(单词翻译:单击)
听力文本
This is the VOA Special English Agriculture Report.
When is a plant considered a weed? Experts at Penn State University have a simple answer: When the undesirable qualities outweigh the good qualities.
Consider the fact that crops generally produce several hundred seeds from each plant. By comparison, each weed plant can produce tens or even hundreds of thousands of seeds. And some buried seeds can survive up to forty years -- or even longer.
Eradicating weeds means that you have to remove all the seeds and roots so the plants will not grow back. But birds or the wind can reintroduce them to the land.
A more common way to deal with weeds is to control them enough so that the land can be used for planting. Experts advise using two or more control methods to deal with weeds.
Chemical weed killers or natural treatments like corn gluten can suppress weed growth. Dense planting of a crop can also act as a natural control.
Bill Curran is a professor of weed science at Penn State in University Park, Pennsylvania. He says one of the most common methods for suppressing weeds is dense planting.
He says a dense, competitive crop that quickly shades the soil will help suppress many weeds. The seeds need light to grow, so blocking the sun will reduce weed growth.
Other controls include turning over the soil, pulling the weeds or covering them with mulch made of shredded wood, garden waste or other material.
But even mulch has its limits. Natural resource specialists point out that weeds can be transported in mulch. This is also true of soil, grain, hay and animals.
Yet animals like sheep or goats eat weeds, so they can provide a biological control. Insects and other organisms can also act as biological controls.
Preventing the spread of weeds is an important part of weed management. Farm vehicles should be kept out of areas with weeds. If that is not possible, then clean off the equipment and your shoes when leaving.
Some people burn weeds or bury them deeply or make them into mulch.
Professor Curran says another way to make use of weeds is to compost them. Heat is produced in the process of making organically rich compost to improve soil. The heat will kill many, though not all, weed seeds. The same is true of seeds that pass through animals that graze on weeds.
And that's the Agriculture Report, written by Jerilyn Watson. You can also find caption and videos at the VOA Learning English channel on YouTube. I'm Jim Tedder.
文本来自51voa，译文属可可原创，仅供学习交流使用，未经许可请勿转载。
词汇解释
1.outweigh vt. 比…重（在重量上）；比…重要；比…有价值
The gain is outweighed by the loss.
得不偿失。
2.suppress vt. 抑制；镇压；废止
Any kind of assembly was suppressed in this country.
该国过去禁止一切形式的集会。
3.mulch n. 覆盖物，护盖物；护根 vt. 做护根；以护盖物覆盖
In May, mulch the bed with garden compost.
五月，在苗床上盖些肥料。
内容解析
1.Other controls include turning over the soil, pulling the weeds or covering them with mulch made of shredded wood, garden waste or other material.
turn over 移交给；翻阅；把…翻过来；发动；营业额达到；反复考虑
The doctor turned the patient over and looked at his back.
医生给病人翻了个身，检查他的背部。
The demonstrator turned over a police car.
示威者推翻了一辆警车。
参考译文
这里是美国之音慢速英语农业报道。
植物在什么时候被当做杂草？宾夕法尼亚州立大学的专家们给了简单的答案，那就是当不合意的品质大于良好品质时。
考虑到每棵作物通常产出几百粒种子，相比之下，每棵杂草可以产出数万或数十万种子。一些被埋藏地下的种子可以存活四十年甚更久。
除去杂草意味着将所有种子和根都除掉，这样就不会再生。但鸟和风能把种子再度带回土地。
更常见的除草办法就是将草控制到一定程度，这样土地可以种植作物。专家建议使用两种或多种办法来对付杂草。
化学杀虫剂或玉米黄粉等自然方法可抑制杂草生长，将作物种稠密些也可自然控制杂草。
Bill Curran是宾夕法尼亚州立大学大学城分校教授，他说最常见的控制杂草的办法是密植。
他说，稠密、竞争性强的作物可以快速遮盖土壤并抑制多种杂草，种子生长需要阳光，所以封锁阳光就阻止杂草的生长。
其他的控制办法包括翻地，拔出杂草或用地膜覆盖，地膜是由碎木屑、花园废料等材料制成。
但甚至地膜也有局限性，自然资源专家指出，杂草可以在地膜中蔓延，也可在土壤、谷物、甘草和动物间传播。
但绵羊、山羊等动物吃草，所以它们可以进行生物控制。害虫等生物也可进行生物控制。
控制杂草蔓延是杂草管理的重要部分，农机应远离杂草区，如果无法做到，应在离开时清理设备和鞋子。
也有人燃烧杂草或将之深埋或将之制成地膜。
Curran教授说，还有办法就是将杂草做成肥料。制作有机堆肥以改良土壤的过程中会产生热量，这些热量会杀死大部分杂草，将杂草喂食动物将之消化的过程也是如此。
这就是美国之音慢速英语农业报道，作者杰瑞琳·沃森，你可在YouTube美国之音英语学习频道获得字幕和视频，我是吉姆·泰德。
