Variations in the soil properties of the premier vineyards of the Columbia Basin : implications for terroir

The Columbia River Basin of Washington is the second most productive wine region in the United States. Most Columbia Basin vineyards lie within the Columbia Valley and Columbia Gorge American Viticultural Areas (AVAs), which together include 46,862 km² in Washington and north-central Oregon. Eight sub-AVAs have been recognized within the Columbia Valley AVA. TheseAVAs contain many soil types, which have implications for the terroir of the vineyards.

Most soils in the Columbia Basin are derived from loess that overlies basaltic bedrock and Pleistocene Missoula Floods deposits. The influence of the underlying Miocene Columbia River Basalt bedrock on soil chemistry is highly variable and is controlled by loess thickness, as well as the topography and degree of weathering and soil development that has occurred at each site.The 65 soil samples analyzed in this study were collected in the summer of 2010 from vineyards recognized for providing high quality grapes that have been made into high quality wines. The samples are primarily from the Columbia Valley AVA. Sampling sites were selected to be representative of each vineyard and vineyards were selected to representative of the variations in terroir within their AVA. Multiple samples were taken from vineyards with large spatial extents and/or variations in elevation.The samples were analyzed for texture, bulk chemistry, and abundances of plant-available elements.

The textural and chemical analyses from each site in the Columbia Basin were compared to determine the range of values within each AVA and to discern any AVA-specific trends and the relative influence of basalt bedrock. The results from the Columbia Valley AVA sites were also compared to sites outside the AVA. Within the Columbia Valley, soil textures range from sand to silt loam. Columbia Valley sub-AVAs have soil properties that display wide ranges of values, but this variability does not occur systematically between the sub-AVAs and thus the AVAs cannot be distinguished from each other on the basis of their soils. The exception to this is the Lake Chelan AVA, the only Columbia Valley sub-AVA with glacial deposits derived from granitic bedrock as its parent material, resulting in unique soil chemical properties that reflect that difference in substrate. The range of chemical properties of Columbia Valley AVA soils is distinct from the properties of other northwest AVAs. Therefore, based on these properties, the Columbia Valley AVA can be distinguished from the Puget Sound, Snake River, Columbia Gorge, and Willamette Valley AVAs.