Soil scientist John Reganold says，“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.

　　“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.”

　　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.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 (玉米)，millet or sorghum crops.They not only add nitrogen (氮) 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.

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