From VOA Learning English, this is the Agriculture Report.
这里是美国之音慢速英语农业报道。
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.
各种土壤保护的办法可以帮助农民防止其土地受到耕作和大自然力量的损害。土壤保护的办法之一是采用防风林。防风林是由树木和其它植物形成的屏障，农民在其农田四周种植防风林。
Windbreaks help prevent the loss of soil.
防风林有助于防止土壤流失。
They stop the wind from blowing soil away. They also keep the wind from damaging or destroying crops.
它们可以防止风把土壤吹走，还能防止风损毁庄稼。
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.
防风林在保护粮食作物方面极具价值。例如，关于西非部分地区防风林的研究已经完成。研究发现，与没有防风林的农田相比，防风林保护下的农田的粮食收成增长了20%以上。
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.
但关于防风林还有一些有趣的东西。似乎允许部分风穿过农田周围的树木或植物屏障时，防风林起到的效果反而更好。如果不允许风穿过，那么贴近地面的风就会吹起土壤，这样土壤就会被风吹走。
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，如果防风林只包含60%到80%的可以组成一道坚固防线的树木或植物，它所起到的效果最好。要记住一个简单的原则，防风林可以保护的农田宽度可以达到其最高树木高度的十倍。
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.
每片防风林至少要有2行。其中一行是大树，挨着的另一行可以是矮树或其他带叶子的植物。当地生长的树木或植物被认为是建造防风林的最佳选择。
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，某些种类的树木即使在贫瘠的土壤也能生长得很好。其中一种是白松，另一种是火炬松。
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土地和农作物免受风灾。多余的树木还能砍下来用作木材或出售。
Trees reduce the damaging effects of wind and rain. Their roots help protect soil from being washed away. And trees can provide another valuable service for agriculture. They can provide grazing animals with shade from the sun.
树木能够减少风雨的破坏性影响。它们的根系有助于防止土壤流失。同时树木能够为农业提供另一种极具价值的服务，他们能够为放牧牲畜提供荫凉处。
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