Soil scientist Lloyd Owens collects a water sample
for carbon analysis. Click the image for more information about
it.
Read the
magazine
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A One-Time
Plowing May Not Hurt Carbon Credits
By Don Comis
October 13, 2004 A one-time tillage will not cause
great soil carbon loss, even though major damage is caused to soil structure.
That's the finding of Lloyd Owens, a soil scientist with the
Agricultural Research Service in
Coshocton, Ohio, after a study comparing soil carbon in the top foot of soil
under a meadow with the carbon level in soil under cornfields with various
levels of tillage. He found that it takes a few years of continual annual
plowing before carbon losses become noticeable in fields previously unplowed
for years.
Sometimes farmers plow land that is removed from a federal conservation
reserve program. Such programs pay farmers to protect land with a
"permanent" vegetative cover such as grass, usually for 10 years at a
time. Another reason why farmers in the northern Midwest might plow is to help
control a heavy infestation of slugs.
It was just such a slug infestation that inspired Owens to study the effects
of plowing on soil carbon. He found that for the first year of plowing land,
the upper eight inches--the plow layer--held about 19 tons of carbon per acre,
the same as was retained in the meadow and untilled cornfields. But after a few
years of annual plowing, the loss became noticeable, and, by the fifth year,
the soil carbon level fell to 15 tons an acre.
Although there was no noticeable loss of stored soil carbon in the first
year of plowing, there were other trade-offs. That's because just one pass with
a plow greatly damages soil structure, which increases erosion and reduces
water infiltration and soil health. Also, a single plowing moves more than half
the organic matter in a field a little deeper underground, away from the
surface where it is needed to hold water and nutrients.
Read
more about this research in the October 2004 issue of Agricultural
Research magazine.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.
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