Vertical bulk density distribution in C-horizons from marley till as indicator for erosion history in a hummocky post-glacial soil landscape

For a quantitative understanding of water and element balances of intensively cropped hummocky post-glacial soil landscapes, effects of erosion and colluviation on pedologic structure, and mechanical and hydraulic soil properties should be considered. The C-horizon consisting of glacial till as the parent material can be close to the surface and become part of the plant root zone at exposed locations where topsoil was removed by tillage erosion. Soil bulk density, as one parameter for hydraulic pedotransfer functions, may be characteristic also for the depth location of soil horizons. We propose bulk density as a proxy for the spatially distributed vertical distances between the C-horizon and the soil surface in such landscapes. We analyse the relation between bulk density and depth location for the C-horizon in Luvisol and Regosol soils of various stages of profile reduction by erosion. Within the same diagnostic soil horizon, the bulk density data increased with depth; however, within the C-horizon, the bulk density remained similar or showed a small tendency to decrease with depth. Highest bulk densities of more than 1.8 g cm−3 (soil <2 mm) were found in the uppermost C-horizon of the Haplic Regosol. With a model of bulk density based on sand and organic matter contents as well as soil depth, bulk density values of these C-horizons were adapted. The factor of the regression function was increased as a result of calibration by a constant of 0.3 g cm−3. The calibrated model was then used to reconstruct a hypothetical vertical profile of the bulk density for the heavily eroded Haplic Regosol indicating a soil loss of at least 1 m. The bulk density modelling for estimating the vertical position of soil horizons in the original (non-eroded) soil profile could possibly be used for the estimation the topsoil removal rate by erosion for soil types at a certain landscape position. The erosion history may thus be estimated by reconstructing standard bulk density profiles developed in locations where the topsoil removal rate was relatively fast as compared to the soil development processes and the bulk density not in equilibrium with the overburden load.