Temporal and Spatial Variability of the Soil Macropore Tortuosity of Marshland Soils in Northern Germany as Influenced by Soil Management Including Liming

The soil oxygen diffusion coefficient (Ds) was determined for structured topsoil (0.1 m) and subsoil (0.3 m) samples of a clayey and a silty marshland soil, classified as Haplic Gleysol. The undisturbed soil samples were equilibrated to a soil matric potential equal to -6 kPa, excavated 7, 12, and ≥24 months after liming with a double chamber system. No lime, and either limestone (CaCO3) or quicklime (CaO) was incorporated each in two intensities into the ploughed topsoils at two sampling sites. In combination with the values of the airfilled and total porosities, and with the help of a linear fitting factor, f, measured gas diffusion coefficients were fitted to the Millington-Quirk (MQ) tortuosity model to better match simulated and measured Ds values. Seven months after lime application, the f–values ranged between 0.013 and 0.500, indicating a more tortuous pore systems than predicted by the MQ model (f = 1). The f–values increased continuously with time or were highest 12 to ≥24 months after CaO application for the topsoils. For each subsoil, the values were in the same order of magnitude after 7 and 12 months and increased ≥24 months after lime application. The results show, that the soil macropore tortuosity as reflected by the f–value is highly dynamic at the time and spatial domains. The direct effects of liming on the f–values cannot be determined due to several interactions between liming and biotic, abiotic, and management-induced soil aggregate formation processes. The results indicate that the f– values increased with liming and that lime-induced soil structural changes are not spatially restricted to the topsoil layer where the lime had been applied.