Legacy of medieval ridge and furrow cultivation on soil organic carbon distribution and stocks in forests

Abstract

Land management history can influence soil organic carbon (SOC) stocks over centuries. In this study, the impact of medieval ridge and furrow cropland management on SOC in forests was assessed. Continuous clockwise ploughing in rectangular fields moved topsoil from the outer part of strip-shaped fields towards the centre, thus forming a corrugated microtopography with peripheral furrows and central ridges. This tillage technique led to the burial of former topsoil under the ridges.The effect of this human-created microtopography and the centuries old topsoil burial on forest SOC spatial distribution and stocks was investigated. Five sites with ridge and furrow field strips under deciduous forests on soils of differing texture in Germany were sampled, with three orthogonal transects of the field strips and a defined reference position where neither net soil removal nor accumulation occurred. Reforestation took place between the 17th and 19th century.At 0 to 10cm depth, average SOC content was 28±3gkg−1 at ridges, 37±3gkg−1 at reference positions and 47±5gkg−1 at furrows. SOC stocks were 7±5% lower at ridges and 8±4% higher at furrows than at reference positions. Enhanced C input at furrows through leaf litter accumulation was indicated by higher SOC content in the free light fraction at furrows (10±5gkg−1) than at ridges (6±3gkg−1), higher specific SOC mineralisation (37±4μgCO2-Cg−1 SOC at furrows and 31±3μgCO2-Cg−1 SOC at ridges) and wider C/N ratio at furrows (18±1) compared with ridges (17±1).Buried topsoil under ridges (20 to 33–52cm depth) did not contain significantly less SOC than corresponding samples at furrows and reference positions. However, SOC content was 0.4 to 0.9gkg−1 higher at ridges than at reference positions, indicating long-term preservation of former topsoil SOC by burial under ridges, although enhanced SOC stocks at ridges due to carbon burial could not be significantly confirmed for all sites. It can be concluded that preserved microtopography over centuries and ancient topsoil burial, a legacy of medieval ridge and furrow cultivation, still influences forest SOC spatial distribution and stocks.