A comparison of soil organic carbon stock in ancient and modern land use systems in Denmark.

During the South Scandinavian Early Bronze Age about 3300 years ago, thousands of burial mounds were constructed of sods from fallow ground used for grazing in Denmark and northern Germany. In some of these mounds a wet, anaerobic core developed, preventing the decomposition of organic matter. A comparison of the organic matter content in these mound cores and the plough layer in modern farmland offers an opportunity to compare the soil organic carbon (SOC) stocks in ancient and modern land use systems and to evaluate the long-term trends in carbon (C) sequestration in relation to modern farmland with varying inputs of manure and inorganic fertilizers. In the present paper we compare SOC stocks based on integrated horizon-specific densities and SOC contents in three 3300-year-old buried farmland soils, representing the land use system at that time, with results from soil surveys representing modern land use systems with low and high inputs of manure. Results show that, within the upper 0.28 m, which is the average depth of present day plough layers in Denmark, soils receiving manure from intensive pig or cattle production hold c. 60% more SOC than the ancient soils from the South Scandinavian Bronze Age. In contrast, modern arable soils mainly receiving limited inputs of manure hold a SOC stock similar to that of the ancient soils. [ABSTRACT FROM AUTHOR]