Cropping Frost
Photo: Catriona Nicholls
Growers walk the wire as frost bites As many cropping areas head towards flowering, growers are on edge when it comes to managing frosted crops. Having a plan in place could make the difference between devastation and profitability according to frost expert Garren Knell. Catriona Nicholls
Photo Melissa Rebbeck SARDI - Climate Applications
kondinin group
Frost, like drought, death and taxes is something most growers can rest assured will continue to occur — and nothing can be done to prevent it. However, being aware of the risks and having a strategic plan in place can help growers make the most of a bad situation.
The first step is to understand the risks, identify the options and when frost occurs, to assess the extent of damage before taking any action. Frost bite: Frost-affected, banana-shaped anther.
At a glance Early identification of frost damage allows for greater flexibility of crop management options. Have a plan in place before frost damage occurs. Risk of damage is highest when crop heads have emerged and flowering is imminent.
In reality the options for a frost-damaged crop are few — play the waiting game and proceed to harvest, graze with livestock or cut for hay. According to frost expert Garren Knell, ConsultAg many growers across Western Australia are facing the lowest growing season rainfall on record. “In affected areas, growers faced with crop failure due to frost could find a valuable alternative in cereal hay,” Garren said. But while hay may seem like an easy, potentially profitable option, Garren cautions growers against leaving their decision too late.
Understanding frost A frost event and subsequent crop damage is determined by a combination of factors including: temperature, humidity, wind, topography, soil type, crop and variety, and crop stage. While some crop species are more frost tolerant (see Figure 1) all grain crops are susceptible to yield losses from frost.
Figure 1 Crop susceptibility to frost from most to least susceptible
Cereals
Frost damage is not always obvious — inspect 5–7 days after frost occurs. Canopy temperature is more critical than weather — in crop temperatures can be up to five degrees Celcius less than air temperature above the crop.
“There is a window of opportunity after frosting of about two weeks for optimal hay quality,” he said. “After this growers could be throwing good money after bad, particularly if haymaking experience and marketing is lacking.” Hay production for the inexperienced can be a costly exercise. To optimise the opportunity, the decision needs to be fast and a potential market already sourced. “For timely action, growers need to be aware when a frost event has impacted their crop and that may not be as clear cut as it seems,” Garren said. “For many growers frost often goes unobserved until grain fill and harvest.” A better understanding of the factors that combine to cause a frost event can be the difference between devastation and opportunity.
Triticale
Wheat
Field peas
Faba beans
Barley
Pulses
Source: GRDC
58 Farming Ahead September 2010 No. 224 www.farmingahead.com.au
Lupins
Cereal rye
Oats
Cropping Frost
Frost during flowering generally causes the most damage, but cereal crops are susceptible between booting and grain ripening (see Figure 2). Low temperatures at the grain head are of most concern. However standard weather stations are located 1.5 metres above the ground — well above most crops. Research reveals that a temperature recording of 2.2 degrees Celsius in a weather station can result in frost damage in flowering crops. The difference between canopy temperature and that recorded at the weather station can be as much as 5°C or more. At night, heat is lost (radiated) from the ground into the atmosphere, resulting in the soil surface and air surrounding the crop canopy cooling rapidly. Under calm conditions, when the atmosphere is relatively dry (dew point less than 2.2°C), a radiation frost can occur. “Radiation frost events are the main cause of damage to grain crops,” Garren said. “As cool air flows to the lowest point of the landscape it is these areas that are especially frost prone.”
Frost damage can occur even if a white coat of ice crystals is not apparent on the crop. Figure 2 Crop growth stage susceptibility to frost Germination — Cereals Seedling — Germination — Tillering — Seedling — Stem elongation — Tillering — Booting — Stem elongation — Ear emergence — Booting — Anthesis (flowering) — Ear emergence — Milk development — Anthesis (flowering) — Dough development — Milk development — Ripening — Dough development — Maturity — Ripening — LOW ! ! ! HIGH Maturity —
LOW ! ! ! HIGH
pulses and canola Germination — Seedling — Germination Bud formation Seedling — Bud Flowering formation — PodFlowering growth — fill — Pod Seed growth Ripening Seed fill — Maturity — Ripening Maturity —
Note: Diagrams not to scale Source: GRDC
LOW ! ! ! HIGH LOW ! ! ! HIGH
“In frost-prone regions, growers need to regularly monitor conditions and crops for signs of frost and record varieties, frost dates and the area of a paddock affected for future frost risk management.”
