![]() It consists of well-decomposed organic matter called the humus. ![]() She also points out that topsoil may get mixed into underlying soil layers, rather than disappearing completely. The layer below the o-horizon in soil profile is A-horizon, It is also called the topsoil. Michelle Wander, at the University of Illinois, says that the study relies on a series of assumptions to fill in gaps in the data, and those assumptions probably overestimate topsoil loss. Some other soil scientists, however, are skeptical of Thaler's methodology. "I think the USDA is dramatically underestimating the amount of loss," Thaler says. That estimate is far higher than those published by the U.S. student at the University of Massachusetts. This produced their estimate that a third of all cropland in that region had lost its 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. They calculated that about a third of the crops were growing on erosion-prone hills. Thaler's team then expanded their study to fields of corn, soybeans, and other crops within a large area of the upper Midwest that includes much of Indiana, Illinois, Minnesota, and Iowa. The soil gradually fell down hillsides, a little bit each year, as farmers tilled the soil. Thaler believes that a century of plowing is to blame. "The A-horizon was almost always gone on hilltops," he says. What's more, Thaler found that this was consistently the case on particular parts of the landscape. Department of Agriculture has carried out, and found that light brown soil contained so little organic carbon, it really wasn't A-horizon soil at all. Thaler and his colleagues compared that color, as seen from satellites, with direct measurements of soil quality that the U.S. The soil that remains is often much lighter in color. Plowing, though, released much of the trapped carbon, and topsoil was also lost to wind and water erosion. The colour of individual horizons should be defined when the soil is moist, as soon. When settlers first arrived in the Midwest, it was everywhere, created from centuries of accumulated prairie grass. It's full of living microorganisms and decaying plant roots, also called organic carbon. student at the University of Massachusetts, Amherst. 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. The soil that's darkest in color is widely known as topsoil. The color of bare soil varies, and that variation is related to soil quality. The new study emerged from a simple observation, one that people flying over Midwestern farms can confirm for themselves. Some of their colleagues, however, remain skeptical about the methods that produced this result. 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. A team of scientists just came up with a staggering new estimate for just how much has disappeared. Soil on hilltops in this photo is lighter in color, revealing a loss of fertile topsoil.įarming has destroyed a lot of the rich soil of America's Midwestern prairie.
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