Local topography has a large role in determining if and where frost develops. Cold air will settle in the valleys since it is heavier than warm air, therefore frost conditions are more prone in these regions. Valleys also shelter the area from stronger winds, enhancing the potential for frost.
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What is the function of resorcinol in the seliwanoff's test? Why do you think the exact nature of Gatsby criminal associations remains ambiguous? Get the Answers App. This can result in white bleached heads after a hot day. Lodging of cereals can also be an issue if windy conditions occur during late grain filling stages.
Stem frost damage late in grain filling can be confused with root diseases such as crown rot, rhizoctonia or septoria. All winter grain and oilseed crops are susceptible to frost.
It is therefore important to consider less susceptible crop species for frost-prone paddocks. The order of susceptibility for cereals is most to least ; durum, triticale, wheat, barley, cereal rye and oats. Wheat is more susceptible then barley at flowering, but barley is as or more susceptible during grain fill. Field peas are the most frost susceptible pulse crop followed by faba beans and lupins. However, due to its indeterminate nature, canola has a good capacity to recover from frost, given a favourable finish.
Canola is an expensive crop so careful consideration needs to be made for frost prone paddocks. Grain and oaten hay crops are the least susceptible to frost. Oats are less susceptible to frost during the reproductive stage than other cereals and as hay production requires biomass, reproductive frost damage will not reduce yield and may in fact improve the quality of the product through the mobilisation of sugars.
Pasture rotations are also lower risk enterprises. Position in the landscape influences temperature variations, frost damage and yield more than management practices. High production areas in a paddock are often lower in the landscape with the increased moisture and better soil types promoting higher yields.
Current frost research indicates that crops sown with high seeding rates, high nitrogen and higher yield potentials may be more susceptible to frost. It is thought that high inputs creates denser canopies which shades the soil, minimising soil heat retention and the ability of the soil heat bank to buffer the frosts.
There is also more synchronisation of the canopy development so a greater portion of the canopy may be exposed. As a result these crops can experience greater frost severity, duration and damage compared to crops grown with more conservative approaches. Despite this conservative nitrogen strategies are only recommend for the more severe frost prone parts of the landscape as the opportunity cost of these strategies often out ways the direct cost from frost damage. All wheat varieties are susceptible to frost however their risk profile during flowering can differ.
The frost performance values provided on the National Variety Trial website give an indication of a varieties risk to frost damage during flowering. Variety choice and time of sowing is a major driver of variation in yield and is still the most reliable way of reducing yield losses from frost.
To minimise the impact of frost, first select varieties adapted to your region and then match to the appropriate sowing time to ensure an optimum flowering period. Sowing the correct variety early can lengthen the growing season and deliver increased yields. However, when sowing early, it is critical to choose a variety that flowers during the optimum flowering window refer to Flower Power tool in WA or local agronomic material.
Consider using multiple varieties with different flowering times to target flowering throughout the optimal flowering period for your location to minimise the impact of frost. This can decrease the impact of sporadic frosts that occur within the optimal flowering window in some years. All wheat and barley varieties are susceptible to frost.
Using these values enables the direct comparison of the relative flowering frost susceptibility between multiple varieties. The lower the frost performance value, the lower the frost susceptibility of that variety. A new variety should be managed in terms of position in landscape, paddock selection etc, based on a growers experience with a known variety with similar FPV.
However, there is no economic benefit in selecting less susceptible varieties for the whole cropping program in the absence of frost. The soil heat bank refers to the amount of heat absorbed and retained by the soil during the day. This heat is then radiated back into the crop canopy overnight to warm flowering heads, minimising frost damage.
The amount of heat stored depends on a number of factors such as row spacing which affects canopy closure, soil colour, stubble loads and soil moisture. A moist soil profile will store more heat than a dry soil. Research has shown that by reducing stubble loads, there is a reduction in the severity and duration of frost events, resulting in less frost damage and better yields under frost conditions. No differences were observed between stubble height, orientation or composition.
In terms of minimising frost risk, a good rule of thumb is that stubble loads should match target grain yield. This calculation assumes a harvest index of 0. Current research shows that without frost, once off stubble reductions after opening rains at or just prior to seeding did not reduce yield and in the absence of frost often give a slight improvement in yield due to reduced disease and less nitrogen tie up, depending on site, season and variety choice.
With multiple severe frost events, stubble reduction does not increase yield in the most frost prone parts of the landscape, but may in the moderately prone areas Smith et al.
Here are a few frost forecasting methods;. Measure your dew point. This is the temperature at which water vapour starts condensing dew forms.
The dew point that is measured around 3pm can be taken as a useful first-estimate of the overnight low, for those nights with no air-mass change. The air temperature can be expected to cool to this value or lower on a clear calm long night.
There are not many devices around that can directly measure dew point. One way is to measure the wet bulb temperature and then use tables. Remember to keep the RH probe outside, and if you wish to measure the air temperature at the same time then use a thermometer that is properly housed in a Stevenson screen.
Deducting 4 degrees from an estimated overnight low of 1degC gives an estimated ground minimum temperature of -3degC, and that is a moderate frost which can be damaging in spring. Once the dew point is reached there may be some further cooling on a calm clear night longer than 12 hours and then the air temperature and dew point may fall in tandem, as this graph shows below right.
Use an empirical formula. There are many around. A former New Zealand Meteorological Service Chief Meteorologist, Ray Smith, wrote a Technical Note in researching an empirical formula for forecasting the ground minimum in Canterbury on clear calm spring nights:. This calculation can be considered to be a fine-tuning of method 1. Method 3. Extrapolate the changing temperature during the night. Once the night has set in and the temperature has started falling it tends to only fall at a rate determined by Newton's law of cooling.
Bill Ireland www. Method 4. Be forewarned. The amount of frost that occurs varies a lot from paddock to paddock and even within a paddock, so if you can build up some local knowledge of how your place varies in comparison with one of the MetService monitored sites, then we can help:.
So get out there and start measuring and use these techniques to help forecast your overnight frost. New Plymouth. Palmerston North. Chatham Islands. Stewart Island.
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