Frost Learning Centre (FLC) for growers, advisers and researchers

Take home messages:

• Zoning farms and paddocks based on frost risk (red, amber and green zones) is the starting point for frost management.
• Planning prior to seeding improves the ability to mitigate frost risk. Tools to mitigate risk include varietal selection and mixtures, dual purpose cereals, attending to previous crop residues, or selecting crop/enterprise types that are either more tolerant to or able to avoid frost.
• The relationship between canopy size and grain yield in the presence of frost remains unclear, although the financial risk associated with crop inputs and frost needs to be evaluated closely.

Background

The South Australian Grain Industry Trust’s (SAGIT) project, with GRDC co-investment, of the Frost Learning Centre (FLC) is the culmination of many years of frost research conducted in Mid North SA by Agrilink Agricultural Consultants. The FLC is a cereal focused trial with the site located in a paddock with an area at high risk of frequent and severe frosts (red zone) and an area relatively unaffected by frost (green zone). This enables comparison, with and without frost, for certain trials where it is considered important. Trials are focused on a range of frost intervention, prevention, and mitigation strategies to give growers and advisers options with frost management.

The Western Australian Department of Primary Industries and Regional Development (DPIRD), notably Dr Amanuel Bekuma, Dr Brendan Leske and Dr Ben Biddulph, have increased the understanding of the role of ice nucleating bacteria in plant freezing and frost damage. The FLC has increased the focus on the local impact and understanding of ice nucleating bacteria as the project has progressed.

Method

The key objectives of the FLC are to conduct applied research and extension into aspects of frost including avoidance, tolerance, mitigation, identification, and strategies to reduce yield, financial loss and stress from frost. This is complemented by investigation, creation and extension of new methodologies and the evaluation of existing and new technologies. Technology evaluation includes, but is not limited to, frost exclusion shelters, infra-red thermography, and remote sensing. The FLC has more recently focused on the role of ice nucleating bacteria, interactions of plant protection products and adjuvants and the investigation of frost mitigation and prevention products. Lastly, the FLC aims to provide a forum for growers and advisers to learn and discuss and as a collaboration site for other research endeavours.

Results and discussion

Zoning

The zone method for identifying frost risk enables growers and advisers to create and implement long term strategies and short term tactics in zones as defined below:

• RED ZONE: Where frost and related damage is either severe, frequent, or both. The financial impact is substantial.
• AMBER ZONE: Sometimes frosted, sometimes not, depending on the severity of the frost. In any frost that occurs, the amber zone can experience losses in a range from none to severe. Damage in the amber zone graduates in intensity from the green to the red zone.
• GREEN ZONE: Frost is not an issue – aim to maximise returns.

Zoning allows strategies and tactics to be tailored based on frost risk. Strategies to manage frost almost always result in reduced financial returns when compared to the optimum green zone management strategies, hence the importance to only use them where frost is an issue. Zoning can be completed using knowledge of the landscape and paddock with relevant elevation, soil type, topography and yield maps assisting with identification.

The challenges of frost research

Replicating frost research results across seasons is a difficult task. The varied timing, severity, time of seeding (dry starts), very late season rain and absence of damaging frost events in 2022 has contributed to the challenge of drawing meaningful insights from the project data. The 2021 season had a dry start, with the opening rain not occurring until 25 May. An even later start occurred in 2022, with opening rains falling on 30–31 May. The 2023 season had a mid-April break, but germination of the trials didn’t occur until follow-up rain on 20–21 May and 30 May. Table 1 shows the TOS 1 grain yields of a range of varieties grown across all three years of the FLC. Germination occurred from the 20 May to 1 June for all varieties across all three years in table one. The variability is driven by unpredictable timing of frost events, crop growth stage at the time of the event(s) and number and severity of individual frosts.

Table 1: Grain yield (kg/ha) of cereal varieties at an early time of sowing (TOS1) (germination late may -early June) across the three years of the FLC. Each season has been analysed separately with letters denoting significance at the p<0.05 statistical confidence level. GRDC Crop sowing guide 2024 variety maturity classes been listed on the table.

