Sprinklers like the Xcel-Wobbler can protect crops during radiation frosts by covering them with a thin layer of water and letting the latent heat from the freezing process keep the plant above freezing temperatures.
Growers across the world have used heaters, wind machines, insulation and even helicopters to prevent frost damage as air temperatures start to drop below 32° F (0 °C). The impact of frost damage on production can be devastating to farmers and the local economy – but the good news is that it can be preventable.
How does Irrigation Help?
Damage due to radiation frost can be averted on solid set installations and nurseries with the use of overhead sprinklers.
Sprinklers like the Xcel-Wobbler and the mini-Wobbler can help plants maintain surface temperatures at 32° F (0 °C) by gently covering them with a thin layer of water that is consistently and uniformly sprayed over the plant. As the air temperature surrounding the plants drops below freezing, the water begins to freeze and crystallize, encasing the plant and partially isolating it from exterior temperatures. The heat energy released – 80 calories of heat for every 0.03 ounces (1 gram) of water that freezes – is absorbed by the plant to help it stay just above its freezing point.
For this to work, sprinklers must apply water over the entirety of the plant – including its tissue, branches, and buds – uniformly, constantly, and in rapid intervals to prevent the sudden removal of heat energy.
A uniform application pattern is crucial for maintaining a constant layer of ice over plants. Without an even application, ice will melt in certain areas and plant temperatures will fall, leading to supercooling and damage possibly worse than what a frost alone could cause.
Xcel-Wobbler deliver excellent coverage and uniformity (from 85% – 90%) through their 360° application pattern. Their constant rotary action prevents ice buildup, which prevents the sprinkler from freezing, and their uniform application pattern resists wind drift.
Wobblers protect plants with average flow rates of 1.3 gpm (295 L/hr) and only require pressures of approximately 20 psi (1.38 bar). Xcel-Wobblers can also be installed 6 to 16 ft (1.8 to 5 m) above the ground and spaced at distances of 30 x 30 ft (9.14 x 9.14 m) in some instances.
How are Sprinklers more Economical?
The operational costs, labor requirements and energy consumed by low-pressure sprinklers are considerably less when compared to other methods such as heaters.
With heaters, the average grower needs to generate approximately 6.1 million kilocalories per acre per hour (2.5 million kilocalories per hectare) to protect their plants. This would require approximately 458 lbs (208 kg) of liquid petroleum gas/propane, 61 gallons (230 liters) of petroleum, or 769 lbs (349 kg) of mineral carbon. This results in expenses of over $495 dollars for each acre or $200 dollars per hectare.
Senninger Xcel-Wobblers only need 5kW of electric power to distribute a layer of water of about 3 mm/hr, which is capable of generating the 6.1 million kilocalories per acre per hour (2.5 million kilocalories per hectare per hour) needed for effective frost protection.
For more information on frost protection with sprinklers, visit FAO.org and look over Frost Protection: fundamentals, practice, and economics.