Edaphology is the science which studies the soil's influence on living organisms, especially plants. The selection of a potential vineyard site should include an edaphologic study. The content and type of soil is pertinent to healthy vineyards and their sustainability. (Read on in "How Pedology and Edaphology Affects Viticulture.")
Vineyard Soils 101
Before getting into all the details that encompass vineyard soils, it might be simpler to address what the grapevine needs and alternatively, does not need.
The best vineyards, which produce the best fruit, are the locations that allow the grapevine to struggle. The more stress a grapevine undergoes, the better it can grow the best fruit for making better wine. The vine itself has a remarkable ability to adapt to geographical and climatological stresses, such as little access to water, elevation and excess heat. One of many ways vines combat stress that many might be familiar with is the vine's ability to produce resveratrol.
Unlike many other plants, grapes do not need to be planted in nutrient rich soils for optimal production. The best vineyards are those planted in soils with a high mineral content. Additionally, there are other factors to look at, which can influence the function of soil. These factors happen to be the same for choosing where a vineyard can be cultivated. (Read "Soil Types and the Wine Grapes That Grow Best in Them.")
Basics of Vineyard Site Selection
There are four things to observe when looking for a vineyard location; the first is the site's elevation. This may be elevation in relation to sea level or the elevation on the site itself. Next, the slope or the inclination of the land which is important when planting grapevines. It allows for easier hand harvesting and access to sunlight for the vines. (Read on in "Why Are Most Vineyards Placed on Slopes and Hillsides?")
Number three on the list of things to consider is the orientation of the land. Does the site face north, south, east or west? And finally, we need to consider the land's history and ask the following questions. "What was previously grown on the site? Or is there a specific vegetation currently growing on the site?" "Were chemicals utilized?" "What weeds are present?" "Is there a record of any diseases which were/are present on the site?" (Learn more in "Pedology 101: The Process of Vineyard Site Selection.")
Avoid These Soils for Vineyard Sites
The list of proper soil types for grapes is lengthy. This can be proven just by looking at a list of famous soil types from around the world where well-known wines are made. So to simplify things, we will only talk about the soil types to avoid.
These types of soils are not always located in wet regions. The structure of the soil should not have the ability to retain high contents of water. For example, a site predominantly made of up clay is undesirable because the vine should not have easy access to water when possible. Clay has the ability to hold high concentrations of water for long periods. Grapes have the ability to grow roots as long as twenty feet (six meters) in search of water.
The exception to the rule might be a soil with a lower percentage of clay in the soil's overall content. A shallow layer of clay beneath the topsoil, located in the hardpan can be interesting, especially where dry-farming is enforced. A mixed combination soil of sand and a little clay can also be beneficial. The clay will have the ability to hold water reserves the vine can access in times of extreme drought and sustain itself.
Overall, soils on the site should have good drainage and a high infiltration rate.
This may come as a surprise to those new to wine and especially those with a passion for gardening. However, the grapevine, unlike say your garden vegetables, does not need high levels of essential nutrients. As vines have the ability to grow roots in search of water, they also look for the nutrients they need. If a vine were to have these readily available, fruit production would be in excess and the quality of the fruit for wine would be very poor.
It goes back to the general rule that grape vines must struggle in order to produce quality fruit for wine.
Remember that two of the main criteria for selecting a vineyard site should be the consideration of elevation and slope of the land? Despite the soil's content, these elements have a role in the production and function of the soil. Higher elevations and its inclination will aid in good drainage.
While these low-lying regions may not always have significant amounts of water that can be damaging to vineyards, they are prone to flooding. In addition, the water table is often within easy reach to growing vines. A vineyard does not always have to be at a minimum elevation in relation to sea level, however, it should be located and planned at a site which is high in relation to accessible ground water.
An edaphalogic study of a potential vineyard site can save a lot of time and investment in something that may not be ideal for cultivating wine grapes. While we have addressed the types of soils to avoid, other factors as mentioned under "Basics for Choosing a Site" in number four is just as important. A thorough edaphalogic study will determine the content of a soil as well as its function and practicality for vineyard production.