Biochar improves the fertility of a Mediterranean vineyard without toxic impact on the microbial community

Incorporation of biochar into agricultural soils has been repeatedly proposed as an effective strategy to mitigate climate change with beneficial effects on soil properties and crop production. Results from previous field experiments showed that, when applied to vineyards, biochar amendment increased yield without a negative impact on grape quality, decreasing water stress during droughts and improving soil physical and chemical properties. Despite those positive impacts, the long-term effects of biochar treatment on soil fertility and ecological toxicity have seldom been studied at a real farm scale. We investigated the effects of biochar amendment on vineyard soil subjected to a single and a repeated biochar application focusing on total heavy metal concentration and availability, concentration and persistence of polycyclic aromatic hydrocarbons (PAHs), soil toxicity, and soil microbial community structure over a 5-year period. Our results showed that a longer term biochar application in a vineyard has no impact on soil microorganisms and does not retain toxic compounds (PAH and heavy metals). For the first time in biochar research, we investigate the biochar effect on a perennial crop and correlate the PAH retention with soil microbiota. Our research demonstrates that biochar application in a Mediterranean vineyard does not have a negative impact on soil ecology, reinforcing the perception that biochar is a sustainable option at farm scale, meeting the needs of agronomy and climate change mitigation.