Issue link: http://winesandvines.uberflip.com/i/297564
34 W i n e s & V i n e s M AY 2 0 1 4 W I N E M A K I N G Keller, professor/researcher at Washington State University; Patty Skinkis, extension professor/researcher at Oregon State Uni- versity; Glenn McGourty, University of California extension specialist for Men- docino and Lake counties; Alan Lakso, pro- fessor/researcher at Cornell University, and Vivian Zufferey, viticultural researcher at Agroscope in Switzerland. I posed six questions to my panel; here are excerpts from their responses to four of them. Deep roots? It is often claimed that to express terroir, vines have to grow deep roots, penetrating beyond surface soils into bedrock and get- ting a wider range of mineral uptake than they would get from only shallow rooting. Is this true? Is it true only for some kinds of grapes/some kinds of soils? Choné: Not always true: In Bordeaux, Bur- gundy and in Napa (and not only in these regions), the best wine comes from vine- yards that are not deep rooted. Keller: I have yet to see a single peer- reviewed paper on this subject. The scien- tific evidence is heavily on the side that most mineral uptake occurs in the shallow topsoil (the top 1 or 2 feet), where available minerals are concentrated. Moreover, oxy- gen availability declines with depth, which hinders root respiration, and respiration is necessary to fuel active mineral uptake. (There is very little passive uptake except, undesirably, for calcium.) McGourty: Roots don't grow into bedrock! They may grow in fissures and fractures in the bedrock, but roots won't penetrate most substrates with a bulk density > 1.8 g/cc. Most rocks start around 2.4-2.6 g/cc. (There is) no real data that I am aware of to make a good case. There certainly are great wines that come from sites with deep alluvium, but realistically, most root activity is in the upper 18 inches of soil where oxygen can easily diffuse. Smart: Lot of bull****. I do not see why deep roots would provide a better environ- ment than shallow roots. Even for vines with deep roots, near the surface is where most of the roots are. Van Leeuwen: One of the most widespread wrong ideas is that terroir expression is mediated through deep-rooting vines pick- ing up minerals from deep soil layers and transforming them through some mystical processes into aromas that make the terroir expression of great wines. There is no sci- entific evidence for such a statement. Min- erals (except nitrogen) play a limited role in terroir expression. Water is the key factor. Dry farming? Most terroir proponents insist that distinc- tive wines can only come from unirrigated vineyards, and that irrigation guarantees bigger crops and less character. Is that true? Or can irrigated vines in dry climates create distinctive grapes? Skinkis: There is no direct link between dis- tinctive wines and irrigation use. From a plant-science perspective and viticulture perspective in particular, water is a neces- sity for all plants. In vineyards, water is required through irrigation when there is not sufficient water provided by precipita- tion and stored in the soil. Whether a soil is "non-irrigated" or irrigated, the vines still require water. Zufferey: Irrigated vines in dry climates can lead to distinctive wine qualities (particu- larly with white cultivars). Controlled irri-