Mark Chien, Penn State University
The physical properties of vineyard soils are critically important to wine quality, and, like soil chemistry and the food web, these attributes can vary dramatically yet still contribute to wine production.
The common denominator among all great vineyard sites is that they are well-drained. They strike a balance between adequate depth, good drainage, and water holding capacity so the vine will not suffer too much in summer, yet the soils will drain amply if late season rains afflict the ripening period.
Soil texture and structure, while closely related, describe different physical properties. Texture is the way a soil feels in the hand – like fine, gritty, or coarse, and is related to the relative proportion of sand, silt, and clay particles. Structure is the way particles are held together, described as platy, blocky, or granular. The space between these particles is also important as it provides for drainage and aeration. Adequate aeration is vital to the food web and root function. In evaluating a potential vineyard soil, soil pits are necessary to determine the physical nature of the soil at effective rooting depth – texture, structure, as well as chemistry and biology should be analyzed. Again, there is no substitute for an experienced eye and hand to complement lab results.
Soil surface characteristics are also an important consideration. The reflective and re-radiation effects of the soil are important parts of the quality equation, especially in cooler growing regions where every heat unit is needed to ripen the grapes fully. Cover crops will also have an effect on soils, both their drainage capacity and fertility. The use of herbicides and other chemicals will affect soils, especially over long periods as they build up. A soil should be analyzed with its history in mind as well. If it was a pasture, years of manure have added to its fertility. If it was a reputable peach orchard, perhaps it is particularly well suited to be a vineyard.
Reviewed by Eric Stafne, Mississippi State University
and Bruce Bordelon, Purdue University