Careful planning, zoning and choosing the right crops are the best options to reduce frost riskFrost damage to cereals is a significant annual production constraint for the Australian grains industry and can result in considerable yield losses. A comprehensive frost management strategy needs to be part of annual farm planning. It should include: pre-season, in-season and post-frost event management tactics.
- In some areas the risk of frost has increased due to widening of the frost event window and changes in grower practices.
- The risk, incidence and severity of frost varies between and within years as well as across landscapes, so growers need to assess their individual situation regularly.
- Frosts generally occur when nights are clear and calm and follow cold days. These conditions occur most often during winter and spring.
- The occurrence of frost and subsequent frost damage to grain crops is determined by a combination of factors including: temperature, humidity, wind, topography, soil type, texture and colour, crop species and variety, and how the crop is managed.
- Greatest losses in grain yield and quality are observed when frosts occur between the booting and grain ripening stages of growth.
- Frost damage is not always obvious and crops should be inspected within five to seven days after a suspected frost event.
- Methods to deal with the financial and personal impact of frost also need to be considered in a farm management plan.
Risk management for frostThe variability in the incidence and severity of frost means that growers need to adopt a number of strategies as part of their farm management plan. These include pre-season, in-season, and post-frost strategies.
Pre-season management tacticsThere are two types of pre-season management tactics available for growers: 1) at the level of farm management planning and 2) within identified frost zones of a farm.
Farm management planning tactics:
Step 1: Assess personal approach to riskConsider your personal approach to risk in your business; every individual will have a different approach. As part of this process identify and measure the extent of the risk, evaluate risk management alternatives and tailor the risk advice according to risk attitude. The risk of frost can often drive conservative farming practices, which should be carefully and regularly reviewed in light of the latest research.
Step 2: Assess frost risk of propertyCarefully consider the risk of your property incurring frosts due to the location. Use historic seasonal records and forecasts. Spatial variability (topography and soil type) across the landscape should also be considered as cold air will flow into lower regions. Temperature monitoring equipment, such as Tiny Tags, iButtons and weather stations can determine temperature variability across the landscape (see box Temperature tips).
Step 3: Diversify the businessA range of enterprise options should be considered as part of a farm management plan to spread financial risk in the event of frost damage. This is subject to the location of the business and skillset of the manager but the largest financial losses with frost have occurred where growers have a limited range of enterprises or crop types. Intensive cropping systems especially focused only on canola and spring wheat are often at the mercy of frost more than a diversified business as both crops are highly susceptible to frost damage.
Step 4: Zone property/paddockPaddocks or areas in paddocks that are prone to frost can be identified through past experience, the use of precision tools such as topographic, electromagnetic and yield maps and temperature monitors to locate susceptible zones. This can help determine the appropriate management practice to use to mitigate the incidence of frost. Be aware that frost-prone paddocks can be high yielding areas on a farm when frosts do not occur. Once the farm has been zoned as at risk of frost, the frost zone management tactics on page 3 can be considered.
Frost zone management tactics:
Step 1: Consider enterprise within a zoneThe use of identified frost zones should be carefully considered, for example using them for grazing, hay or oat production and avoiding large scale exposure to frost of highly susceptible crops like peas or expensive crops like canola. It may be prudent to sow annual or perennial pastures on areas that frost regularly in order to avoid the high costs of crop production.
Step 2: Review nutrient managementTargeting fertiliser (nitrogen, phosphorus, potassium) on high risk paddocks and seed rates to achieve realistic yield targets should minimise financial exposure, reduce frost damage and increase whole paddock profitability over time. These nutrients could be reallocated to lower risk areas of the farm. While high nitrogen (N) increases yield potential it will also promote vegetative biomass production and increase the susceptibility of the crop to frost. Using conservative N rates at seeding and avoiding late top-ups results in less crop damage. It is best if crops are not deficient in potassium or copper, as this may increase susceptibility to frost events. This can be assessed from initial soil tests and with plant tissue testing. Copper deficiency can be ameliorated with a foliar spray pre-flowering and as late as the booting stage to optimise yield, even in the absence of frost. Potassium plays a role in maintaining cell water content in plants, which can potentially influence tolerance to frost. It has been shown that plants deficient in potassium are more susceptible to frost. Soils that are deficient in potassium could benefit from increasing potassium levels at the start of the growing season. However it is unlikely that there will be a benefit of extra potassium applied to plants that are not potassium-deficient. Frost tolerance can not be bought by applying extra potassium or copper to a crop that is not deficient. There is no evidence that applying other micronutrients has any impact to reduce frost damage.
Step 3: Modify soil heat bankThe soil heat bank is important for reducing the risk of frost (Figure 4). Farming practices that manipulate the storage and release of heat from the soil heat bank into the crop canopy at night are important to consider to reduce the impact of a frost event. Agronomic practices that may assist with storing heat in the soil heat bank include:
- Practices that alleviate non-wetting sands, such as clay delving, mouldboard ploughing or spading, have multiple effects; these include increasing heat storage, nutrient availability and infiltration rate.
- Rolling sandy soil and loamy clay soil after seeding can reduce frost damage. It also prepares the surface for hay cutting should it be necessary.
- Reducing the amount of stubble: stubble loads above 1.5 t/ha in low production environments (2–3 t/ha) and 3 t/ha in high production environments (3–5 t/ha) generally increase the severity and duration of frost events and have had a detrimental effect on yield under frost.
- Halving the normal seeding rates can reduce frost severity and damage by creating a thinner canopy and more tillers resulting in a spread of flowering time. However, weed competitiveness can be an issue.
- Cross-sowing/seeding. Crops sown twice with half the seed sown in each direction have a more even plant density. Heat is released from the soil heat bank more slowly to warm the crop canopy at head height in early morning when frosts are more severe. This practice, however, increases sowing costs.
