Building a Windbreak to Protect Crops-英语听力

[00:00.100]From VOA Learning English, [00:02.410]this is the Agriculture Report. [00:04.950]Soil conservation methods help farmers [00:08.850]protect their land from the damage [00:11.240]caused by farming and the forces of nature. [00:15.200]One method of soil conservation [00:18.320]is the use of windbreaks. [00:20.680]Windbreaks are barriers formed by trees and other plants. [00:25.600]Farmers plant these barriers around their fields. [00:29.450](SOUND) [00:34.410]Windbreaks help prevent the loss of soil. [00:37.970]They stop the wind from blowing soil away. [00:42.330]They also keep the wind from damaging or destroying crops. [00:48.730]Windbreaks can be highly valuable for protecting grain crops. [00:54.990]For example, studies have been done on windbreaks [00:59.550]in parts of West Africa. [01:01.850]These studies found that grain harvests [01:05.810]were as much as twenty percent higher in fields protected [01:11.210]by windbreaks compared to fields without them. [01:15.470]But here is something interesting about windbreaks. [01:20.430]They seem to work best when they allow some wind to pass [01:25.830]through the barrier of trees or plants around a field. [01:30.440]If not, then the movement of air [01:33.750]close to the ground will lift the soil. [01:37.560]Then the soil will be blown away. [01:41.260]For this reason, a windbreak works best [01:45.480]if it contains only sixty to eighty percent of the trees [01:50.930]and plants that would be needed to make a solid line. [01:55.480]An easy rule to remember is that windbreaks [02:00.220]can protect areas up to ten times [02:03.670]the height of the tallest trees in the windbreak. [02:08.130]There should be at least two lines in each windbreak. [02:13.350]One line should be large trees. [02:16.700]The second line, right next to it, [02:19.970]can be shorter trees and other plants with leaves. [02:24.600]Locally grown trees and plants [02:28.150]are considered the best choices for windbreaks. [02:32.360]Studies have shown that some kinds of trees can grow well [02:37.760]even if the quality of the land is not very good. [02:42.710]One kind of tree is the white pine. [02:46.620]Another is the loblolly pine. [02:50.330]Windbreaks not only protect land and crops from the wind. [02:55.870]Surplus trees can be cut down and used or sold for wood. [03:02.890](SOUND) [03:05.790]Trees reduce the damaging effects of wind and rain. [03:11.050]Their roots help protect soil from being washed away. [03:15.890]And trees can provide another valuable service for agriculture. [03:22.150]They can provide grazing animals with shade from the sun. [03:27.260]And that's the Agriculture Report from VOA Special English.