VOA慢速英语2013 Getting a Firm Grip on Weed Control
时间：2019-01-12 作者：英语课 分类：2013年VOA慢速英语(五)月
Getting a Firm Grip on Weed Control
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 1 qualities outweigh 2 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 3 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 4 or natural treatments like corn gluten can suppress weed growth. Dense 5 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 6 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 for seeds that pass through animals that graze on weeds.
- They are the undesirable elements among the employees.他们是雇员中的不良分子。
- Certain chemicals can induce undesirable changes in the nervous system.有些化学物质能在神经系统中引起不良变化。
- The merits of your plan outweigh the defects.你制定的计划其优点胜过缺点。
- One's merits outweigh one's short-comings.功大于过。
- Objective: To study the acute and chronic toxicity of Ten-flavor-acne eradicating-capsule. 目的：探讨复方中药合剂十味平痤胶囊的急性及慢性毒性。
- We are on the verge of eradicating polio in the world. 我们已在世界消除小儿？痹症的边缘了。
- He remained steadfast in his determination to bring the killers to justice. 他要将杀人凶手绳之以法的决心一直没有动摇。
- They were professional killers who did in John. 杀死约翰的这些人是职业杀手。
- The general ambushed his troops in the dense woods. 将军把部队埋伏在浓密的树林里。
- The path was completely covered by the dense foliage. 小路被树叶厚厚地盖了一层。