Organic amendments and mulches modify soil porosity and infiltration in semiarid mine soils

The restoration of soils affected by mining activities depends on the improvement of soil physical quality. This study aimed to determine the medium-term effects of organic amendments and mulches on soil physical properties and soil hydrological response. The experimental restoration was conducted in a homogeneous slope using a factorial design (organic amendmentsxmulches). The organic amendments consisted of compost from domestic organic residues, sewage sludge from an urban water treatment facility, and a control without amendment. The mulches consisted of gravel, woodchips, and a control without mulch. Modifications of the soil structure induced by the combinations of techniques were quantified by micromorphometric analysis of 2D porosity. Undisturbed soil cores were collected to determine the soil bulk density. Soil hydrological behaviour was determined by rainfall simulations. Samples from natural undisturbed soils surrounding the quarry were also taken as a reference. Restored soils with organic amendments have a higher total porosity than did nonamended substrates. Each restoration treatment combination resulted in a different pore system with very diverse hydrological responses. Organic amendments resulted in infiltration improvement and water erosion reduction. The woodchip mulch was more effective at trapping runoff and sediment, although this type of mulch did not favour vertical water movement towards deeper horizons. Therefore, the use of organic amendments should be encouraged in mine soil restoration and should be strongly recommended for its proven environmental benefits (enhancement of soil structure and infiltration and reduction of soil losses). However, the mulches did not produce the expected results in the tested arid-semiarid area.