Olson compared two decades of data from previously eroded Grantsburg soils on 6 percent slopes to a 30-inch depth with low SOC content in an attempt to quantify the amount and rates of SOC sequestration, storage, retention, or loss as a result of a conversion from conventional tillage to a no-till system. Olson used both the comparison and the pre-treatment SOC measurement methods on the same plot area. His analysis revealed conventional tillage and no-till plot areas had less carbon (C) at the end of the study than at the beginning using the pre-treatment SOC method. According to the comparison method, no-till sequestered 4.1 tons of C per acre for a 17 percent gain during the 20 years of the study. However, the pre-treatment SOC method showed that the no-till plots actually lost 3.1 tons of C per acre, a 13 percent loss in 20 years. Thus, no SOC sequestration had actually occurred during the Dixon Springs study.
There were three major reasons why the comparison study approach was the wrong method for measuring C sequestration on the Dixon Springs plot area. First, the conventional tillage plots were not at steady state and actually lost 30 percent of the C in 20 years due to erosion and SOC-rich sediment being transported off the plots. Second, when the no-till and conventional tillage plots were sampled only once, it was not possible to determine the rate of change over time. Last, the effect of tillage equipment breaking down the soil aggregates increased the carbon available to microbial decomposition and the release of C to the atmosphere as CO₂.
"Field experiments mus
|Contact: Debra Levey Larson|
University of Illinois College of Agricultural, Consumer and Environmental Sciences