Step 4: Select appropriate cropsCrop selection is an important factor to consider for frost-prone paddocks. Crops grown for hay are harvested for biomass and avoid grain loss from frost. Pasture rotations are a lower risk enterprise and oats are the most frost tolerant crop during the reproductive stage. Barley is more tolerant than wheat at flowering, but it is not known if barley and wheat have different frost tolerance during grain fill. Canola is an expensive crop to risk on frost-prone paddocks due to high input costs. Flower Power (DAFWA) and Yield Prophet are useful tools to match the flowering time of varieties to your own farm conditions.
Step 5: Manipulate flowering timesWhen wheat is sown in frost risk areas, a good tactic is to ensure the flowering window of the cropping program is spread widely. This can be done by using more than one variety and manipulating sowing date and varieties with different phenology drivers so crops flower over a wide window throughout the season. It should be noted that flowering later than the frost may result in lower yields in seasons with hot, dry finishes due to heat and moisture stress. Staging sowing dates over a 3–6 week period is recommended. If sowing just one variety, this would provide a wide flowering window. If sowing more than one variety: sow winter wheat first; then a long season spring wheat or a daylength sensitive wheat; then an early maturing wheat last; the whole wheat program is set to flower over a two week period, potentially exposing it to more frost risk but maximising the yield potential in the absence of frost. Even with this strategy in place it is possible to have more than one frost event that causes damage. Flowering over a wide window will probably mean that some crop will be frosted but the aim is to reduce extensive loss. Sowing at the start of a variety’s preferred window will achieve higher yields at the same cost as sowing late. Sowing time remains a major driver of yield in all crops with the primary objective to achieve a balance between crops flowering after the risk of frost has passed but before the onset of heat stress. The loss of yield from sowing late to avoid frost risk is often outweighed by the gains from sowing on time to reduce heat and moisture stress in spring. To minimise frost risk there needs to be a mix of sowing dates, crop types and maturity types to be able to incorporate frost avoidance strategies into the cropping system. In years of severe frost, regardless of which strategy is adopted it may be difficult to prevent damage.Trials have found that blending a short season variety with a long season variety is an effective strategy. However the same effect can be achieved by sowing one paddock with one variety and the other with another variety to spread risks.
Step 6: Fine tune cultivar selectionNo wheat or barley varieties are tolerant to frost. Consider using wheat and barley varieties that have lower susceptibility to frost during flowering to manage frost risk of the cropping program while maximising yield potential. There is no point selecting less susceptible varieties for the whole cropping program if there is an opportunity cost of lower yield without frost. Preliminary ranking information for current wheat and barley varieties for susceptibility to reproductive frost is available from the National Variety Trial. A new variety should be managed based on how known varieties of similar ranking are currently managed.
Management tactics within seasonThe progress of the season should be monitored by regularly assessing weather forecasts and crop development in relation to frost incidence. Decisions may need to be made to implement in-crop management tactics to mitigate frost damage during the season.
GrazingThe key message is to graze early (at the crop four-five leaf stage or even earlier) and graze hard for a short period. Fourteen days grazing delays flowering by about seven days. Grazing after first node (GS31) will significantly delay flowering and reduce crop yield. High stock numbers are often required. Trials in southern WA and SA have shown grazing wheat crops in winter to delay flowering can reduce grain yield losses from spring frosts by extending the flowering date. Additionally these crops can provide extra fodder for livestock.
Extra nutrientsConservative input strategies should be adopted for frost-prone areas and minimal or no additional nutrients should be applied during the season. Manage nitrogen to frost risk. Avoid late nitrogen top-ups in zones and paddocks that have been identified during pre-season planning as having higher frost risk. Copper is the only exception. Tissue test for copper during tillering and apply foliar copper at booting if tissue samples are identified as marginal.
Post-frost event management tacticsOnce a frost event (especially at or after flowering) has occurred, the first step is to inspect the affected crop and collect a (random) sample of heads to estimate the yield loss incurred. In the event of severe frost, monitoring needs to occur for up to two weeks after the event to detect all the damage. After the level of frost damage is estimated the next step is to consider options for the frost damaged crop. Option 1: Take through to harvest If the frost is prior to or around (growth stage) GS31 to GS32, most cereals can produce new tillers to compensate for damaged plants provided spring rainfall is adequate. Tillers already formed but lower in the canopy may become important and new tillers can grow after frost damage, depending on the location and severity of the damage. These compensatory tillers will have delayed maturity, but where soil moisture reserves are high, or it is early in the season, they may be able to contribute to grain yield. A later frost is more concerning, especially for crops such as wheat and barley, as there is less time for compensatory growth. The required grain yield to recover the costs of harvesting should be determined using gross margins.
Option 2: Cut and baleThis is an option when late frosts occur during flowering and through grain fill. Assess crops for hay quality within a few days of a frost event and be prepared to cut a larger area than originally intended pre-season. Producing hay can also be a good management strategy to reduce stubble, weed seed bank and disease loads for the coming season. This may allow more rotational options in the following season to recover financially from frost, for example to go back with cereal on cereal in paddocks cut early for hay. Hay can be an expensive exercise. Growers should have a clear path to market or a use for the hay on farm before committing.
Option 3: Grazing, manuring and crop toppingGrazing is an option after a late frost, when there is little or no chance of plants recovering, or when hay is not an option. Spraytopping for weed seed control may also be incorporated, especially if the paddock will be sown to crop the next year. Ploughing in the green crop is to return organic matter and nutrients to the soil, manage crop residues, weeds and improve soil fertility and structure. The economics need to be considered carefully. Information sourced from GRDC.
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