2014英语四级听力练习慢速4.6(1)_大学英语听力

2014英语四级听力练习慢速4.6(1)

　　Steven Mirsky, however, notes that some crops may be resisting the treatment.

　　That system works and it works well. But the repeated application ) has the potential to cause resistance. Were certainly seeing resistance on the rise throughout the country.

　　He says cotton growers in the southeastern US have pigweed that resists Roundup.

　　Steven Mirsky and others are studying another possibility: controlling weeds with plants instead of chemical products. In autumn, they cover the ground with what farmers call a cover crop, like rye. Through the spring, they let it grow until reaches a height of nearly two meters. But they do not harvest it. Instead, they roll it flat.

　　We can kill this of crop without using any chemicals. And we can get a nice, sweet suppressive mulch.

　　He separates several centimeters of plant material to get to the cool earth.

　　And by keeping the ground cooler, it also inhibits the germination of weeds.

　　A machine cuts through the protective mat to plant the crop. It grows through the summer.

　　Steven Mirsky says rolling cover crops do more than just fight weeds. The plants pushed down in the spring break up and become rich soil. That means better harvests in the fall.

　　Farmers across the country like the idea. Mr. Mirsky says it could greatly increase production of organic crops grown without the use of herbicides.