Assessment of Organic Waste- and Biomass-Derived Amendments for the Cultivation of Eucalyptus globulus Labill. in Marginal Soils Affected by Pyrite Mining

Abstract

The combined use of soil amendments and beneficial microorganisms represents a promising strategy to restore degraded mining soils by improving soil properties, immobilizing contaminants, and supporting plant production. A pot experiment was carried out with soils from the Aljustrel mining area (Iberian Pyrite Belt, pH 3.9, contaminated with As, Cu, Pb and Zn in quantities of 4782, 1596, 8652, and 938 mg kg−1, respectively). The amendments tested included biochar (64 g kg−1), municipal solid waste compost (64 g kg−1), their combination, and ground oyster shell (11.3 g kg−1, with liming capacity similar to CaCO3), combined with compost. Eucalyptus globulus Labill. was selected because of its major economic importance in Portugal, and an arbuscular mycorrhizal fungus (AMF) (Rhizophagus irregularis) was inoculated. After five months, the combined application of compost and biochar increased soil organic matter from 1.4% to approximately 6% and resulted in the highest aboveground biomass production (53.8 g plant−1 dry weight). The combination of compost and ground oyster shell increased soil pH to approximately 6.5 and was associated with lower Cu and Zn concentrations in aboveground plant tissues, by 49% and 70%, respectively, compared with the corresponding unamended treatment. This treatment also increased soil dehydrogenase activity, while AMF inoculation had a significant effect on this parameter despite the absence of detectable root colonization. The available water capacity increased significantly in the biochar and in the biochar–compost combination. Results show that the combined use of waste- and biomass-derived organic amendments and liming materials can improve selected soil properties in acidic, multi-element contaminated mine soils, supporting eucalyptus establishment.