VOA慢速英语 2007 1113a

AGRICULTURE REPORT - Study Points to Risk in Common Method of Enriching Soil
By Jerilyn Watson / Broadcast: Mon, 12 Nov 2007 16:00:00 UTC
This is the VOA Special English Agriculture Report.

For more than half a century, many farmers worldwide have added nitrogen fertilizer to their soil. They do this to increase the supply of organic carbon for the long-term health of the soil.

Corn needs a lot of nitrogen fertilizer

But four scientists from the University of Illinois say too much synthetic¹ nitrogen may instead reduce the organic carbon. They report their findings in the current Journal of Environmental Quality.

The team led by Saeed Khan studied soil taken from the Morrow Plots. These experimental farm fields near the University of Illinois have been used for more than one hundred years.

The researchers studied one area where corn is continuously grown. They compared it with another area where corn is planted in turn with oats and hay.

Over a period of more than fifty years, the area where only corn was grown got more chemical nitrogen fertilizer than the other area. But production in the continuous corn area was twenty percent lower compared to the other area. And the scientists found that both areas had reduced levels of organic carbon.

The researchers also studied field reports from around the world. They say they kept finding evidence of organic carbon reductions for synthetically² fertilized³ soils.

Team member Richard Mulvaney says organic carbon is extremely important for healthy soil. For example, it helps provide air for root growth and increases the soil's ability to store water.

Farmers traditionally made nitrogen with animal waste. They would also plant corn one season and a crop like alfalfa the next season. But many farmers changed their growing methods when synthetic nitrogen became widely available in the nineteen fifties. Before then, the chemical had been used mostly for weapons production for the two world wars.

Corn production and profits rose. But the researchers say over-fertilization often resulted because farmers underestimated the amount of nitrogen already in the soil. Too much fertilization reduces profits and is bad for the environment.

The scientists say they do not question the importance of nitrogen fertilizers for crop production. What their research shows, they say, is the importance of testing the soil before adding them.

Saeed Khan and Richard Mulvaney have created what they call the Illinois Soil Nitrogen Test. Some agriculture experts have praised it. Others, though, have questioned its effectiveness.

And that's the VOA Special English Agriculture Report. This report was written by Jerilyn Watson.

1 synthetic   

adj.合成的，人工的；综合的；n.人工制品

参考例句：

• We felt the salesman's synthetic friendliness.我们感觉到那位销售员的虚情假意。
• It's a synthetic diamond.这是人造钻石。

2 synthetically   

adv. 综合地，合成地

参考例句：

• The time sequence model synthetically reflects trends of groundwater level. 总体来说，季节性时序模型的模拟和预测精度较高。
• You can't do It'synthetically, by just flying around and dropping in. 你不能仅靠坐着飞机到处蜻蜓点水地看看就得出一个综合印象。

3 Fertilized   

v.施肥( fertilize的过去式和过去分词 )

参考例句：

• The study of psychology has recently been widely cross-fertilized by new discoveries in genetics. 心理学研究最近从遗传学的新发现中受益匪浅。
• Flowers are often fertilized by bees as they gather nectar. 花常在蜜蜂采蜜时受粉。