粘膜下肌瘤宫腔镜电切:土地沙漠化现状、速度及治理方法

不合理的土地利用使沙漠化处于发展过程中，欲求受沙漠化影响地区可持续发展和沙漠化的防治，根本出路在于合理高效的土地利用。根据我国北方沙漠化地区自然资源环境、社会经济特点，土地开发利用中存在的问题和沙漠化治理的典型经验，沙漠化土地的防治必须本着经济效益、生态效益和社会效益统一的目标，建立既可防止土地沙漠化，又可促进生产发展的资源节约型、适度开发型和环境保护型的经济体系。
　　在沙漠化土地治理的具体措施上，在农牧交错地区可针对沙区中居民点、耕地、草场相对分散分布的特点，可以生态户为基础，采取天然封育，调整以旱作农业为主的土地利用结构，扩大林草用地比重，集约经营水土条件较好的土地，并和营造防风沙林带、林网及沙丘表面栽植固沙植物、丘间地营造片林或封育相结合的措施；在草原牧区，除了合理确定草场载畜量，轮牧和建立人工草地及饲料基地外，还应与合理配置水井，确定放牧点密度，修建牧道等结合起来；在干旱地带，要以内陆河流域为生态单元进行全面规划，合理确定用水计划，以绿洲为中心，建立绿洲内部护田林网、绿洲边缘乔灌结合的防沙林带和绿洲外围沙丘固定等措施相结合，形成一个完整的防治体系。
　　许多实践证明了合理的土地利用是可以达到土地沙漠化的防治及可持续利用的目的的。以陕西省榆林地区为例[5]，据史书记载，在 1500 年前，榆林地区还是个林草茂密，宜农宜牧之地。后因历代征战摧残，乱砍滥伐，植被覆盖率仅有 1.8%，流沙已越过长城，逼近榆林城。据调查，在解放前的 100 多年时间里，有近 13.4万hm2 农田和草场院由于沙漠化而被放弃，11.3万hm2 农田和 26.7万hm2 草场受到沙漠化的威胁，产量和载畜量低而不稳。自 50 年代以来，通过统一规划、调整和优化土地利用结构，坚持以治沙造林、保护和发展农牧业为主导，取得了很好的生态、经济和社会效益。从 1950 年到 1990 年底，榆林治沙造林保存面积达 74.0万hm2，恢复和改良草场 66.7万hm2 多。粮食总产量 1990 年较 1950 年增产 6 倍，大家畜由 7.6 万头增加到 36.3 万头，羊由 36 万只增加到 150 万只，活立木蓄积 340万m3，价值 7 亿多元，有 5 万多农户脱贫致富。

Desertification occurs when the land loss it productivity and become barren.

There are four solutions to solve the problem. They are reforestation, crop rotation, control grazing and lastly education.

Firstly, reforestation is the planting of trees and other vegetations to hold the top layer soil, which is the most fertile soil for cultivation. This is to prevent soil erosion as we can refer to the desertification which happened near Beijing. This can be highlighted as the reforestation method had cut down 3% of soil erosion in northern China.

Nextly, the crop rotation method is planting of different crops on a same piece of land every year. This can retain the fertility of land and some crops may also provite nutrients for the next crops that are going to plant the following year. The other way is to left one piece of land to rest and switch with the planted land every year.

In addition, controlled grazing is important for nomadic herders or sedentary pastoral farmers. This method is similar to the second way of crop rotation.

Lastly, education is also a major process in preventing desertification. By educate the people the above three methods we can ensure that our farms will not damage the land especially cautiou in semi-arid areas.