This is the VOA Special English Agriculture Reportt, from
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Organic
farming avoids the use of chemical pesticides and manmade fertilizers.
Supporters say organic farming is better for the environment than other methods.
But studies have shown that organic farming often produces less food per
hectare. That lower yield means feeding the world organically would require more
land. But good farmland is limited. And scientists say deforestation from the
clearing of land for agriculture is already a problem for climate change. In a
new study, researchers wanted to measure the difference between conventional and
organic yields. So they combined the results of sixty-six earlier studies. They
found that some organic farms can yield almost as much as conventional farms.
But most cannot. The findings were reported in the journal Nature. The study's
lead author was Verena Seufert of McGill University in Canada. She says
convention farms usually have higher yields than organic ones. But some
activities, environmental conditions and even crops can narrow the differences.
On average, organic farms produced twenty-five percent less compared to
conventional farms. But yields of organic fruits and other perennial crops
nearly equaled the yields from conventional ones. So did the yields of legumes
such as soybeans. Legumes produce some of their own nitrogen fertilizer.
However, organic vegetables and cereal crops had a lot lower yields compared to
conventionally grown crops. Ms. Seufert says the soil on organic farms holds
water better, and that can reduce the yield difference. Also, organic farmers
can improve their yields by making sure crops get enough fertilizer. But
increasing the nitrogen is harder to do organically, using just animal waste and
crop rotations. Organic farmers rotate food crops with plants that fertilize the
soil. But while these "cover," or fertilizer, crops are growing, food crops have
to be grown on other land. And if farmers use manure, they have to feed the
animals that produce it, and that requires grazing land or crop land. The United
Nations says world demand for food will grow seventy percent by the middle of
the century. John Reganold is a scientist at Washington State University. He
says no one should dismiss organic agriculture as part of the solution. He says
farming is increasingly a mix of organic and conventional methods. For VOA
Special English, I'm Alex Villarreal.(Adapted from a radio program broadcast
01May2012)
원문출처 : http://www.youtube.com/watch?v=XYY-pp0cFbQ&feature=youtube_gdata
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