The Dirt on Soil - Part 1

I was editing some of our marketing materials the other day, our fact sheet on our vineyard sources. And I was disgusted with myself because in it, I throw around soil types like Rouche silt loam and Selmac loam. And that is as far as I went. Now, unless my target market is limited to geologist enophiles, I couldn’t understand why in the world I threw that out there with no explanation. How many wine consumers know the benefits of Jory or Nekia soil? What makes Manita loam a great home for vines? Why is this info any consumer would want to know?

The wine industry as a whole has been striving to de-mystify and “un-elite” wine. Was I implying that only soil-educated consumers are worthy of our wine? Of course not. Simply, naming the soil is a quick, compact way to convey certain vineyard characteristics that can affect grape quality. And in my defense this document was meant for wine buyers, sommeliers and other industry folk. But, it’s also great info for anyone who wants to know more.

So, we’ll take a few blogs to check out the dirt on soil…

There are over 800 distinct classifications of soil in Oregon, and vineyards are currently planted on over 60 of them. (Campbell & Fry, Oregon Viticulture, 2003). There are three broad categories: clay, silt or sand. Other distinct characteristics of soils that influence vines include texture and structure, drainage, water and nutrient holding capacity, and pH.

Of these, texture and structure are the dominant qualities affecting vines, since they determine how deeply the roots will grow, and rate of drainage. Most of these influences are indirect. And many soil factors, such a how well it holds nutrients, can be managed in the vineyard through cover crops or even changing mowing schedules.

There has been some arguing lately in the wine industry press about that elusive concept of “terroir.” Many folks claim that when they drink wines from the great regions in France they can taste the minerals. But recent studies have found no scientific evidence that any detectable mineral compounds are present in the wines, and they suspect the taste differences between a grape grown in California versus one in France has more to do with climate than soil. (Wines & Vines covers the terroir issue quite frequently and thoroughly – I will post exactly in which issue these studies were featured once I track them down, although I believe it was late in 2006).

Next we’ll look at exactly what soil does influence, then we’ll take a closer look at some specific types of soil found in Oregon.