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This is the VOA Special English Agriculture Report.

Studies show farmland in Africa is often lacking in important nutrients. But researchers say a combination of farming methods may help.

Since the world food crisis several years ago, researchers have directed more of their attention to small farms. Most farms in areas south of the Sahara Desert are only about one or two hectares. One of the goals is to increase production without necessarily clearing more land to grow additional crops.

American researchers say that can happen with greater use of an agricultural system called perenniation. It mixes food crops with trees and perennial plants – those that return year after year.

Soil scientist John Reganold is with Washington State University.

JOHN REGANOLD: “One of the major problems (is that the) soils are fairly poor in most of the regions. So how do you grow food on poor soils? There have to be food production systems that can build the soil and improve the yield.”

Mr. Reganold says poor soil may have resulted from years of weathering that washed away many nutrients. He says some farmers may have done more harm than good.

JOHN REGANOLD: “They have been actually using farming practices where they’re not putting in organic matter. They’re not putting in fertilizers. They can’t afford those things. And it just runs the soil down. So they’re worsening the situation.”

He estimates that up to two billion dollars worth of nitrogen, phosphorous and potassium is lost from African soil each year.

The scientist says the word perenniation defines three systems that are already used in Africa. The oldest of the three is called evergreen agriculture. This is where farmers plant trees with their crops. John Reganold says farmers in Africa have been doing this for sixty years, but it seems to be growing in popularity.

The method is gaining widespread use in countries such as Niger, Burkina Faso, Malawi and Zambia. The trees are planted among maize, millet or sorghum crops. They not only add nitrogen to the soil through their roots, but also through their leaves when they fall off and break down. At other times of the year, the trees can protect plants from strong sunlight.

John Reganold says he knows of one woman who has had great success with perenniation.

JOHN REGANOLD: “She’s a grandmother in her fifties. Her name is Rhoda Mang’yana and she started using this system about twenty years ago. And her yields initially were about a ton of maize. Now with a good year she gets four tons per hectare. Four times what she was getting.”

Mr. Reganold was one of three researchers who wrote a report about perenniation. It was published in the journal Nature.

And that’s the VOA Special English Agriculture Report. I’m Steve Ember.

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（来源：VOA 编辑：Julie）