Verification of harmful subsoil compaction in loess soils

A Compaction Verification Tool (CVT) is presented to detect harmful subsoil compaction based on critical values of soil functions [saturated hydraulic conductivity Ks = 10 cm × d−1 and air capacity (−60 hPa), AC60 = 5 vol%] to provide a soil protection tool for legislative purposes. Harmful subsoil compaction is defined as follows: if these two soil functions fall below their defined critical value (degradation class IV) and if the percentage of measured values achieves 10 to <25%, the soil is classified as “assumed harmful compacted”. If the percentage is >25%, then the soil is classified as “verified harmful compacted”. The concept is tested using Luvisols derived from loess. Single and multiple dynamic loadings were applied at field capacity using a tractor-pulled single wheel load frame with three loads (3.3, 6.3, and 7.5 Mg). Unloaded reference profiles and loaded ruts of experimental plots were analysed, horizon specifically, using undisturbed soil samples to detect changes in Ks and AC60 in the top- and subsoil. According to CVT, harmful subsoil compaction could be only determined for the 6.3 Mg load (13%, “assumed”) and for the 7.5 Mg load (52%, “verified”) at the 40 cm depth for the multiple wheel passes. However, significant load-dependent reduction of AC60 could be detected down to 60 cm (E- and Bt-horizon) for the 6.3 and 7.5 Mg loads, and for Ks down to 40 cm (E-horizon).

► In this study a concept is presented (“Compaction Verification Tool”, CVT) which enables to verify harmful subsoil compaction. ► The concept is based on critical values of soil functions (saturated hydraulic conductivity Ks = 10 cm × d-1 and air capacity AC = 5 vol%) and displays the first soil protection tool for the legislator which is suitable as a conservation of evidence concerning subsoil compaction. ► Different field traffic intensities were simulated by single and multiple wheeling experiments including 3.3, 6.3, 7.5 Mg wheel loads to detect a boundary load in relation to the compaction status of arable Luvisols derived from loess. ► According to CVT, harmful subsoil compaction could be verified for 7.5 Mg wheel loads for multiple wheel passes and confirmed the applicability of the tool in arable loess Luvisols.