TERROIR OF HISTORIC WOLLERSHEIM WINERY, LAKE WISCONSIN AVA, PRAIRIE DU SAC, WISCONSIN

The viticultural history of Wisconsin extends to the 1840s, when Hungarian nobleman Agoston Haraszthy first settled on the current location of Wollersheim Winery in the Lake Wisconsin AVA. In this study, the terroir of Wollersheim Winery, a national historic site, is examined. A GIS analysis of geology, topography, soil, and climate is used in defining the Lake Wisconsin AVA terroir. Soil profiles, texture, major, minor, and trace element compositions, and mineralogy are utilized in establishing areas of variability within the vineyards; and also in comparing two specific vineyard plots, in conjunction with electromagnetic induction (EMI) and electrical resistivity tomography (ERT) surveys.

The Wollersheim Winery vineyards sit at elevations of 700-1000 feet and have south and southwest-facing slopes. Soil profiles, comprising horizons A, E, and B, were advanced throughout the vineyards to maximum depths of 70 centimeters. The soils are part of the Boyer series, consisting of very deep, well drained soils formed in sandy and loamy drift underlain by sand or gravelly sand outwash. Sand-sized grains dominate the textures of the vineyard soils. The XRF analysis of the fine fraction revealed the most abundant major elements (Si, Al, and Fe). Soil samples DR-1 and Lot-19-2 contained elevated Mg and CaO, demonstrating the influence of the Ordovician dolomite in the soils of the Domaine Reserve (DR) and Lot 19 plots.

EMI and ERT surveys were completed in the DR and Lot 19 plots cultivated with the same Marechal Foch grape variety. Based on the EMI data, the DR plot displays more variability and consists of more conductive soils. Two resistivity profiles completed at each plot (near the top and bottom vine rows) revealed little variability for Lot 19. Although the DR top row revealed similar resistivity values as Lot 19, the bottom row displayed much higher values. Thus, Lot 19 has a more homogeneous subsurface, whereas DR shows much more variability across the plot. In addition to these differences, other plot characteristics, including elevation, slope, and vine age variations further differentiate the two plots. The DR plot situated at elevations of 850-1000 feet, has a 20% average slope, and 40-year old vines; whereas, Lot 19 sits at lower elevations (700-850 feet), has a gentler average slope (10%), and younger (15-year old) vines.