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Losing Soil |
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http://www.earth-policy.org/Books/Seg/PB2ch05_ss3.htm
Lester R. Brown
In 1938, Walter Lowdermilk, a senior official in the Soil Conservation
Service of the U.S. Department of Agriculture, traveled abroad to look at
lands that had been cultivated for thousands of years, seeking to learn
how these older civilizations had coped with soil erosion. He found that
some had managed their land well, maintaining its fertility over long
stretches of history, and were thriving. Others had failed to do so and
left only remnants of their illustrious pasts.
In a section of his report entitled “The Hundred Dead Cities,” he
described a site in northern Syria, near Aleppo, where ancient buildings
were still standing in stark isolated relief, but they were on bare rock.
During the seventh century, the thriving region had been invaded,
initially by a Persian army and later by nomads out of the Arabian Desert.
In the process, soil and water conservation practices used for centuries
were abandoned. Lowdermilk noted, “Here erosion had done its worst....if
the soils had remained, even though the cities were destroyed and the
populations dispersed, the area might be re-peopled again and the cities
rebuilt, but now that the soils are gone, all is gone.”
Now fast forward to a trip in 2002 by a United Nations team to assess the
food situation in Lesotho, a small country of 2 million people imbedded
within South Africa. Their finding was straightforward: “Agriculture in
Lesotho faces a catastrophic future; crop production is declining and
could cease altogether over large tracts of the country if steps are not
taken to reverse soil erosion, degradation, and the decline in soil
fertility.” Michael Grunwald reports in the Washington Post that nearly
half of the children under five in Lesotho are stunted physically. “Many,”
he says, “are too weak to walk to school.”
Whether the land is in northern Syria, Lesotho, or elsewhere, the health
of the people living on it cannot be separated from the health of the land
itself. A large share of the world’s 852 million hungry people live on
land with soils worn thin by erosion.
The thin layer of topsoil that covers the planet’s land surface is the
foundation of civilization. This soil, measured in inches over much of the
earth, was formed over long stretches of geological time as new soil
formation exceeded the natural rate of erosion. As soil accumulated over
the eons, it provided a medium in which plants could grow. In turn, plants
protect the soil from erosion. Human activity is disrupting this
relationship.
Sometime within the last century, soil erosion began to exceed new soil
formation in large areas. Perhaps a third or more of all cropland is
losing topsoil faster than new soil is forming, thereby reducing the
land’s inherent productivity. Today the foundation of civilization is
crumbling. The seeds of collapse of some early civilizations, such as the
Mayans, may have originated in soil erosion that undermined the food
supply.
The accelerating soil erosion over the last century can be seen in the
dust bowls that form as vegetation is destroyed and wind erosion soars out
of control. Among those that stand out are the Dust Bowl in the U.S. Great
Plains during the 1930s, the dust bowls in the Soviet Virgin Lands in the
1960s, the huge one that is forming today in northwest China, and the one
taking shape in the Sahelian region of Africa. Each of these is associated
with a familiar pattern of overgrazing, deforestation, and agricultural
expansion onto marginal land, followed by retrenchment as the soil begins
to disappear.
Twentieth-century population growth pushed agriculture onto highly
vulnerable land in many countries. The overplowing of the U.S. Great
Plains during the late nineteenth and early twentieth centuries, for
example, led to the 1930s Dust Bowl. This was a tragic era in U.S.
history, one that forced hundreds of thousands of farm families to leave
the Great Plains. Many migrated to California in search of a new life, a
move immortalized in John Steinbeck’s "The Grapes of Wrath."
Three decades later, history repeated itself in the Soviet Union. The
Virgin Lands Project between 1954 and 1960 centered on plowing an area of
grassland for wheat that was larger than the wheatland in Canada and
Australia combined. Initially this resulted in an impressive expansion in
Soviet grain production, but the success was short-lived as a dust bowl
developed there as well.
Kazakhstan, at the center of this Virgin Lands Project, saw its grainland
area peak at just over 25 million hectares (44 millions acres) around
1980, then shrink to 14 million hectares today. Even on the remaining
land, however, the average wheat yield is scarcely 1 ton per hectare, a
far cry from the nearly 8 tons per hectare that farmers get in France,
Western Europe’s leading wheat producer.
A similar situation exists in Mongolia, where over the last 20 years half
the wheatland has been abandoned and wheat yields have also fallen by
half, shrinking the harvest by three fourths. Mongolia--a country almost
three times the size of France with a population of 2.6 million--is now
forced to import nearly 60 percent of its wheat.
Dust storms originating in the new dust bowls are now faithfully recorded
in satellite images. In early January 2005, the National Aeronautics and
Space Administration (NASA) released images of a vast dust storm moving
westward out of central Africa. This vast cloud of tan-colored dust
stretched over some 5,300 kilometers (roughly 3,300 miles). NASA noted
that if the storm were relocated to the United States, it would cover the
country and extend into the oceans on both coasts.
Andrew Goudie, Professor of Geography at Oxford University, reports that
Saharan dust storms--once rare--are now commonplace. He estimates they
have increased 10-fold during the last half-century. Among the countries
in the region most affected by topsoil loss from wind erosion are Niger,
Chad, Mauritania, northern Nigeria, and Burkino Faso. In Mauritania, in
Africa’s far west, the number of dust storms jumped from 2 a year in the
early 1960s to 80 a year today.
The Bodélé Depression in Chad is the source of an estimated 1.3 billion
tons of wind-borne soil a year, up 10-fold from 1947 when measurements
began. The 2 to 3 billion tons of fine soil particles that leave Africa
each year in dust storms are slowly draining the continent of its
fertility and, hence, its biological productivity. In addition, dust
storms leaving Africa travel westward across the Atlantic, depositing so
much dust in the Caribbean that they cloud the water and damage coral
reefs there.
In China, plowing excesses became common in several provinces as
agriculture pushed northward and westward into the pastoral zone between
1987 and 1996. In Inner Mongolia (Nei Monggol), for example, the
cultivated area increased by 1.1 million hectares, or 22 percent, during
this period. Other provinces that expanded their cultivated area by 3
percent or more during this nine-year span include Heilongjiang, Hunan,
Tibet (Xizang), Qinghai, and Xinjiang. Severe wind erosion of soil on this
newly plowed land made it clear that its only sustainable use was
controlled grazing. As a result, Chinese agriculture is now engaged in a
strategic withdrawal in these provinces, pulling back to land that can
sustain crop production.
Water erosion also takes a toll on soils. This can be seen in the silting
of reservoirs and in muddy, silt-laden rivers flowing into the sea.
Pakistan’s two large reservoirs, Mangla and Tarbela, which store Indus
River water for the country’s vast irrigation network, are losing roughly
1 percent of their storage capacity each year as they fill with silt from
deforested watersheds.
Ethiopia, a mountainous country with highly erodible soils on steeply
sloping land, is losing an estimated 1 billion tons of topsoil a year,
washed away by rain. This is one reason Ethiopia always seems to be on the
verge of famine, never able to accumulate enough grain reserves to provide
a meaningful measure of food security.
Fortunately there are ways to conserve and rebuild soils. These will be
discussed in the next Earth Policy Institute Book Byte.
# # #
Adapted from Chapter 5, “Natural Systems Under Stress,” in Lester R.
Brown, Plan B 2.0: Rescuing a Planet Under Stress and a Civilization in
Trouble (New York: W.W. Norton & Company, 2006), available on-line at
www.earthpolicy.org/Books/PB2/index.htm
Additional data and information sources at www.earthpolicy.org
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