Temperatures quoted in this paragraph are recorded at 1.25m above ground level in a Stevenson screen. There is not a linear relationship between frost induced crop damage and the temperature measured either within the Stevenson screen or the ambient air temperature at canopy height during the critical period. The timing and frequency of major spring frost events varied between seasons:

• In 2021, there were 17 nights during spring where the temperature was at or below 0°C. There were two major frost events on 11October and 28 October where the minimum temperature reached -3.6°C and -2.8°C respectively, with time below 0°C being longer than seven hours on both nights. Late rains in early November, after these severe frost events, is suspected to have aided plant recovery in some trials/varieties.
• In 2022, there were six nights below 0°C in spring, with the coldest temperature being -2.56°C on 3September and -2.5°C on 10 October, with both nights being below 0°C for at least seven hours. The barley cultivars were at head emergence and earliest wheat varieties were at the booting growth stage. There was limited damage observed. After the 10 October event, there were no further significant frost events and high grain yields resulted (table one).
• In 2023, there were eight nights during spring where minimum temperatures was below 0°C, with the coldest being the morning of 26 October, with a minimum of -5.5°C, with nine and a half hours below zero. Early maturing varieties in TOS 1 were sufficiently advanced (approximately soft dough Zadoks GS 85 and later) that severe grain yield loss didn’t occur, although visibly frost affected grain was seen in some quick and quick-mid maturity varieties. There was major damage in the slow maturity varieties in TOS 1 and all varieties in TOS 2.

Phenology

Figure 1. Phenological development of wheat, barley and oat varieties sown in the red zone on 17 April 2023 (TOS1), showing Zadoks GS 39 at the base of the bar and GS71 at the top of the bar with GS 65 highlighted.

An understanding of phenology enables growers and advisers to make variety selections for their environment to target flowering during a period where abiotic factors (low radiation, frost damage, high temperatures, heat shock and water stress) are minimised. It is a strategy that weighs up the risk of these opposing factors and attempts to avoid the major frost window. The avoidance strategy can work for specific locations where there is greater degree of confidence that the dates of the last frost can be reasonably well predicted i.e where frost occurs at lower altitudes. The timing of frost differed between the years with early sown, fast maturity varieties in 2023 avoiding frost events and outyielding early sown, slow maturing varieties.

The three drivers for phenological development are temperature, photoperiod and vernalisation. Varieties that have vernalisation and photoperiod requirements feature strongly in the later flowering end of Figure one and two. While barley has a reputed higher tolerance to frost, all varieties, except the winter barley NewtonA, have early maturities that generally increase exposure to more frost events in winter and early spring. This may not normally be considered part of the frost window and exposure to this period is increased if the quick barley varieties are sown too early.

Figure 2. Phenological development of wheat, barley and oat varieties sown in the red zone on 17 May 2023 (TOS2), showing Zadoks GS 39 at the base of the bar and GS71 at the top of the bar with GS 65 highlighted.

Nitrogen and canopy

The nitrogen and canopy trial investigated the impact of canopy size and nitrogen rate on frost damage, with the canopy size being altered using seeding rate and nitrogen rate. This trial has been repeated for all three years of the FLC, with the same seeding rate treatments of CalibreA wheat and nitrogen rates applied. Canopy variation was produced by using seeding rates of 80 seeds/m2 and 300 seeds/m2 and manipulated with nitrogen rates of 0, 25, 50, 100, 200, 400kgN/ha. Timing of nitrogen application was during the vegetative growth period with the aim to produce a range of canopy sizes and not to assess frost damage response to timing of application.

Table 2: Impact of nitrogen (N) application and seed rate on grain yield and net returns of Calibre* wheat. Results are recorded over three years of the FLC with statistical significance noted at the (P<0.05) confidence level. Statistical analysis was completed within a season across all seeding rate and nitrogen treatments. GY = Grain Yield, NR = Net Revenue after nitrogen expense. Assumptions used: Grain price $350/t and Nitrogen price $1378/t.

