Numerous studies have reported substantial changes of soil organic carbon (SOC) stocks after converting forests into agricultural land and vice versa. However, some studies suggested that agricultural soils might contain similar amounts of SOC as forest soils. Losses of SOC induced by cultivation might be overestimated due to shallow soil sampling and application of inaccurate pedotransfer functions. We investigated the impact of different land uses on total SOC storage down to the subsoil on the basis of 270 soil profiles in southeast Germany under similar climatic and pedogenic conditions using an equivalent soil mass (ESM) approach. Land use effects on SOC storage were strongly affected by soil class, which comprised soil types with similar pedogenesis. Both slightly lower (<20%) and even higher SOC stocks were found under cropland compared with forest land for different soil classes. A comparison of different soil classes under grassland and forest land also showed no considerable differences of SOC stocks. Soil cultivation may not generally be associated with a strong decline of SOC, as tillage probably promotes the formation of organo-mineral associations and a relocation of SOC with depth may decrease its decomposition. This finding should be taken into consideration when estimating and managing the emission and sequestration of C in soils. We assume that many studies based on topsoils alone may have underestimated agricultural SOC stocks, particularly when an ESM approach is used. Our results highlight the need for soil type-specific evaluations in terms of interpreting the effects of land use management on SOC stocks.
