2. Past: What not to do with dirt

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: NOAA

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 of Congress.

A 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: NASA

This lovely Landsat satellite photo shows south central Iceland, but disguises the country's history of irreversible erosion. Photo: NASA.

Remember 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 for land."

Plumes of dust swarm around houses.

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.

Sepia photo of plow turning the earth.

From Fertile to Fruitless
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.

Ancient statues stand alone on barren plain. When 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 age."

Colorful satellite map of red land bordered by water.

Did the Vikings pillage Iceland?
At the risk of repetition, we offer one last example of good soil biting the dust. When Norwegian Vikings migrated to Iceland 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.

Lesson learned?

There are 1 2 3 4 pages in this feature.
Bibliography | Credits | Feedback | Search