Soil carbon (C) management is a key issue in many sustainable agriculture programs and global climate change studies. However, efforts to determine the best management practices for carbon sequestration are complicated by the inherent variability of soil properties. Among the factors influencing magnitude and direction of long-term management effects are soil C levels prior to management implementation. In this study we tested the hypothesis that carbon sequestration rates are higher in soils with low initial C levels than in soils with high initial C level. We studied three management systems, namely, chisel plow and no-till with conventional chemical inputs, and a certified organic chisel plowed system with a winter leguminous cover crop and no compost or manure inputs at the Long Term Ecological Research site in SouthWest Michigan established in 1988. In 2003-2004 we collected approximately 100 soil samples at 0-5 cm depth for total soil C measurements from each of the 18 1-ha experimental plots. Initial C levels are based on more than 400 total C measurements (0-20 cm depth) obtained from the experimental site in 1987 prior to experiment establishment. Multiple regression kriging with topographical information was used to create a detailed interpolated map of initial C values for the studied site. Then the data were analyzed using regression and geostatistical techniques. Effects of treatments and initial carbon levels on total C accumulation will be presented and discussed.
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