"Farming has destroyed a lot of the rich soil of America's Midwestern prairie. A team of scientists just came up with a staggering new estimate for just how much has disappeared.
The most fertile topsoil is entirely gone from a third of all the land devoted to growing crops across the upper Midwest, the scientists say. Some of their colleagues, however, remain skeptical about the methods that produced this result.
The new study emerged from a simple observation, one that people flying over Midwestern farms can confirm for themselves. The color of bare soil varies, and that variation is related to soil quality.
The soil that's darkest in color is widely known as topsoil. Soil scientists call this layer the 'A-horizon.' It's the 'black, organic, rich soil that's really good for growing crops,' says Evan Thaler, a Ph.D. student at the University of Massachusetts, Amherst."
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