Chương trình học tiếng Anh của VOA: Special English Agriculture Report - Controlling Weeds. Xin hãy vào http://www.youtube.com/user/VietSpecialEnglish để xem các bài kế tiếp.
This is the VOA Special English Agriculture Report.
Weeds compete with plantings for water and nutrients. So farmers and gardeners may have good reason to hate them. But weeds can also bring pretty flowers and wild beauty to places lacking either. British nature writer Richard Mabey offers support for them in his new book. The title says it all. "Weeds: In Defense of Nature's Most Unloved Plants."
But when exactly is a plant considered a weed? Experts at Penn State University say the answer is simple: when the undesirable qualities outweigh the good qualities.
A crop plant generally produces several hundred seeds. But a weed plant can produce tens or even hundreds of thousands of seeds. And if seeds get buried, they may survive for many years underground.
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. But so can dense planting. Bill Curran is a professor of weed science at Penn State. He says a dense, competitive crop that quickly shades the soil from the sun will help reduce weed growth.
Other controls include turning over the soil, pulling the weeds or covering them with mulch made of 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 deep in the ground or make them into mulch.
Professor Curran says another way to make use of weeds is to compost them. The process of making organically rich compost produces heat. This heat kills many, though not all, weed seeds. The same is true for seeds that pass through animals that graze on weeds.