Học tiếng Anh: http://www.facebook.com/Words.and.Idioms hiệu quả, nhanh chóng: Các chương trình của VOA Learning English for Vietnamese (http://www.voatiengviet.com/section/hoc-tieng-anh/2693.html) có thể giúp các bạn cải tiến kỹ năng nghe, hiểu rõ cấu trúc và ngữ pháp, và sử dụng Anh ngữ một cách chính xác.
Luyện nghe nói tiếng Anh qua video: Chương trình học tiếng Anh của VOA: Special English Agriculture Report. Xin hãy vào http://www.voatiengviet.com/section/hoc-tieng-anh/2693.html để xem các bài kế tiếp.
From VOA Learning English, this is the Agriculture Report.
Farmers use soil conservation methods to protect their land from the damage caused by farming, wind and other forces of nature. Planting windbreaks is one method of soil conservation. Windbreaks are barriers formed by trees and other plants. Farmers plant these barriers around their fields. Windbreaks stop wind from blowing soil away. They also keep the wind from damaging or destroying crops. Windbreaks can be especially valuable for protecting grain crops. For example, researchers have studies windbreaks in parts of West Africa. They found that grain harvests were as much as 20 percent higher in fields protected by windbreaks. This method seems to work best when wind can pass through the barrier of trees or plants around a field. Without such protection, the movement of air close to the ground will lift the soil and blow it away. For this reason, a windbreak works best if it contains only 60 to 80 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 10 times the height of the tallest trees in the windbreak. 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 or other plants with leaves. Locally grown trees and plants are considered the best choices for windbreaks. Studies have shown that some kinds of trees can grow well even if the quality of the land is not very good. The white pine tree and the loblolly pine are examples. Windbreaks not only protect land and crops from wind. Older or extra trees can be cut down and used or sold for wood.