Optimizing the combined application of amendments to allow plant growth in a multielement-contaminated soil

This study was aimed to 1) properly understand the dynamics of toxic elements (Al, Fe, Mn, Cu, Pb, Zn and As) in a sulphide-mine soil after combined application of compost from urban sewage sludge (SVC) and bottom ashes from biomass combustion (BA) and to 2) optimize the combination of both amendments for vegetation growth. Soil was amended following a D-optimal design and the mixtures (15 in total) were incubated during 30 d. At the end of the incubation, the effects of amendments on the assessed variables as well as the process modelling were evaluated by Response Surface Methodology (RSM). The process modelling confirmed that quadratic models were adequate to explain the behaviour of the assessed variables (R(2) ≥ 0.94 and Q(2) ≥ 0.75). Both amendments significantly increased pH and electrical conductivity, while reduced metal extractability. A different behaviour of As respect to metals was observed and high doses of BA sharply increased its extractability. The optimization process indicated that adequate conditions for vegetation growth would be reached adding the soil with 6.8% of SVC and 3.1% of BA (dry weight). After amendments application the germination and root elongation of three energy crops were significantly increased while lipid peroxidation was decreased. Therefore, the combined application of SVC and BA to a contaminated soil could improve soil conditions and might be expected to have an advantage during plant growth. Moreover, the RSM could be a powerful technique for the assessment of combined amendment effects on soil properties and their effective application in multielement-contaminated soils.