Glaser has shown that most of this fertile organic matter comes from black carbonthe organic particles from camp fires and charred wood left over from thousands of years of slash-and-burn farming. The soils, known as Terra Preta, contained up to 70times more black carbon than the surrounding soil, says Glaser.
Unburnt vegetation rots quickly, but black carbon persists in the soil for many centuries. Radiocarbon dating shows that the charred wood in Terra Preta soils is typically more than 1,000 years old.
Slash-and-burn farming can be good for soils provided it doesnt completely burn all the vegetation, and leaves behind charred wood, says Glaser. It can be better than manure . Burning the forest just once can leave behind enough black carbon to keep the soil fertile for thousands of years. And rainforests easily regrow after small-scale clearing. Contrary to the conventional view that human activities damage the environment, Glaser says: Black carbon combined with human wastes is responsible for the richness of Terra Preta soils.Terra Preta soils turn up in large patches all over the Amazon, where they are highly prized by farmers. All the patches fall within 500 square kilometers in the central Amazon. Glaser says the widespread presence of pottery confirms the soils human origins.
为了提高广大考生的阅读理解能力,精选了以下全真模拟题。
The findings add weight to the theory that large areas of the Amazon have recovered so well from past periods of agricultural use that the regrowth has been mistaken by generations of biologists for virgin forest.
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