1. What's under your feet?
2. Past: What not to do with dirt
3. Present: On thin ground?
4. Future: Dig in
This picture from Stratford, Texas, taken
during the 1935 Dustbowl, vividly shows what can happen when intensively
plowed fields meet a long drought. Photo:
The enduring symbol of conventional (high-yield)
agriculture: the moldboard plow. Overturning surface vegetation
exposes the underlying layer of soil humus and begins decomposing
dead plants on the surface. Such tillage prepares the land for seeds
and bring nutrients to the surface, but over time it can encourage
erosion. Photo: Library
rich, tropical forest once grew on this patch of land on Easter
Island. Depleted soils contributed to the collapse of the societies
that once inhabited the island. Photo:
This lovely Landsat satellite photo shows
south central Iceland, but disguises the country's history of irreversible
erosion. Photo: NASA.
the great Midwest Dustbowl of the 1930s? Us either. But we've seen
the pictures. We can attest: times were hard. Perhaps no account testifies
better than Steinbeck's 1939 novel, The Grapes of Wrath:
"The dispossessed were drawn west- from Kansas,
Oklahoma, Texas, New Mexico; from Nevada and Arkansas, families,
tribes, dusted out, tractored out.... They streamed over the mountains,
hungry and restless - restless as ants, scurrying to find work
to do - to lift, to push, to pull, to pick, to cut - anything,
any burden to bear, for food. The kids are hungry. We got no place
to live. Like ants scurrying for work, for food, and most of all
In previous decades, settlers had discovered
the Great Plains' natural bounty -- fertile soils and mild temperatures.
Expecting the plentiful rain they had known in the eastern U.S.,
farmers plowed the grasslands and planted wheat. Crops grew heartily
until drought set in during the early 1930s. Soon enough, the wheat
refused to grow, and the ground cover that had held the soil in
place was gone. Soil turned to dust, billowing into air, water,
houses and lungs, forcing thousands westward (for a longer account,
see American Agriculture: A Brief History in the bibliography).
The Dustbowl was a product of extreme erosion,
which, says Cornell soil scientist David Pimentel, is still the
most serious conservation issue facing farmers.
"It's one of these insidious problems
that nickel and dimes you to death. One millimeter of soil is
equivalent to 15 tons of soil per hectare," Pimentel says. "If
a farmer has a rainstorm at night that causes sheet erosion, that
farmer won't notice a missing millimeter of soil. But we're talking
about 15 missing tons in a single hectare."
The Dustbowl message is now a management mantra:
An approach that works on one type of land can butcher another.
Take Easter Island. Land that was once lush
forest with fertile soil is now an austere scrap of land
in the Pacific (about 2,000 miles west of South America). What happened
to the islanders who once built the island's famously massive stone
statues has long been a mystery. To solve it, scientists have been
taking a close look at the pollen grains that lie deep in the island's
soils. These grains, together with radiocarbon-dated fossils, says
Jared Diamond, tell of a population that colonized the island, unwittingly
exploited it, and died in a swirl of starvation and cannibalism.
Polynesians settled Easter, around 800AD, they cleared the forests
for gardens and firewood, ate the local land birds, and used the
local palm trees for fruit and rope, says Diamond. By 1600, all
of the trees and land birds were extinct. Without trees to protect
the ground from wind and water, erosion set in. Struggling to survive
on crops, islanders planted and re-planted on small plots of land
until the soil had been drained of nutrients. Having lost the
trees their ancestors used to build sturdy boats, residents were
trapped on barren soil, and the society went out, as Diamond puts
it, in a whimper.
"Easter Island is Earth writ small," Diamond
wrote in 1995 (See "Easter Island's End" in the bibliography). "All
human societies are linked by international transport, and we can
no more escape into space than the Easter Islanders could flee into
the ocean. If we continue to follow our present course, we shall
have exhausted...much of our soil by the time my sons reach my current
At the risk of repetition, we offer one last
example of good soil biting the dust. When Norwegian Vikings migrated
in the 9th century AD, they discovered unfamiliar ground. Norway
has thick, clay soils too heavy to be blown away when bound by vegetation.
Icelandic soils, by contrast, are light and powdery, the product
of ashes blown out in volcanic eruptions.
The Vikings, Diamond explains, cleared the
forests over those soils to create pastures for domestic animals.
Within a few generations, half of the topsoil in Iceland had eroded
into the sea.