Timely tools A number of tools are available to growers wanting to take a proactive approach to frost monitoring and damage assessment. According to Garren, many WA growers in frost-prone areas are buying temperature data loggers to keep an eye on what is happening. “Data loggers are allowing growers to see what is happening in their paddocks and to identify just how low the temperatures are getting, and for how long, when crops are at their most sensitive,” Garren said. “It is important for growers to know their paddocks well, as a frost event rarely wipes out a crop in its entirety.” “Low-lying areas are much more prone to frost damage and the key is to identify just how widespread the damage has been before taking any action.” However, Garren reminds growers that frost appears to be spreading and events during the past 10 years have increased and been more severe than those experienced during the past. “In WA we are certainly seeing more frost-damaged crops and frost events in areas not usually expected to be frost prone,” Garren said. For growers who are concerned about frost, but not keen on investing in a data logger at this stage, Garren suggests trying out the Bureau of Meterology’s (BoM) new Frost Potential website. “Frost Potential is a web-based frostprediction tool with maps that show forecast low temperature thresholds for various Australian weather station locations,” he said. The maps are updated daily and show forecasts for the next 48 hours (see Farming Ahead July 2101, No. 222 for more information). Calculating the cost According to Garren, after a frost event has occurred growers need to determine their own fate in terms of options. “Determining the extent of damage and deciding on a strategy will be a matter of carrying out a cost–benefit analysis,” he said. “However, early identification is essential to achieve the optimum return from the crop, whatever the option.” Detailed frost identification guides for cereals, pulses and canola are available as part of GRDC’s ‘Back Pocket’ series and in the GRDC publication Managing Frost Risk. As a rule of thumb however, Garren recommends estimating the yield of the frost-damaged crop. The next step is to consider the following factors:
Atmospheric events leading to a frost include:
ressure system • A slow-moving high-p stream from a air d rlan ove directing an d speed and win t ligh dry air mass, with ht. rnig ove er cov d clou no h quite strong winds • A cold outbreak wit the afternoon. moves through during rapidly follows tem sys e sur res h-p A hig cold air mass y ver The . sion the depres atmospheric low in d win ‘decouples’ the l unstable stil the levels and very often ws fairly clear allo ss ma air the of nature the period just skies. Frost can form in before dawn. owed by a • A cold, cloudy day foll the cloud cover all ere calm night, wh disappears. perature after • A rapid drop in air tem starting around res atu 3pm (with temper o within 30 C 16oC and dropping to 15 vement). minutes with no air mo wpoint’. As the air • A gradual drop in ‘de evening, frost can the ing dur s drie ss ma t winds and clear ligh as g lon as develop skies prevail.
Harvestable grain — use gross margins to establish the grain yield required to recover harvest costs. Hay — determine the likely demand and opportunity for marketing hay from the frosted crop. Calculate the likely costs and returns from haymaking (Is machinery on hand or would contractors be required?) Consider the weed burden within the crop and the effect on hay quality and marketability. Livestock — Consider grazing the crop if livestock are available. Soil erosion — consider the impacts of potential soil erosion from any option. A detailed decision support process, including formule and methodologies, is covered in Managing Frost Risk – a Guide to Southern Australian Grains. more information Managing Frost Risk – a Guide to Southern Australian Grains and Frost identification – Back Pocket Guides are available from Ground Cover Direct www.grdc.com.au
When frost bites — a decision support fact sheet soon to be available from Ground Cover Direct www.grdc.com.au
GRDC research Contact Garren Knell, ConsultAg GK@consultag.com.au
Farming Ahead September 2010 No. 224 www.farmingahead.com.au
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