85 Protecting the Orange Crop

Frost on the windows is a child's dream. Frost in the orange groves is a grower's nightmare. Here is the reason: frost can ruin the oranges and even kill the trees. How does this happen? When the temperature is below 32 degrees Fahrenheit, juices in the leaves and oranges freeze. When it freezes, the juice expands. This swelling bursts the thin cells of the leaves and fruit. Then, they act fast. Smudge pots and trees dry up. When growers hear a forecast of frost, the oranges are ready for lighting are placed in the groves. Oil burners are also put out. Both are costly. For example, to protect an orange grove, 20 to 100 heaters are needed per acre.

Smudge pots and heaters are two ways of fighting frost. But now there is a new way. Odd as it sounds, growers use ice to fight freezing. Some spray their crops with water on a freezing night. The water freezes quickly, and then a strange thing happens. As long as ice stays wet, it can never become entirely frozen. Trees and oranges can stand this temperature. If the ice ever got colder than 32 degrees and dry, it might drop many degrees and ruin the crop. The trick is to continually spray water on the ice. The spraying keeps the temperature from going below 32 degrees even if the air is much colder. Jack Frost may be frustrated, but the oranges and trees are saved.

This strange kind of "ice blanket" works only on plants strong enough to stand the weight of frozen spray. The system is also used to protect banana plants on some Central American plantations.

85 保护柑橘作物

窗上的霜是孩子的美梦，而柑橘园里的霜却是种植者的噩梦。原因如下：霜冻会毁坏柑橘，甚至杀死树木。这是怎么发生的呢？当气温低于华氏32度时，树叶和柑橘里的汁液会结冰。结冰时，汁液会膨胀，这种膨胀会撑破树叶和果实的薄壁细胞。之后，种植者会迅速行动，烟雾罐和树木都要做好干燥准备。当种植者听到霜冻预报时，会在果园里放置照明设备，也会点燃燃油加热器。这两种方法都很昂贵，例如，要保护一片柑橘园，每英亩需要20到100个加热器。

烟雾罐和加热器是对抗霜冻的两种方法，但现在有了一种新方法。听起来很奇怪，种植者在冰冻的夜晚用水喷洒作物来抵御霜冻。水会迅速结冰，然后发生一件奇怪的事：只要冰保持湿润，就永远不会完全冻结。树木和柑橘可以承受这种温度。如果冰的温度降到32度以下且变干，可能会骤降很多度，从而毁坏作物。诀窍是持续向冰上喷水，这样即使空气温度低得多，也能让温度保持在32度以上。杰克霜（霜冻的拟人化说法）可能会受挫，但柑橘和树木得以保全。

这种奇怪的“冰毯”只在足够强壮、能承受冰冻喷雾重量的植物上有效。该系统也被用于中美洲一些种植园的香蕉植株保护。