Frost Protection - UTL Repository

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F R O S T P R O T E C T I O N : F U N D A M E N T A L S , P R A C T I C E A N D E C O N O M I C S
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katabatic (i.e. cold air drainage) flows. Cold air accumulates in depressions,
where the air becomes vertically stratified with temperature increasing with
height. In radiation frosts, higher night-time temperatures are observed on
hilltops and on upper middle sections of hillsides that are free from obstacles
to block cold air drainage.
SITE SELECTION FACTORS FOR RADIATION FROST EVENTS
1 Due to cold air drainage to low spots, night-time minimum temperatures
tend to follow topographical contours.
2 Large water bodies upwind tend to diminish frequency of frost events.
3 Rocky masses (cliffs) and canopy covers (i.e. taller nearby plants) can
increase downward night-time radiation and increase minimum
temperatures. However, in some locations, they can block cold air
drainage and favour stratification and cold air ponding. Every location is
unique and the advantages and disadvantages of proximity to rocky
masses and canopy covers must be considered separately at each location.
4 Soil type affects energy storage and release and hence night-time temperature.
5 Local topography and landscape obstacles affect cold air drainage.
Site selection is the single most important method of frost protection. Factors
to consider are cold air drainage, slope and aspect, and soil type. Most growers
are aware of some spots that are more prone to damage than others. Typically,
low spots in the local topography have colder temperatures and hence more
damage. However, damage can sometimes occur in one section of a cropped area
and not in another without apparent topographical differences. In some cases,
this might be due to differences in soil type, which can affect the conduction and
storage of heat in the soil. Of course, management of the soil and cover crops can
also affect heat storage and damage. Although not commonly cited as a site
selection factor, proximity to grasses and other plants with high concentrations
of ice-nucleating bacteria can also be a factor affecting frost damage.
FACTORS AFFECTING COLD AIR DRAINAGE
1 Obstacles should be removed that inhibit down-slope drainage of cold air
from a crop.
2 Land levelling can improve cold air drainage and eliminate low spots that
accumulate cold air.
3 Row lines in orchards and vineyards should be oriented to favour natural
cold air drainage. However, the advantages from orienting crop rows to
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