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(Cheryl Carlin)

Giant Footprint

How the world's 6.6 billion people threaten the health of the ecosystem

"This means we could strip off topsoil in a couple hundred to a couple thousand years," says Montgomery . "The current rate of erosion is one that should worry civilization over the next couple of centuries, but the problem plays out so slowly it's hard for people to wrap their heads around it."

To counter the problem, Montgomery advocates wide-scale adoption of no-till agriculture. That approach forgoes the use of a plow to turn the soil, which leaves topsoil more susceptible to erosion; instead, farmers lightly churn crop stubble into the topsoil. Although no-till farming may require the use of pesticides and herbicides under some conditions, this would be outweighed over the long term by a number of benefits, says Montgomery. No-till farming, he asserts, would reduce erosion to rates closer to that of natural soil production. Other benefits include improved soil fertility and increased carbon storage as more organic matter accumulates in the soil.

For years, scientists have widely assumed that massive soil erosion from agriculture plays a significant role in altered levels of carbon in the atmosphere. Yet the exact nature of that link isn't well understood, and evidence from various studies has been highly contradictory. Some studies have concluded that global soil erosion from agriculture releases considerable amounts of carbon into the atmosphere; others found a sizable carbon "sink" effect.

An October report in Science refutes both those claims. Using a new method of analysis, an international team of scientists headed by Kristof Van Oost of Catholic University of Leuven in Belgium found that global agricultural soil erosion has a minimal effect on levels of atmospheric carbon. It does captures carbon, these researchers say, but only a fragment, in amounts well below some previous estimates.

Diana Parsell of Falls Church, Va., writes often on topics in science.

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