Cover Crops Can Sequester Soil Organic Carbon

 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.

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.