Biochar Application Methods Matter: Biochemical and Enological Responses of an Italian Field-Grown Grapevine (Vitis vinifera L.) Using Solid and Liquid Formulations

Viticulture is increasingly seeking sustainable practices that enhance grape quality while reducing reliance on synthetic inputs. Among bio-based strategies, biochar has attracted growing interest for its potential to improve soil fertility and influence plant metabolism. However, its effects can vary depending on formulation and application methods. This study evaluated the effects of the use of solid (SB) and liquid biochar (LB) on the biochemical and nutritional composition in leaves, berry skins, and must of a grapevine (Vitis vinifera L., cv. Sangiovese) cultivated in a vineyard in Tuscany (Italy). SB was applied once to the soil at 2.5% (w/w), while LB was applied five times/season at 10% (v/v) via fertigation. Results revealed formulation-specific effects on grapevine physiology and fruit composition. SB maintained leaf chlorophyll concentrations, increased total soluble proteins (+65%), total polyphenols (+57%), and tannin content (+33%) in berry skins and must, and reduced Cu and Zn. Conversely, LB reduced leaf chlorophyll concentrations (−24%) and nutrient contents (P, Fe, Cu, and Zn), but increased total flavonoids (+13%), antioxidant capacity (+20%), and vitamin C (+18%) in berry skins, alongside higher fructose and reducing sugars in musts. The findings highlight biochar’s potential as a bio-based input in viticulture, emphasizing the importance of formulation and application strategy. SB appears suited to long-term soil improvement and enhanced phenolic richness, while LB may modulate sugar metabolism for targeted enological outcomes.