VOA慢速英语:Building a Windbreak to Protect Crops

Soil conservation methods help farmers protect their land from the damage caused by farming and the forces of nature. One method of soil conservation is the use of windbreaks. Windbreaks are barriers formed by trees and other plants. Farmers plant these barriers around their fields.
土壤保护方法可以帮助农民保护农田免受来自耕种和自然力所造成破坏。其中一种土壤保护的方法就是使用防风林。防风林是由树木和其他植物形成的屏障。农民在各自的农田周围种植这些天然的屏障。

Windbreaks help prevent the loss of soil.
防风林有助于防止土壤流失。

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They stop the wind from blowing soil away. They also keep the wind from damaging or destroying crops.
防风林可以防止风将土壤吹走，还可以防止风损害或摧毁农作物。

Windbreaks can be highly valuable for protecting grain crops. For example, studies have been done on windbreaks in parts of West Africa. These studies found that grain harvests were as much as twenty percent higher in fields protected by windbreaks compared to fields without them.
防风林对保护谷类作物非常有价值。例如，研究小组已经完成对西非部分地区防风林的研究。研究发现，有防风林保护的农田的谷物产量比没有防风林保护的农田高20%。

But here is something interesting about windbreaks. They seem to work best when they allow some wind to pass through the barrier of trees or plants around a field. If not, then the movement of air close to the ground will lift the soil. Then the soil will be blown away.
但是，这里有一些关于防风林有趣的现象。防风林允许一些风穿过树木屏障进入农田的时候效果最好。否则，接近地面的空气流动会使土壤上升，土壤仍然会被吹走。

For this reason, a windbreak works best if it contains only sixty to eighty percent of the trees and plants that would be needed to make a solid line. An easy rule to remember is that windbreaks can protect areas up to ten times the height of the tallest trees in the windbreak.
出于这个原因，如果防护林中栽种的树木只有组成坚固的屏障所需的60%到80%，效果是最好的。需要记住的一个简单的规则是，防风林可以保护的范围是其中最高的树木高度的十倍。

There should be at least two lines in each windbreak. One line should be large trees. The second line, right next to it, can be shorter trees and other plants with leaves. Locally grown trees and plants are considered the best choices for windbreaks.
每个防风林至少应该要有两行树木。其中一行应该是大树。旁边的第二行可以是比较矮的树木或者有叶子的其他树木。当地种植的树木和植物被认为是用于防护林的最佳选择。

Studies have shown that some kinds of trees can grow well even if the quality of the land is not very good. One kind of tree is the white pine. Another is the loblolly pine.
有研究表明，即使在质量不怎么好的土地上，一些树木也能良好地生长。其中一种就是白松，另外一种是火炬松。

Windbreaks not only protect land and crops from the wind. Surplus trees can be cut down and used or sold for wood.
防风林不仅可以保护农田和作物免受风的损害。多余的树木还可以进行砍伐，自己使用或者作为木材出售。

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Trees reduce the damaging effects of wind and rain. Their roots help protect soil from being washed away. And trees can provide another service for agriculture. They can provide grazing animals with shade from the sun.
树木可以减少风雨的破坏性影响。树木的根系有助于防止土壤被冲走。树木还可以为农业提供另外一种宝贵的资源，为畜牧动物提供树荫。