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  3. Modified Agricultural Practices Since agriculture accounts for nearly 70 percent of the world’ s fresh water withdrawn from

Modified Agricultural Practices Since agriculture accounts for nearly 70 percent of the world’ s fresh water withdrawn from

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问题     Modified Agricultural Practices
    Since agriculture accounts for nearly 70 percent of the world’ s fresh water withdrawn from rivers , lakes, and underground aquifers for human use, the greatest potential for conservation lies with increasing irrigation efficiency. By reducing irrigation by 10 percent, we could double the amount available for domestic water worldwide. This can be done by converting to water-conserving irrigation systems; taking the poorest and steepest lands out of production; switching to less-thirsty crops (which may require changes to government subsidies for certain crops) ; implementing proper agricultural land drainage and soil management practices, and reducing fertilizer and pesticide use.
    Typically, governments provide water to large commercial farmers at greatly subsidized rates, decreasing the need for conservation and promoting wasteful practices. This has led to widespread use of wasteful irrigation systems. Studies show that just 35-50 percent of water withdrawn for irrigated agriculture actually reaches the crops. Most soaks into the ground through unlined canals, leaks out of pipes, or evaporates before reaching fields. Although some of the water lost in inefficient irrigation systems returns to streams or aquifers where it can be tapped again, water quality is invariably degraded by pesticides, fertilizers and salts. This is in fact another way that commercial agriculture "uses" water: by polluting it so that it is no longer safe to drink. In areas where commercial agriculture is prevalent, runoff from farms has poisoned water supply with dangerous levels of toxics.
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答案 改良的农业耕作 从全世界河流、湖泊和地下蓄水层汲取的供人类使用的淡水中，有近70％是用于农业，因此节水的最大潜力在于提高农业灌溉效率。减少10％的灌溉用水，我们就能够使世界各地的家庭用水量增加1倍(翻一番)。我们可以改用节水的灌溉系统，停止耕种最贫瘠、最陡峭的土地，再种植耗水量较低的植物(这可能会要求改变政府对某些农作物的津贴额)；采取适当的农业土地排水及土壤管理办法；减少化肥和杀虫剂的使用。 通常，政府以很高的津贴优惠向大户的商业性农民供水，这就削弱了节水的必要性，鼓励了浪费行为。这种做法已导致农民广泛使用浪费水资源的灌溉设备。研究表明，农业灌溉用水中只有35％～50％真正用在农作物上。大部分的水通过没有铺衬里的灌溉渠道浸入土壤，或从水管泄漏出来，或在到达农田之前就蒸发掉了。尽管从低效的灌溉系统中损失的部分水，会重新返回可再次利用的河流或地下蓄水层中，但其水质因杀虫剂、化肥和盐份的渗入却不可避免地下降了。这实际上就是商业性农业“使用”水的另一种方式：对水造成污染，使水无法再安全饮用。在商业性农业盛行的地区，从农田中流出的水已经污染生活供水，使得水中的有毒物质达到危险的程度。
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