Seattle, Washington
August 8, 2007
University
of Washington Traditional plow-based agricultural
methods and the need to feed a rapidly growing world population
are combining to deplete the Earth's soil supply, a new study
confirms.
In fact, long-established
practices appear to increase soil erosion to the point that it
is not offset by soil creation, said
David Montgomery, a
University of Washington
professor of Earth and space sciences.
No-till agriculture, in which
crop stubble is mixed with the top layer of soil using a method
called disking, is far more sustainable, he said.
"Soil loss through conventional
agriculture is in a range of 10 to 100 times greater than the
rate at which soil is created. No-till agriculture brings it
into the ballpark, surprisingly close to being balanced with
soil creation," he said.
Montgomery looked at data from
more than 1,650 measurements published in more than 200 studies
examining various aspects of farming practices, soil creation
and erosion. His findings are being published this week in the
online edition of the Proceedings of the National Academy of
Sciences, and will be published in a print edition later in the
year.
Long-term erosion rates
worldwide average less than one-tenth of a millimeter per year,
which is similar to the rate at which soil is produced through
mechanical, chemical and biological processes that dissolve rock
and mix the grains with organic matter. The research shows that
erosion rates consistently exceed 1 millimeter a year – less
than a half-inch per decade – only in steep alpine terrain, and
plowed fields erode at about the same pace as the Himalayas,
home to the highest mountain peaks in the world.
The paper supports arguments
Montgomery put forth in a popular book, "Dirt: The Erosion of
Civilizations," published earlier this year by the University of
California Press. In the book, he linked the demise of history's
major civilizations to how long it took them to deplete their
soil supply.
In the case of civilizations
past, when the soil wore out the people could move to other
places and find rich enough soil to sustain them. But with the
world population now exceeding 6.6 billion people, Montgomery
argues that there are few, if any, places left where the soil
can feed a large population for very long.
"We are skinning our
agricultural fields," Montgomery said. "But there are methods of
farming, no-till in particular, that don't have to lead to that
result."
No-till agriculture does away
with plowing, which often involves stripping crop stubble from
fields before deeply turning the soil. Often a plowed field will
be disked to remove stubble and weeds. No-till agriculture uses
disking to turn only the top layer of soil. Some other methods,
such as hand-tilling on terraced fields, also preserve the soil
but are more labor intensive and so are not practical on a large
scale, Montgomery said.
He noted that as oil becomes
more expensive and less available, it will be even more
important to preserve soil fertility through methods such as
no-till farming, which requires less fertilizer and many fewer
passes with a tractor.
No-till farming can build soil
fertility even with intensive farming methods, he said, and it
could prove to be a major benefit in a warming climate. By
stirring crop residue into the soil surface, no-till farming can
gradually increase organic matter in soil, as much as tripling
its carbon content in less than 15 years.
"Returning the organic matter
to the soil stores carbon," Montgomery said. "If all farms on
the planet were converted to no-till, the range of estimates for
sequestered carbon runs from 10 percent of current carbon
emissions to about half.
"It's probably closer to 10
percent, but even that would be a significant benefit," he said.
"It's one of the few win-win options in trying to forestall the
effects of climate change." |
