plants/ha populations. However, the 120,000 population was not achieved The final established population was 84,000 plants/ha averaged across treatments.

Discussion

At the time of writing, these 2017/18 season experiments had not yet been harvested so data relating to grain yield and quality was not available. This information will ultimately assist in the discussion of whether any of these tactics; hybrid selection or type, sowing depth, sowing time or plant population can assist growers to avoid the impact of heat at flowering and grain fill.

Sorghum

Grain sorghum was able to be established at much lower temperatures than is commercially recommended, however there are other issues to be considered before adopting this approach commercially.

  1. Delayed/slow establishment
    TOS 1 resulted in a much slower emergence than the industry standard of TOS 3. Plants were still emerging 7 weeks post sowing. The growth of plants in this first 4-6 weeks was substantially delayed by the cold conditions and some plant losses were seen. Overall, plants were observed to be small, pale coloured or purple and suffering from ill thrift.
  2. Reduced establishment percentages
    When comparing across the three times of sowing, it can be seen that final established populations for TOS 1 and 2 never reached the same levels as TOS 3. In essence this means a large wastage in terms of seed costs to a grower; seeds which were sown but never emerged.
  3. Lack of uniformity in plant stands
    Due to the slow and reduced establishment in TOS 1 and 2, the plant stands contained more gaps and irregular spacing compared to TOS 3. This led to additional opportunities for weeds to emerge in these gaps and makes crop management decisions more difficult if the plant maturity is staggered.
  4. Weed control
    The slow and patchy emergence which resulted from TOS 1 and 2 meant an opportunity for weeds to emerge in the gaps. While pre and post emergent herbicide options were incorporated in these experiments, weeds still needed to be controlled by chipping in the experimental plots to remove any confounding effects of weed competition.

Maize

The effects of the colder sowing were much less evident in maize than in sorghum. Based on current agronomic recommendations for a colder soil temperature for maize compared to sorghum, this result is not surprising.

Hybrid selection

The three hybrids were selected based on varying plant types. These three plant types are being used as indicators of the potential for maize to be manipulated to improve reliability and yield, particularly in the less favourable maize growing environments such as west of Moree.

The synchronisation of tassels and silks is critical to ensure seed set. Moisture stress and heat at flowering are two of the most important influences on these plant processes.

There are several different theories relating to plant types:

  1. Plants with tillers allow more flexibility to respond to changing climatic conditions as the flowering time is spread over a longer period. Hence if poor seed set occurs on the primary stem cobs, then hopefully the tiller cobs can compensate.
  2. Tillers use valuable moisture and nutrients and never contribute significantly to grain yield.
  3. Plants with one cob only on the main stem have the greatest likelihood of producing the highest yield and quality (e.g. seed size)
  4. Plants with multi cobbing properties allow for more of the top end yield potential to be captured in favourable seasons.

Conclusion

The inclusion of final plant, grain yield and quality data from the three trial sites will add significant information to allow interpretation of the value of these treatments. It is important to consider that this data is only from one season so additional years data will add to the value of this dataset.

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 and NSW DPI, the author would like to thank them for their continued support.

Thanks to Paul Slack, “Koreen” Gurley and Jason & Geoff Hunt “Heathfield” Mallawa for hosting the experiments and Tony Lockrey with site assistance. The seed companies are thanked for allowing their hybrids to be used in the experiment.

Thanks to Delphi Ramsden, Simon Tydd and Alice Bowler for assistance with the data collection and management of the experiments. Thanks also to Scott Goodworth and Steve Gengos for assistance with the Breeza site.

Contact details

Loretta Serafin
NSW Department of Primary Industries
4 Marsden Park Road Calala NSW 2340
0427 311 819
Loretta.serafin@dpi.nsw.gov.au

GRDC Project code: DAN00195