A comparison of the organic matter content in anaerobic soil horizons in burial mounds and the plough layer in modern farmlands offers a unique opportunity to compare the soil organic carbon (SOC) stocks in ancient and modern land use systems and to evaluate the long term carbon sequestration in modern farmlands during thousands of years in relation to inputs of manure, fertilizers, liming and drainage. In this paper the SOC stocks from anaerobic soil horizons in two big loamy burial mounds from the Viking Age, representing the land use system 1000 years ago, are compared with results from ancient sandy soils, loamy soils surrounding the mounds and nation-wide soil surveys representing modern land use systems with low and high inputs of manure. Results show that within the upper 0.28 m of the soil, which is the average depth of present day plough-layers in Denmark, the carbon stock in the farmland soils surrounding the mounds is roughly 85% of that in Viking Age. Intensively manured loamy soils in West Jutland contain about the same carbon stock as the ancient soils from the Viking Age. In contrast, modern arable loamy soils in Southern Zealand and adjacent islands, receiving low input of manure, contain a SOC stock of roughly 60% of the level in the loamy Viking Age soils. The carbon loss since the Viking Age in the surrounding soils is believed to be due to liming and drainage that has increased the decomposition of organic matter in the soils. This loss can be balanced by present day land use systems with high input of manure. Compared to ancient sandy soils that do not show any SOC loss during the past 3000 years, there is a clear SOC loss from the loamy soils, probably about 40% during the last 150 years, where most of the loamy soils have been drained.
Agriculture, Ecosystems and Environment, 2013, Vol 174, Issue 174, p. 49-56
Carbon stock; Climate change; Viking Age; Land use; Modern farming; Burial mound