Thursday, 13 July 2006

Terroir of Vineyards in the Northern Willamette Valley, Oregon.

Scott Burns and Dionne Starr Peace. Portland State Univ, Dept. of Geology, P.O. Box 751, Portland, OR 97207

Terroir, the relationship of geology, soil and climate to the quality of wines is so important to winemakers who want to have the best soil possible to produce the best wines, especially pinot noir. In a completely updated study of over 210 vineyards (5249 acres) in the northern Willamette Valley, the heart of the winemaking area of Oregon, two soil series are the dominant varieties of the vineyards, but three other soils have also shown great promise. The two dominant soils are the Jory (1504 acres), an Ultisol developed on 15 million year old basalt bedrock, and the Willakenzie (1245 acres), an Alfisol developed on marine sedimentary rocks of the foothills of the Coast Range. Both are very old soils (over 50,000 years old), well-drained, on south-facing slopes, xeric moisture regime, red, and located between 300' and 800' elevations. Alfisols have a few more nutrients in them than Ultisols. Three other soils with similar features are also being planted on with good results. Laurelwood soil (825 acres) is an Alfisol developed on mainly basalt with some old loess mixed in. Nekia (195 acres) is very similar to Jory (an Ultisol on basalt), but it is shallow (from 50-100 cm depth) compared to the Jory. The Yamhill series (333 acres) is developed on basalt, but it is not as old and is mainly a Mollisol with a thick A horizon. Soils developed on Missoula Flood deposits on the valley floors are not as well drained, and they have too many nutrients for the production of quality grapes. Our study shows that for the best terroir the best soils for producing great wines in Oregon are old, well-drained, xeric moisture regime and red.

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