Since the end of the 19th Century, copper-based pesticides have been used in viniculture to prevent and reduce fungal diseases. The long-term application of copper-based pesticides in vineyard soils has resulted in soil concentrations significantly exceeding biological effect levels (above 55-65 mg Cu kg-1 ). A longer-term mitigation strategy to reduce the copper bioavailability in topsoil layers from vineyard soils is of key importance as there are currently little alternatives for copper in plant protection in organic viniculture. In the present study, we explore the application of organic soil additives - compost and biochar - which are both characterized by high heavy metal sorption capacity and soil amelioration potential. To evaluate the optimal biochar-compost-mixtures, six copper polluted vineyard soils from conventional vinefarms with different soil properties (differing in pH, organic C, texture, and Cu concentration) are treated with 12 different combinations of additives (including pure wood- biochar, pure compost, compost + wood-biochar (75:25), compost + wood-biochar (25:75), compost + 3 different activated wood-biochars (25:75), compost + wheat husk-biochar (25:75)). All combinations will be incubated for 8 weeks at constant temperature with 50% water holding capacity in three replicates. During incubation, respiration will be measured to evaluate differences in microbial activity. After 8 weeks, the desorption of copper will be determined. The additive mixtures that were most effective in terms of Cu immobilization will be chosen for potential enzyme activity measurements (cellulase, phosphatase, urease, chitinase, protease, phenoloxidase and peroxidase activity) to determine Cu and additive effects on soil microbiology. Furthermore, soil samples and seepage water samples of a greenhouse pot experiment with grapevine and cover crops including legumes will be analysed for their Cu-leaching in micro-lysimeters and DGT, their enzyme activity and the impacts on the microbial community by PLFA. In this contribution, we will present the design of the above-mentioned studies along with first results and conclusions.
