Dirt: The Erosion of Civilizations - Kootenay Local Agricultural Society

Soil erosion rapidly became a major problem once the loess was cleared
and plowed. In the early 1900s Washington State Agricultural College’s
William Spillman toured the region lecturing on the threat of soil erosion
from the common practice of leaving plowed fields bare each summer. Few
heeded the young professor’s warning that each year’s annoying rills would
eventually add up to a serious problem.
In the 1930s tractors began replacing horse-drawn plows in the Palouse
and elsewhere, allowing a single operator to farm much larger acreages.
Eager to capitalize on the greater labor efficiency, landowners changed the
traditional arrangement for sharecropping on leased land. Instead of keeping
two-thirds of what they grew, tenants were now allowed to keep just
over half. So tenants worked the land that much harder, reducing outlays
for luxuries like erosion control. Farmers were now working more land,
but not necessarily making more money.
By 1950 a USDA survey reported that all of the original topsoil was missing
from 10 percent of Palouse farmland. Between 25 and 75 percent of the
topsoil was missing from an additional 80 percent of the land. Just 10 percent
of the region retained more than 75 percent of its original soil. Annual
surveys of soil loss from 1939 to 1960 showed an average loss of half an inch
a decade. On slopes steeper than about fifteen degrees, soil loss averaged
an inch every five years.
A cistern installed in 1911 on a farm near Thornton dramatically illustrates
the effect of plowing sloping fields. Originally projecting about a
foot and a half above the adjacent hilltop, by 1942 it stuck out nearly four
feet above the surrounding field. By 1959 the same cistern stood six feet
above the field. Four and a half feet of soil had been plowed off the slope
in less than fifty years—about an inch a year. Some eastern Idaho soils that
were more than a foot thick in the early twentieth century were barely deep
enough to plow by the 1960s when just half a foot of soil remained above
bedrock.
From 1939 to 1979 the total erosion on Palouse cropland averaged more
than nine tons per acre per year; and reached more than one hundred tons
per acre per year on steep slopes. Erosion rates on unplowed rangeland and
forested land averaged less than one ton per acre per year. Plowing the loess
increased erosion rates by a factor of ten to a hundred, with most of the
loss caused by erosion from runoff across newly plowed ground. Simple
soil conservation measures could halve erosion without reducing farm
income. But doing so requires fundamental changes in farming practices.
dust blow 161