[ti:To Help Your Plants, Use Less Salt]
[by:www.21voa.com]
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[00:00.04]In the United States, people often use large amounts of salt
[00:06.36]to remove dangerous ice from roads and walkways in the winter.
[00:12.68]But when the spring arrives,
[00:15.88]all that salt can really damage plants in the garden.
[00:21.36]Salt is the chemical sodium chloride.
[00:25.80]Salt pulls water from living cells,
[00:29.96]like plant roots and the healthy ground soil around them.
[00:34.88]So, spring growth may show up lighter in color than normal,
[00:40.36]or, in the worst cases, plants may simply die.
[00:46.04]Rain can wash away much of the salt,
[00:49.48]permitting some older plants to live.
[00:52.60]Salt can also be removed by pouring a large amount
[00:56.92]of water on the ground where plants are growing.
[01:00.84]But the best action is to simply use less salt.
[01:06.80]Researchers have found that putting a small amount of salt on a road
[01:12.16]works better to melt ice than dropping a large amount of salt crystals.
[01:18.96]There are, of course, other things that can be used in place of sodium chloride.
[01:25.64]One is the chemical calcium chloride.
[01:29.48]It does less damage to plants and melts ice faster than salt.
[01:35.32]It also works when the temperature is below negative 17 degrees Celsius.
[01:43.52]Salt loses some of its effectiveness at temperatures below negative 12 degrees.
[01:50.72]Still, calcium chloride does put chloride ion,
[01:56.04]which plants don’t like, into the soil.
[01:59.36]It is also more expensive and can do more damage to cars.
[02:04.52]Man-made chemical fertilizers are all salts.
[02:09.36]So why not use them to remove ice from the roads?
[02:14.00]Well, they are even more costly,
[02:16.96]and they only work at negative 6 degrees Celsius.
[02:21.84]Calcium magnesium acetate, also called CMA,
[02:27.48]has become a popular alternative.
[02:30.88]It is made by combining limestone, a type of rock, and vinegar.
[02:37.32]It breaks down naturally so it does not damage plants or soil.
[02:43.28]It stays on roads and does not hurt cars.
[02:48.24]CMA does have problems, however.
[02:51.60]It is most effective at around negative 9 Celsius, just like salt.
[02:57.96]And it is better at stopping ice from forming rather than removing it.
[03:03.76]So, it is best placed on a road before the temperature gets very cold.
[03:09.68]Some materials other than salt - such as sand or very small pieces of wood
[03:16.64]- can also work against ice. But they can be very messy.
[03:21.76]The best way to remove ice is through a holistic method.
[03:26.96]This involves using a combination of materials,
[03:31.24]such as salt and a bit of sand.
[03:34.44]If this mixture is used before ice forms,
[03:38.44]less is needed as the weather gets colder.
[03:41.76]When placing plants in the ground near a road or where a car is parked,
[03:47.76]it is best to use common sense:
[03:50.92]choose a plant that is not badly affected by salt.
[03:55.72]Plants that are native to the seashore can usually stand up well to salt,
[04:01.56]like Rosa rugosa, a common beach rose.
[04:06.24]Other examples of trees and plants that can resist the effects of salt
[04:11.68]include silver maple, honey and black locusts,
[04:16.60]poplar, junipers, lilac and Colorado blue spruce.
[04:22.40]I’m Susan Shand. 更多听力请访问21VOA.COM