There were no clear trends observed across the three seasons. All three years of this trial were sown into faba bean stubbles, with starting soil nitrogen levels, sampled from 0- 120cm depth, of 46kgN/hain 2021, 121kgN/ha in 2022 and 52kgN/ha in 2023. In 2021, there was a significant yield response to the high seeding rate and high nitrogen rate treatments. Late season rains in 2021 are suspected to have aided recovery from frost in high nitrogen treatments due to later order tillers producing substantial grain. In the 2022 trial, there was negligible frost impact on the trial, and high starting soil nitrogen resulted in a low yield response to applied nitrogen. In 2023, there was extremely severe frost and no clear trends in the data due to the severity of the effects across all treatments.

The financial risk associated with applying nitrogen is critical to consider in red zones. While high nitrogen rates produced the highest yields in 2021 and 2022, generally net returns either didn’t increase as nitrogen rates increased and, at some rates, decreased. In 2023, a similar outcome was produced, except that returns were much lower due to the severe frost damage. This indicates variability of return and high level of financial risk that is associated with applying nitrogen in a frost-prone area. In these areas, an appropriate strategy may be to soil test to evaluate nitrogen levels, apply a rate at the low end of the appropriate rate range to reduce the amount of financial loss in the event of a frost, while not severely limiting returns in the absence of severe frost. This approach to red zones could be balanced with a more aggressive nitrogen strategy in green zones. If a salvage hay cut operation is available, then growing acceptable dual-purpose cereals and applying nitrogen earlier in the season can maximise dry matter production. In the event of frost, there may be a profitable return by cutting for hay, albeit this strategy is not without risk.

Additional research activities

Additional research activities conducted at the FLC in 2023 included:

• delay and reset of cereal phenology including a PGR assessment
• impact of crop residue on frost outcomes
• wheat and barley varietal mixtures
• impact of use of frosted seed, variety and time of seeding on frost outcomes
• impact of PGR use on wheat and barley frost outcomes
• impact of use of frost protection products on frost outcomes
• dual purpose cereals
• assessment of biological agents on frost outcomes
• limited assessment of herbicide and adjuvant application on frost outcomes.

Conclusion

Frost mitigation begins with knowing the areas on farm that are impacted by frost and delineating zoning based on the frequency and severity of the frost. This enables appropriate strategies to be implemented to mitigate frost risk and the associated financial implications, but risk cannot be eliminated completely, as seen with 2023 FLC results. Minimising financial exposure to frost events is critical for business sustainability, so having an alternative crop use, managing nitrogen expenditure and being cautious of investing in products promising improved frost outcomes may help to minimise this risk.

Acknowledgements

The support of South Australian Grain Industry Trust (SAGIT) and additional financial support from GRDC is acknowledged for this project. The dual-purpose cereal research is supported by Agrifutures and Balco Australia.

The authors would like to thank frost-affected growers for their valuable support, particularly the businesses that provided suitable trial sites. We would also like to acknowledge the involvement of SARDI for co-locating innovative pulse research, the MNHRZ committee for the organisation of many field days and workshops, suppliers of the products used in the trials and Dr Philip Brewer for his assistance with plant growth regulator selection. Lastly, we would like to acknowledge the support of DPIRD, especially Dr Amanuel Bekuma, Dr Brendan Leske and Dr Ben Biddulph for the laboratory testing of ice nucleating bacteria activity.

Useful resources

Frost management 

Contact details

Ben Smith
Agrilink Agricultural Consultants
7813 Horrocks Highway, Penwortham SA 5416
0429 202 725
ben.smith@agrilinkag.com.au
@bensmith213

Mick Faulkner
Agrilink Agricultural Consultants
7813 Horrocks Highway, Penwortham SA 5416
0428 857 378
mick.faulkner@bigpond.com
@MidNorthHRZ