Compost and biochar interactions with copper immobilisation in copper-enriched vineyard soils

The novelty of this study is the inclusion of Cu speciation for investigating the effects of the soil additives. Differences between treatments were more pronounced for Cu2+ than for CaCl2-extractable Cu. All tested additive treatments in the acidic soil showed clear reductions of Cu2+ compared to the control without additives whereas this effect was less expressed but still recognizable in the neutral soil. In the soil pore water the Cu concentrations showed a Cu-mobilizing effect of the additives in the neutral soil, a mostly not significant effect in the acidic soil and a clear decrease of the Cu2+ fraction that was more distinct in the acidic than in the neutral soil. Although the Cu2+ fraction that was successfully reduced by the tested additives usually constitutes only <1% of total Cu in soil, this fraction is ecotoxicologically more relevant than the prevailing organically bound fraction.