Reference Nutrient Levels in Soil and Leaves for Vines Cultivated in a Subtropical Climate Using Boundary Line

The study aimed to establish nutritional reference values in the soil and leaves of Vitis spp. vines, cultivated in a subtropical climate to obtain high yield, using the boundary line (BL) method. The research was conducted in the 2021/22 and 2022/23 harvests, in the Serra Gaúcha region, Southern Brazil, one of the main winemaking regions in South America. Six cultivars were evaluated: four Vitis labrusca (‘Isabel’, ‘Bordô’, ‘BRS Magna’, and ‘BRS Lorena’) and two Vitis vinifera (‘Pinot Noir’ and ‘Chardonnay’). A total of 207 vineyards were evaluated, and seven plants were selected and marked in each vineyard. Complete leaves (blades + petiole) opposite to the bunch were collected to evaluate total nutrient contents during flowering. At harvest, soil samples (0.00–0.20 m layer) were collected for soil fertility evaluation, and the number of bunches was counted to estimate yield. The relative fruit yield (RFY) was related to soil chemical attributes and foliar nutrient contents through scatter plots, using the BL method to obtain soil fertility classes and nutrient sufficiency ranges. The sufficiency ranges considered adequate in the soil for pH(H2O), soil organic matter, P, K, Ca, Mg, Cu, Zn, Mn, CECpH7.0, and Ca-Mg-K saturation were proposed. Also, the nutrient sufficiency ranges in the leaves for N, P, K, Ca, Mg, S, Cu, Zn, Fe, Mn, and B were defined. These results will contribute to greater accuracy in fertilization, maintenance of high grape yields, reduction of environmental impacts from excess fertilizers, and reduction of viticulture production costs.