Agroecosystems / Carbon Sequestration Research Focus |
Iowa Final Report
Executive Summary Land managers have long known the importance of soil organic matter in maintaining the productivity and sustainability of agricultural land. More recently, interest has developed in the potential for using agricultural soils to sequester C and mitigate increasing atmospheric carbon-dioxide by adopting practices that increase standing stocks of carbon in soil organic matter and vegetation. Practices that increase the amount of CO2 taken up by plants (through photosynthesis), which then enter the soil as plant residues, tend to increase soil C stocks. Likewise, management practices that reduce the rate of decay or “turnover” of organic matter in soils will also tend to increase carbon stocks. In 1997, we initiated a state-wide assessment of how management decisions involving cropping and tillage systems affect soil organic matter. Our approach utilized a variety of resource data (on climate, soils, land use and management), long-term field experiment results, and the Century EcoSystem Soil Organic Matter Computer Model (Parton, et al., 1987, 1994; Metherall, et al., 1993). An initial The Phase II study was started in 1998 and involved all 99 counties. This approach of involving every county within a state had never been attempted for assessing the impacts of management on soil carbon. For the project to be successful, it was necessary to devise a means of improving communication with the local land managers and collecting the local data. A survey instrument, called the Carbon Sequestration Rural Appraisal (CSRA), was designed, tested and then implemented in each county. This local data provided additional inputs into the Century Model that were not available in previously published databases, and refined the output for the individual counties and the soils and crop/tillage systems within each county. Century estimates for 203,000 different scenarios showing the C changes are now available in an Access database. The county summaries for the amounts of C sequestered in 1998 are also available. The Phase II assessment for Iowa suggests that agricultural soils are currently (based on 1998 data) sequestering 3.1 MMT of carbon per year (equivalent to 11 MMT of CO2 per year), largely through increased adoption of conservation practices over the past 10 to 20 years. This amount is equivalent to an offset of 16.7% of Iowa’s fossil fuel carbon emissions, based on 1997 emission estimates of 18.5 MMT C per year (EPA, 2001). |