The area of desert in the world is growing every year. Many parts of the world which once had large populations and produced plenty of crops, have become deserts. Dunhuang in China, deep in the heart of the Gebi Desert, was once a great city.
Cattle are one cause of the problem. In good years, famers increase the numbers of their cattle. Then one year, the rains fail to come. The farmers do not want to kill any of their cattle, so the cattle eat ail the grass and anything that grows on poorer land. If this continues for several years, the grass never grows again and the land becomes a desert. One suggested answer is for farmers to limit the numbers of their cattle.
Another problem is that good soil is gradually lost. When trees are cut down, there is nothing to hold the soil in place on the hillside. So when if rains, the soil is washed down the hills and into the rivers. Strong winds can also blow away the valuable soil that lies on the top of the fields.
世界上沙漠的面积每年都在扩大，许多地区曾经人口众多，五谷丰登，而今却成了沙漠。中国的敦煌曾经是一个大城市，而现在却深深陷入戈壁滩的腹地。
造成戈壁滩的原因之一是牲畜问题。年景好时，农民就增加牲畜饲养的头数。后来有一年天没有下雨，农民又不想把牲畜杀掉。因此，牲畜就把草和更加贫瘠的土地上所长的任何东西全都吃光。这种情况如果继续几年，那么，草就再也长不出来了，土地也就变成了沙漠。有人提出的解决办法是让农民限制饲养牲畜的数量。
另外一个问题就是沃土逐渐流失。树木被砍伐了，山坡上就没有什么东西能够把土壤保持住了。因此，下雨的时候，土壤从山上被冲刷下来，流到河里去了。大风也可能把田地表面的肥沃土壤刮走。
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