Field-testing and characterization of Technosols made from industrial and agricultural residues for restoring degraded slopes in semiarid SE Spain

Many industries and agriculture generate huge amounts of wastes either mineral, organic or both, with environmental impact. Some of these residues have the potential to become Technosols when mixed in proper proportions. Degraded terrestrial ecosystems, especially sloping land, show very shallow or no soil left which makes restoration very difficult. Covering such degraded surfaces with Technosols might be a possible solution. The purpose of this paper is to show how some combinations and proportions of residues, mainly sludge from the ornamental stone industry and compost from green residues, become useful Technosols for landscape restoration. We tested in the laboratory twelve different combinations of that sludge, organic compost and other materials, as experimental Technosols. The three best combinations were tested in the field in (3 × 2 m) experimental plots at the open air on a 30° slope. We planted autochthonous species and survival and growth monitored for 1 year. The essential soil physical and chemical properties were also monitored as well as their hydrological behavior by means of repeated rainfall simulations. Treatments with artificial stone sludge up to 70% and slabs were able to provide substrates with physical and chemical properties relatively similar to those of natural soils in arid-semiarid environments like those from SE Spain. Higher content of organic matter and better physical properties were found in the Technosols. No clear differences between types of treatments were detected. Although runoff was slightly higher in Technosols than in natural soils, the treatment with the highest compost content (15%), presented the lowest erodibility, similar to natural soils in the area. None of the tested Technosols produced dangerous leachates exceeding the maximum values recommended by the European legislation. Technosols also increased plant growth of Rosmarinus officinalis and Thymus vulgaris. These results confirm that the tested Technosols can be used for the restoration of degraded soils and, in areas affected by earthworks, as road taluses.