Application of viticultural by-product biochar to alleviate soil copper toxicity in vineyard

The widespread application of copper (Cu) based fungicides in viticulture has led to significant copper accumulation in vineyard soils, threatening both ecosystem integrity and soil health. Reducing copper bioavailability in these soils is therefore crucial to promote environmental sustainability. Biochar, a porous carbon-rich amendment, offers a sustainable solution within a circular economy framework due to its well-documented sorptive properties, which allow biochar to immobilize copper, reducing its bioavailability in soils. This study evaluates the capacity of five biochars derived from vineyard by-products (grape marc, seeds, prunings) for retaining copper in soils through a percolation experiment. Results showed that copper concentrations in leachates were reduced by 20 to 98% in biochar-amended soils compared to unamended soils. Additionally, a phytotoxicity assay using Phaseolus vulgaris was conducted to assess biochar’s impact on plant growth and copper accumulation. Biochar-amended soils showed a reduction in copper pore water concentration ranging from 61 to 91% compared to the Cu spiked soil, which corresponded to up to four times higher plant growth. Furthermore, biochar addition restored soil hydrolytic enzymatic activities, with values fourfold higher than those observed in the Cu spiked soil. These findings highlight the potential of vineyard by-products derived biochar, and especially grape marc biochar as an effective tool to mitigate copper toxicity in contaminated soils, thereby supporting sustainable agriculture and the preservation of ecosystems and biodiversity. Biochars from vineyard by-products, especially from grape marc, reduced copper mobility and bioavailability in contaminated soils by up to 98%, demonstrating high immobilization efficiency. Copper immobilization was driven by strong sorptive interactions and a biochar-induced pH increase, which collectively altered copper speciation and reduced toxicity. Biochar amendments significantly improved Phaseolus vulgaris growth and restored key soil microbial enzymatic activities even under severe copper stress. Results highlight biochar’s potential as a circular, sustainable remediation strategy for mitigating Cu toxicity.