Soil chemistry as a measure of the distinctiveness of american viticultural areas of the Columbia basin, USA

The Columbia Basin, a semi-arid region centered in the eastern part of Washington State, is the second largest wine grape growing region in the United States and presently contains 10 American Viticultural Areas (AVAs). Eight of the Columbia Basin’s AVAs are smaller subdivisions (sub-AVAs) of the 46,100 km2 Columbia Valley AVA. Although legally distinct, the Columbia Basin AVAs are generally similar with regard to climate, landscape, and soils, the principle components of physical terroir.

To test whether the AVAs of the Columbia Basin are distinguishable based on the chemical properties of their soils, 53 samples were collected from vineyards considered to be representative within their respective AVAs. Sampled locations within each vineyard were selected as typical based on the advice of resident viticulturalists. Vineyard soils from the Willamette Valley and Snake River Valley, which are other major viticultural regions of the Pacific Northwest, were also sampled for comparison.

Soils were sampled from a depth of 50-75 cm and analyzed for bulk chemistry and plant-available nutrients. The analyses revealed that, of the 10 AVAs, only the Columbia Gorge, Walla Walla Valley, and Lake Chelan AVAs have distinct differences that could be attributed to variations in climate and parent material. Columbia Basin soils could be readily distinguished from vineyard soils of the Willamette Valley and Snake River Valley based on compositional differences that result primarily from variations in soil parent material and climate-controlled rates of weathering.