Tracing Terroir: Soil Mineralogic Effects on Vitis vinifera,
Walla Walla, WA
Whitman College, Walla Walla WA 99362
Viticultural site individuality, or terroir, results from many factors, including climate, aspect, slope, bedrock geology, and soil chemistry. Although it has long been acknowledged that differences in wines are related to distinctive vineyard terroirs, some experts reject the idea that inorganic element content of the growth substrate contributes to these differences. The intent of this study is to test the idea that the concentrations of some elements in grape juice are directly related to the concentrations of those elements in vineyard soils. This study presents major and trace element abundances such as K, Rb, Ca, Sr, Fe, Zn, Mn, Zr and Mo in soil substrata, vines, and pressed juice of Vitis vinifera. In the Walla Walla Valley American Viticulture Area, vineyards are planted in three distinctive soils – basalt cobble loam, silt loam, and silt loam with underlying lacustrine substrata. Samples were obtained from one representative syrah vineyard from each type of soil. Chemical analyses of nine soil samples and 36 vine samples from each soil type were obtained with a Portable X-ray Fluorescence (PXRF) spectrometer. Chemical analyses of the grape juice samples were obtained by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Concentrations of Ca and Fe are 2 times higher and Zn and Mn are 1.5 times higher in the basalt cobble loam relative to other substrata. The silt loam sites have lower concentrations of Fe, Ca, K, Zn, and Mn and also retain more water than the silt loam with lacustrine substratum sites, possibly indicating leaching of elements in the silt loam site. A positive correlation between grape juice and soil for Fe was found, while all the other elements examined displayed negative correlations.