200780721.jpg

Sloan/USDA, 1936

Buried.
Drought and overplowing in the 1930s resulted in dust storms that covered farm machinery.

The Dirty Truth About Plowing

2007-08-07 (All day)
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Each year, 24 billion tons of the world's soil blows or washes away, largely because of plowing. Now, the first large-scale analysis of an alternative farming method that eschews the plow confirms that it stems soil loss.

As plows tear into the ground, they loosen the upper 6 to 8 inches (15 to 20 cm) of soil, exposing the dirt to rain and wind. Mechanized plows introduced in the 1930s have accelerated the loss, leading conservationists to explore no-till agriculture. This method leaves fields unturned and allows crop stubble to remain on the surface to protect the soil; farmers plant new crops by making small holes in the layer of plant material. Although this method involves more work, case studies have indicated that no-till farming greatly reduces erosion. But so far, research has been limited to small clusters of farms.

To find out whether no-till farming prevents soil loss on a larger scale, geologist David Montgomery of the University of Washington, Seattle, scoured agricultural studies dating back to the early 1940s for erosion data. After gathering 1673 measurements from areas as far apart as the Himalayas and the U.S. Midwest, he compared no-till erosion losses to those from farms that practice conventional agriculture.

As Montgomery reports online this week in the Proceedings of the National Academy of Sciences, plowless farms lost an average of 0.082 mm of soil each year, an erosion rate close to the natural geologic rate of 0.03 mm per year. Annual soil loss on plow-based farms, by contrast, averaged 1.5 mm of erosion--almost 20 times as much. On average, conventional farms lost soil about 90 times faster than new soil is produced. The findings are the first to show that no-plow methods reduce erosion to almost natural, geologic rates, says Montgomery.

Steve Kaffka, a crop scientist at the University of California, Davis, agrees. Still, he notes, no-till farming can lead to increased weed growth, which conventional farmers may attempt to combat with herbicides. Although organic methods are available to combat weeds, the overall sustainability of no-till farming can't be determined unless researchers examine the environmental harms of toxic substances commonly used on no-till farms, he says.

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