Abstract
AbstractMany soil types in the federal state of Schleswig‐Holstein (North Germany) are naturally compacted in the subsoil due to pedo‐ or geogenic processes (42% of the area) but, due to anthropogenic impacts, the percentage of subsoil compaction has increased further. To determine the overall subsoil compaction status of seven representative soil types in Schleswig‐Holstein (≤ 60 cm depth), air capacity (AC), saturated hydraulic conductivity (Ks) and effective bulk density (ρBeff) of 342 soil profiles from the database of the State Agency for Agriculture, Environment and Rural Areas of Schleswig‐Holstein (LLUR) were evaluated with respect to critical threshold values (AC < 5 Vol.‐%, Ks < 10 cm day−1, ρBeff > 1.7 g cm−3). The compaction status was classified into Classes I–IV, where a harmful subsoil compaction was assumed if both values of AC and Ks simultaneously exceeded (are smaller than) their threshold value (Class IV). Subsoils of (Stagnic) Luvisols and Stagnosols derived from glacial till, as well as those of Fluvic Gleyic Stagnosols of the marshlands, showed a high degree of natural compaction (46%–65% in Class IV). In contrast, sandy subsoil horizons of Podzols and Brunic Arenosols derived from glacifluvial sediments were rarely compacted (< 13% in Class IV), and possessed the lowest ρBeff, which were similar to Anthrosols. Only 5%–18% of their subsoil horizons exceeded the critical value of 1.7 g cm−3. Additionally, anthropogenic subsoil compaction of at least 6%–10% was verified for (Stagnic) Luvisols and Stagnosols.
Highlights
Soil compaction arises from natural or anthropogenic processes
Soil types, (Stagnic-)Luvisols and Stagnosols (Weichselian glacial region and “Higher Geest”) occupied the largest area, followed by the compacted or cemented subsoil horizons of the (Gleyic-)Podzols of the “Geest”, as well as the clayey horizons (“Knick”) or humus-rich buried A horizons (“Dwog”) of the Fluvic Gleyic Stagnosols in the old marshlands. These soil types/horizons were developed from different parent material. Their natural bulk density, air capacity (AC) and Ks can vary widely depending on the geogenesis and sedimentation processes (Figure 4)
The results show a similar risk of harmful subsoil compaction by further external stress applications, especially in undrained conditions
Summary
Soil compaction arises from natural (geo- or pedogenic) or anthropogenic processes. Pedogenic processes can cause compacted horizons like (petro-) duric, plinthic, calcic or gypsic horizons (Blume & Fleige, 2016), while in North Germany they mainly result from leaching and translocation of substances, like in the argic subsoil (Bt) horizon of Luvisols due to clay accumulation. 10% of German arable soils are estimated to be susceptible to compaction due to unfavourable structural conditions corresponding to a low internal stability against mechanical stresses indicated by the pre-compression stress value (Lebert, 2010) This proportion increased to 68%, when the soils are at a moisture level reaching field capacity (matric potential of -6 kPa). The verification of “harmful soil alterations” according to the German Federal Soil Protection Law (BBodSchG, 1998) requires the differentiation between the natural and the anthropogenic percentage of soil compaction This helps to secure evidence of potentially harmful soil degradation processes, like at cable construction sites (Zink, Fleige, Gebhardt, & Horn, 2013). To determine whether the compaction can be valued as potentially harmful, approved critical threshold values were used (Horn & Fleige, 2009; UBA, 2004)
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