Dr. Ken Olson shared the following press release with me this weekend. He is presenting at the National No-Till Conference in Cincinnati, OH January 14 -17. This conference is one of the best farmer oriented conferences I have been to.
To claim soil organic carbon is truly being sequestered, Ken Olson says, management practices, such as no-till and cover crops must cause an increase in net soil organic carbon from a previous pre-treatment baseline, as well result in a net reduction in atmospheric carbon dioxide levels.
To claim soil organic carbon is truly being sequestered, Ken Olson says, management practices, such as no-till and cover crops must cause an increase in net soil organic carbon from a previous pre-treatment baseline, as well result in a net reduction in atmospheric carbon dioxide levels.
Olson’s proposed definition of
soil organic sequestration is, “The
process of transferring carbon dioxide from the atmosphere into the soil of a
land unit through plants, plant residues, and other organic solids, which are
stored or retained in the unit as part of the soil organic matter (humus).”
If deeper
soil layers in no-till systems without cover crops are giving back more soil
organic carbon than is being sequestered, farmers may wonder what can be done to
put more carbon back into the soil and keep it there.
Olson
recently completed a 12-year tillage study at the Dixon Springs Agricultural
Research Center in southern Illinois on the effects of cover crops on soil organic
carbon sequestration, storage, retention and loss in corn and soybean fields.
The research was conducted
beginning in 2001 and involved a moderately eroded phase of Grantsburg silt-loam
soil on 5-7% slopes with an average depth of 30 inches to a root-restricting fragipan
(dense, brittle and compact layer).
Olson evaluated plots with no-till,
chisel plow and moldboard plow treatments with and without hairy vetch and
cereal rye cover crops, with the plots situated on moderately well drained,
eroded soil.
A
pre-treatment soil organic carbon stock baseline for the rooting zone (0 to 30 inches)
was used to validate the finding that cover crops sequestered soil organic
carbon in the topsoil, subsoil and root zone of the tillage treatments.
The
sample layers were combined to represent the topsoil (0 to 6 inches) the
subsoil (6 to 30 inches) and the root zone (0 to 30 inches). The sampling depth
was limited due to the presence of a root restricting fragipan at a 30-inch depth.
By 2012,
Olson found the cover-crop treatments had more soil organic carbon stock than those
without cover crops for the same soil layer and tillage treatment. The no-tilled,
chisel plowed and moldboard-plowed plots all sequestered soil organic carbon above
pre-treatment soil organic carbon stock levels with cover crops added.
Here’s a summary of what
Olson’s cover-crop experiment found:
• By June 2012, the
cover-crop effect for no-till resulted in the soil organic carbon stock being
greater in all three soil layers compared to no-till plots without cover crops.
For the no-tilled plots with cover crops, the soil organic carbon stocks were
higher — 61.1 metric tons vs. 47 metric tons after 12 years of cover crops — than
prior to experiment’s beginning. “This suggests that soil organic carbon stock
losses from water erosion and some disturbance or mixing during no-till
planting, aeration, nitrogen injection in corn years, and mineralization were
less than the soil organic carbon gain from the cover-crop treatment,” Olson
says.
• For the chisel and
moldboard-plowed plots, cover crops helped reduce the rate of soil organic
carbon stock loss due to tillage associated with corn and soybean production
and soil erosion, and was able to maintain the 2000 baseline soil organic
carbon stock levels measured before the cover-crop treatments were applied.
• With the addition of cover crops to all
treatments for 12-years, the soil organic carbon stock gains were 30%, 10%, and
18% respectively.
• The 20-year cover-crop
treatment for each tillage system did sequester soil organic carbon resulted in
gains for the no-tilled, chisel plowed and moldboard plowed systems of +1.21, +0.35
and +0.55 metric tons of carbon per hectare per year, respectively.
“The no-till system, with
cover crops, sequestered the most soil organic carbon when compared to the
pre-treatment 2000 baseline soil organic carbon stock,” Olson says. Cover crops
reduce soil organic carbon loss from erosion and increase net soil organic
carbon storage above the pre-treatment soil organic carbon stock.
“Long-Term, Effects of CoverCrops on Crop Yields, Soil Organic Carbon Stocks and Sequestration” was
published in Open Journal of Soil Science and was co-authored by Stephen A.
Ebelhar and James M. Lang. Olson is a researcher in the Department of Natural Resources
and Environmental Sciences in the College of Agricultural, Consumer and
Environmental Sciences at the University of Illinois.
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