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17年1月21日亞太SAT閱讀原文第五篇

2017-04-17來源: 互聯網浏覽量:
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  爲了幫助考生們更好地備考SAT閱讀考試,今天小編給大家帶來2017年1月21日亞太SAT閱讀原文第五篇,希望同學們看過之後對自己的備考有所幫助!

  Perennial Solution

  Annual grains feed the world, but they create problems. Perennials are thrifty. Their long roots hold on to soil, water, and fertilizer, which means less pollution.

  By Robert Kunzig

  Photograph by Rebecca Hale, NGM Staff

  Humans made an unwitting but fateful choice 10,000 years ago as we started cultivating wild plants: We chose annuals. All the grains that feed billions of people today—wheat, rice, corn, and so on—come from annual plants, which sprout from seeds, produce new seeds, and die every year. "The whole world is mostly perennials," says USDA geneticist Edward Buckler, who studies corn at Cornell University. "So why did we domesticate annuals?" Not because annuals were better, he says, but because Neolithic farmers rapidly made them better—enlarging their seeds, for instance, by replanting the ones from thriving plants, year after year. Perennials didn't benefit from that kind of selective breeding, because they don't need to be replanted. Their natural advantage became a handicap. They became the road not taken.

  Today an enthusiastic band of scientists has gone back to that fork in the road: They're trying to breed perennial wheat, rice, and other grains. Wes Jackson, co-founder and president of the Land Institute in Salina, Kansas, has promoted the idea for decades. It has never had much money behind it. But plant breeders in Salina and elsewhere are now crossing modern grains with wild perennial relatives; they're also trying to domesticate the wild plants directly. Either way the goal is crops that would tap the main advantage of perennials—the deep, dense root systems that fuel the plants' rebirth each spring and that make them so resilient and resource efficient—without sacrificing too much of the grain yield that millennia of selection have bred into annuals.

  We pay a steep price for our reliance on high yields and shallow roots, says soil scientist—and National Geographic emerging explorer—Jerry Glover of the Land Institute. Because annual root crops mostly tap into only the top foot or so of soil, that layer gets depleted, forcing farmers to rely on large amounts of fertilizers to maintain high yields. Often less than half the fertilizer in the Midwest gets taken up by crops; much of it washes into the Gulf of Mexico, where it fertilizes algae blooms that cause a vast dead zone around the mouth of the Mississippi. Annuals also promote heavy use of pesticides or tillage because they leave the ground bare much of the year. That allows weeds to invade.

  Above all, leaving the ground bare after harvest and plowing it in planting season erodes the soil. No-till farming and other conservation practices have reduced the rate of soil loss in the U.S. by more than 40 percent since the 1980s, but it's still around 1.7 billion tons a year. Worldwide, one estimate put the rate of soil erosion from plowed fields at ten to a hundred times the rate of soil production. "Unless this disease is checked, the human race will wilt like any other crop," Jackson wrote 30 years ago. As growing populations force farmers in poor countries onto steeper, erodible slopes, the "disease" threatens to get worse.

  Perennial grains would help with all these problems. They would keep the ground covered, reducing erosion and the need for pesticides, and their deep roots would stabilize the soil and make the grains more suitable for marginal lands. "Perennials capture water and nutrients 10 or 12 feet down in the soil, 11 months of the year," Glover says. The deep roots and ground cover would also hold on to fertilizer—reducing the cost to the farmer as well as to the environment.

  The perennial wheat-wheatgrass hybrid now growing at the Land Institute can already be made into flour. Yields are too low to compete with annual wheat in Kansas—but maybe not in Nepal, which has steeper slopes and a harsher climate, and where a researcher is now testing perennial hybrids in small plots. Amber waves of perennial grain may be decades away, but the emergence of cheap DNA sequencing is allowing plant breeders to work much faster than they used to. Buckler thinks that for a tiny fraction of the billions spent annually on corn research, one could create field-testable perennial corn in as little as ten years. "I think we should take a shot at revolutionizing agriculture," he says.

  第五篇科學類文章,人們常年以來一直用的是單年生的農作物來種莊稼,現在科學家想要發展多年生植物。這個話題在去年也出現過很多次,關于糧食安全和農業的話題,也是現在科學類文章當中會經常出現的話題。

  閱讀題目分析:

  閱讀的題目部分,加強了對主旨題的考查,尤其是全文的主旨題,幾乎每一篇都出現了這篇文章的 primary purpose、main focus等題型,所以文章和段落的主旨仍然是一個重點。

  非聯動題的尋證題也出現了,也就是給好了結論讓尋找證據,這就意味著文章當中多出了沒有行數範圍的細節題,所以一些細節題和推理題需要沒有行數提示的情況下自己尋找,對文章的結構要求比較高。

  詞彙題非常典型,沒有出現很難的單詞,基本都是簡單但是有多個含義的單詞,要求找出單詞在原文當中的意思。考到的詞彙有:style(動詞) 、general、steep、bulk、natural。

  相關推薦:

  17年1月21日亞太SAT閱讀原文第四篇

  17年1月21日亞太SAT閱讀原文第三篇

  17年1月21日亞太SAT閱讀原文第二篇

  17年1月21日亞太SAT閱讀原文第一篇



本文關鍵字:2017年1月21日亞太SAT閱讀原文,SAT科學類文章,SAT備考
編輯: qian
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