Topsoil Organic Carbon Content

Abstract

Soil organic carbon (SOC) is a key soil component. SOC stores large amounts of carbon and it also affects water fluxes as well as the availability of nutrients. Soil water fluxes are impacted by SOC directly due to its effect upon soil hydraulic parameters. Also many indirect effects of SOC upon water fluxes have to be recognised, such as the impact upon plant growth and nitrogen turnover. SOC maps for all modelled soil layers in the DANUBIA simulation system for the Upper Danube watershed are therefore a necessary prerequisite to model plant growth, soil nitrogen turnover and soil water fluxes. For the majority of the Upper Danube watershed, these maps were easily derived from the 1:1,000,000 soil map (BÜK 1000, BGR, Bodenübersichtskarte 1:1 Million. Bundesanstalt für Geowissenschaften und Rohstoffe, Berlin, 1995). The BÜK 1000 distinguishes 33 different soil types within the Upper Danube catchment. Soil properties including SOC content are associated to soil-type-specific pedogenetic horizons. The SOC content and the C/N ratios for each of the soil layers were derived as a weighted mean of the SOC contents given for the BÜK 1000 soil layers. The BÜK 1000 does not cover areas outside of Germany. For these mainly alpine regions, the SOC contents were estimated using a three-step rule-based approach by (a) establishing a statistical relationship between soil-type unit and elevation, (b) estimating the SOC based on the assigned soil type and (c) selecting the predominate soil type for grid cells with multiple soil types (majority principle).