Foliar Application of Biochar-Based Suspensions: Effects on Composition and Sensory Properties of Malvazija istarska (Vitis vinifera L.) Must and Wine

Foliar application of fertilizers and bioactive compounds helps viticulture adapt to climate change, while biochar (BC) derived from grapevine pruning residues (GPRs) represents a versatile material that further contributes to climate change mitigation. In this study, the foliar application impact of seven different formulations on the chemical composition and quality of must and wine of Malvazija istarska (Vitis vinifera L.) was investigated. The suspensions contained various combinations of BC, urea, and amino acids. BC increased the pH of the solutions in which it was present due to its alkaline nature, thereby influencing the uptake of nutrients and other compounds. Treatments C (control) and A (amino acids) led to the highest amount of yeast-assimilable nitrogen (YAN) (170 and 172 mg N/L). The amino acid profile of the must differed from the typical composition, with glutamine identified as the predominant compound. The combination of BC with urea and amino acids was associated with a higher sugar concentration in the must compared to the application of BC alone, ranging from 208 to 223 g/L. Combining BC with other components led to wines that received superior sensory evaluation scores compared to both C and B. BC alone did not influence must or wine quality. However, its application in combination with other components makes it a suitable carrier for such compounds. Due to its benefits, easy and cheap production, foliar application of BC suspensions with fertilizers can become a standard operation in viticulture and contribute to sustainable fertilization.