Assessing the reversibility of soil displacement after wheeling in situ on restored soils

Land restoration after open-cast mining and construction sites enables maintaining the quantity of agricultural land in the long-term. With the modern gentle restoration techniques, soil is heaped loosely and supposed to consolidate and increase its mechanical resistance in the first few years after restoration. With this study, we investigated the influence of the soil's age after heaping on the susceptibility to compaction of restored soils.We carried out wheeling experiments with a tractor and a manure trailer on two adjacent restorations of 1 and 3 years after heaping, respectively. Subsequently we observed the soils for 3 months. We assessed soil displacement at the soil surface with digital levelling, and within the soil profile in 25–30 cm depth with a special hydrostatic soil displacement meter (HSDM), which had been developed for this application. In the same depth, soil cores were taken to determine coarse pore content and bulk density, right after the wheelings and at the end of the experiment.We conducted four wheelings, what caused soil displacements at the soil surface of ca. 11 mm on both restorations. The HSDM provided us reliable data for the 3-year-old restoration, only. Total soil displacement after the four wheelings was ca. 5 mm in 28 cm depth. Our subsequent observations revealed the complete decline of the soil displacements caused by the wheelings within 18 days at the soil surface as well as in the soil profile. The levelling results revealed the same recovery from the displacements at the soil surface for both restorations independently of their ages.For the soil physical parameters, we found differences between the two restorations. Only the 3-year-old restoration showed less coarse pores and higher bulk density in the track than beside the track right after the wheelings, while the 1-year-old restoration did not. At the end of the experiment, coarse pore content and bulk density in the tracks stayed approximately the same, as right after the wheelings, particularly the track of the 3-year-old restoration did not show any recovery. Because of the partly contradictory results of soil displacement measurements and soil physical parameters, we recommend further research on soil deformation and the regeneration of restored soils.