Nutrient critical levels in soil and grapevines leaves to high-quality grape composition in subtropical climate

This study aimed to quantify the critical levels for soil and leaf nutrient content in grapevines based on must quality parameters and the nutrient output from the vineyards via grape must. During the two growing seasons, 207 vineyards located in Southern Brazil’s winemaking region, Serra Gaúcha, were evaluated. Six grape cultivars were evaluated at harvest time, the grape yield was determined, and fresh grape bunches were sampled for chemical analysis (pH, total soluble solids—TSS, total titratable acidity—TTA, total polyphenols concentration—TP, and total anthocyanin concentration—TA). Additionally, soil samples were taken from the 0.00–0.20 m layer to assess the fertility parameters. Soil chemical parameters and nutrient content in grapevine leaves were correlated to must quality parameters with the Boundary Line method. Critical levels for soil pH-H2O, soil organic matter (SOM), soil available P, K, Ca, Mg, Cu, Zn, and Mn content, cation exchange capacity (CECpH7.0), and Ca-Mg-K saturation (V) were proposed. Critical level values for leaf N, P, K, Ca, Mg, S, Cu, Zn, Fe, Mn, and B content were proposed for each cultivar and groups of cultivars. The mean macronutrient outputs from vineyards (kg ha−1 yr−1) were as follows: 10.6 (N), 5.7 (P), 44.9 (K), 2.3 (Ca), and 1.2 (Mg). Micronutrient outputs (g ha−1 yr−1) were 83.4 (Cu), 22.9 (Zn), 70.9 (Fe), and 27.5 (Mn). Fertilization management in vineyards can be adjusted and improved based on soil and leaf analysis reports, guided by these critical levels, thereby maximizing must quality for winemaking.