Dirt: The Erosion of Civilizations - Kootenay Local Agricultural Society

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Designated the nation’s first conservation demonstration area in 1933, the
Coon Creek basin was severely eroded. Fields plowed in a regular pattern
on even steep slopes lacked cover crops, were inadequately manured, and
had poor crop rotations. Pastures were overgrazed and eroding. Guided over
four decades by the Soil Conservation Service, farmers adopted contour
plowing, included cover crops in crop rotations, increased manure applications,
and plowed crop residues back into the soil. By 1975 widespread adoption
of improved farming practices had reduced hillslope erosion in the
basin to just a quarter of what it had been in 1934.
Recent USDA estimates show soil erosion from U.S. cropland as dropping
from about three billion tons in 1982 to just under two billion tons in
2001, substantial progress to be sure—but still far ahead of soil production.
In the late 1990s Indiana farms still lost a ton of soil to harvest a ton of
grain. Even though we know that the soil conservation efforts of ancient
civilizations proved too little, too late in case after case, we remain on track
to repeat their stories. Only this time we’re doing it on a global scale.
Across the planet, moderate to extreme soil erosion has degraded 1.2 billion
hectares of agricultural land since 1945—an area the size of China and
India combined. One estimate places the amount of agricultural land used
and abandoned in the past fifty years as equal to the amount farmed today.
The United Nations estimates that 38 percent of global cropland has been
seriously degraded since the Second World War. Each year farms around
the world lose 75 billion metric tons of soil. A 1995 review of the global
effects of soil erosion reported the loss of twelve million hectares of arable
land each year to soil erosion and land degradation. This would mean that
the annual loss of arable land is almost 1 percent of the total available.
Clearly this is not sustainable.
Globally, average cropland erosion of ten to a hundred tons per hectare
per year removes soil about ten to a hundred times faster than it forms. So
far in the agricultural era, nearly a third of the world’s potentially farmable
land has been lost to erosion, most of it in the past forty years. In the late
1980s a Dutch-led assessment of global soil erosion found that almost 2 billion
hectares of former agricultural lands could no longer support crops.
That much land could feed billions of people. We are running out of dirt
we cannot afford to lose.
In the mid-1990s David Pimentel’s research group at Cornell University
estimated the economic costs of soil erosion and the potential economic
benefits of soil conservation measures. They considered on-site costs for
dust blow