Development of the mechanical stability of a restored soil during the first 3 years of re-cultivation

Soil restoration is the process by which a soil that has been disturbed by excavation and displacement or by degradation is returned to its original state by means of active treatment. At the beginning of the process, restored soils are mechanically labile and susceptible to compaction. In this study, we monitored the regeneration of some physical soil quality indicators (bulk density, coarse porosity, penetration resistance) and the development of indicators of mechanical stability (precompression stress, compression index) of a refilled sandy loam originating from an Eutric Cambisol. In particular, we derived multiple linear regression equations to correlate precompression stress and compression index to soil texture, gravel content, organic carbon content and void ratio. During the 3-year observation period after restoration, bulk density and penetration resistance increased significantly, while coarse porosity decreased significantly. Nonetheless, these parameters remained in a range, which is considered to indicate suitable physical soil conditions for root growth over the entire period of observation. Precompression stress increased significantly in the topsoil as well as in the subsoil. The compression index was significantly higher in the topsoil than the subsoil and stayed fairly constant over the observation period. Precompression stress was negatively and the compression index was positively correlated with initial void ratio and to coarse porosity. Taking additional parameters into account, such as gravel content, clay content, silt content and organic matter content, improved the correlation with precompression stress. The equations derived with multiple linear regression analysis from our data set gave a satisfactory coefficient of determination for the compression index (r ² =0.81), but rather poor estimates for precompression stress (r ² =0.50).