Soil organic carbon (SOC) sequestration has yet again become a topic of heated debates, as University of Illinois professor of soil science Kenneth Olson, is about to release a detailed study on the influence of tillage practices on atmospheric carbon sequestration in the upcoming issue of the journal Geoderma.
The professor gathered data from over 20-year period at Dixon Springs and developed a protocol for more accurate measurements of removed carbon from the atmosphere.
He stated that past experiments have showed that no-till on soil preserves the stored carbon in soils. However this does not necessary mean that it helps carbon sequestration, it simply lowers down the rate of release.
To reach to this conclusion, Olson conducted a pre-treatment SOC measurement method to compare changes in soil organic carbon over time. He evaluated the commonly used comparison method, and outlined its main limitation- it is based on the assumption that the conventional tillage baseline is at a steady state and having the same amount of SOC at the beginning and at the end of the long-term study. But this is not always true. In order to determine whether sequestration has occurred, the no-till should be compared to itself on the same soil, but at different times.
Olson quantified the amounts and rates of soil organic carbon sequestration, storage, retention, or loss caused by conventional tillage and no-till system, using 20 years of data on Grantsburg soils.
He applied both methods to establish that, firstly the comparison study approach gives misleading estimates and secondly that for the period of the two decades no SOC sequestration has occurred.
The certainty of his findings comes from the fact that the conventional tillage plots were not a steady state and soil erosion transported sediments off them. In addition, all plots were sampled only once, not allowing temporal estimation of change. Lastly, as a result from breaking down of soil aggregates through tillage, increased microbial decomposition increased the release of C to the atmosphere.
Olson concluded that future experiments should be designed more precisely, with more accurate calculations and refined field and laboratory methods. He also suggested improvements and clarifications of current definitions of SOC sequestration. He is certain that carbon, which is not directly from the atmosphere and from outside the land unit should not be considered as sequestered.
He proposed protocols that are needed so that science can move forward. In his opinion, future Cap and Trade programs should include establishing of protocols for measuring SOC sequestration, so that landowners can prove their claimed net carbon gains and the permanent storage in their soils.