Page 62 - Irrigation Catalogue 2021 Bevo POL

MICRO AND SPRINKLERS
IRRIGATION & PROTECTION
FROST
PROTECTION
THERE ARE TWO KINDS OF FROST
Advection Frost (Windy Frost or Black Frost) occurs when a cold air mass (cold front) moves into an area, bringing freezing temperatures. Wind speed is usually above 8 km/h. Possible protection against this kind of frost is very limited.
Radiation Frost occurs when, with a clear sky and calm winds, the temperature near the surface of the earth drops to below freezing point. As temperatures drop, the cold air flows downward to lower topographic areas. That is where most of the damage is seen. Efforts have been made to come up with a solution for this kind of frost; a way to alleviate the damage caused by the low temperatures. In order to do so, we utilise the same basic laws of nature that play an impor- tant role in creating the frost itself.
Many methods have been used to protect fields and plantations from frost, including smokers, wind machines, helicopters, the burning of tyres and the use of sprinklers. Some methods have been more successful than others. The use of sprinklers was found most efficient in most cases.
LATENT HEAT ABSORBED
MELTING FREEZING
EVAPORATION CONDENSATION
FEST (EIS) LIQUID WATER LATENT HEAT RELEASED
GAS (WATER VAPOR)
FROST PROTECTION BY SPRINKLER
There are different ways to use sprinklers for frost protec- tion, taking many factors into account. However, the same thermodynamic principles apply to all methods of irrigation: A minimum application rate of 3.0 mm/h is required. This
is enough to provide protection at temperatures as low as -3°C. Another 0.5 mm/h is required for every additional degree, i.e. if the temperature is -4.0°C, the minimum application rate will be 3.5 mm/h (35 m3/ha/hour).
METHODS OF WATER APPLICATION
Overhead sprinkler irrigation is a very common practice in frost protection. Overhead irrigation provides excellent
frost protection at temperatures of -7°C and lower if the application rates are sufficient and the application is uniform. Drawbacks of this method are extensive water consumption; ice loading can cause branch damage; and root disease can be a problem in poorly drained soils. Water logging and soil erosion may also be a problem due to the large amount of water needed for overhead full cover frost protection.
Conventional overhead sprinkler systems use standard impact sprinklers to completely wet the plants and soil. Sprinkler distribution uniformity is important to prevent inadequate coverage, which might result in damage. In most cases, the sprinkler heads should be mounted at 30 cm or higher above the top of the plant canopy to prevent the plants from blocking the spray.
For frost protection, specially designed springs are often used, which are protected by an enclosure to prevent the icing of the heads. In short, the conventional overhead full cover method, when applicable, provides excellent protection and is the most common and safest frost protection solution. Wildly used in open field crops,
all kinds of orchards, blueberries and more.
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60 IRRIGATION CATALOGUE