Monday, November 5, 2007
99-9
Carbon Turnover of Corn Root Residue Among Agricultural Management Systems in the Upper Midwest.
The turnover of carbon in agro-ecosystems is strongly influenced by climate, agricultural management, and edaphic variation among sites, and understanding these controls on soil carbon cycling is key to modeling ecosystem carbon balance. The contribution of root residue to stable soil organic carbon (SOC) pools is thought to be greater than that of shoot residue. However, root contributions are rarely estimated in studies comparing the long term effects of agricultural management on SOC due to the inherent difficulty in tracking belowground processes. We used stable carbon isotopes to track the fate of recent corn root residue in a set of five management systems common to the upper Midwest . The management systems in our study vary in crop rotation, tillage, and fertilization, and have been managed consistently since 1989 allowing for a long term record of management effects to accumulate. We determined the percent of total soil respiration originating from recent residue via repeated measurements of 13C-CO2 and total CO2 losses using static chambers. Early growing season measurements show that recent root residue accounts for 12 to 16% of the total CO2 flux across management systems, while end of the season measurements show 6 to 9% of the flux coming from recent root residue. Differences among management systems in the fraction of soil respiration originating from root residue for each sampling date are not significant overall. The results suggest that, within a growing season, management effects on the turnover rate of carbon from root residue are minimal.
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