When approaching the topic of viticulture, analysing the soil profile of a certain area is one of the most important factors to consider. The role of the soil in viticulture is to facilitate the uptake of water and nutrients through the vine roots.
The soil is made of layers. The uppermost layer is the topsoil, an ideally thin layer supporting most of the vine’s root system and including most of the feeding network. However, the main roots also penetrate several layers of subsoil, deeper in the ground, which determines drainage, roots depth and how the vine collects minerals.
In general terms, suitable soil types for viticulture should provide the right balance between drainage and water retention. According to these features, it’s evident how different soils are more or less suitable for growing vineyards in different climates.
Classifying soils is a notoriously tricky task as vineyards are often rooted in different types of layers, with different conformations in adjacent plots. These differences contribute to variety, including characteristics such as minerality, with elements contained in specific soils benefitting specific grape varieties more than others.
Such variety represents one of the pillars of the highly debated concept of terroir and one of the reasons why wines taste differently despite sharing elements such as grapes, climate and winemaking techniques.
Soil types can be classified in very detailed sets, but most of them fall under a broad category.
Made of large particles, sandy soils are known to offer good drainage and to retain heat. This type of soil might not hold nutrients efficiently, yet it prevents diseases such as phylloxera. Wines from this type of soils are usually fresh and aromatic. Despite other soil types in the region, some of the finest examples are to be found in Tuscany, Piedmont and Graves in Bordeaux.
Clay soils also hold water but remain cooler, especially when combined with lime. In terms of drainage, the main issue is represented by climates with high rainfall. Wines from clay soils are quite bold and reds are high in tannins. Vosne-Romaneé in Burgundy is renowned for its most acclaimed Pinot Noir.
The fine texture of this type of soil provides good retention of both water and heat, yet it’s more prone to hazards such as waterlogging. Wines from silt soils tend to be rounder and smoother, with lower acidity.
It’s a combination of several types of rock, including clay, sand and silt. Quite soft and fertile, loam is not associated with quality wine-making due to the vigour and less concentration to the fruit. Vineyard management is key to good quality here. Examples of this soil type can be found in California, namely in Napa Valley and Sonoma.
Napa Valley also includes several examples of alluvial soil: very fertile too, it’s a combination of gravel, silt and sand. Alluvial soils are rich in organic materials. Vineyard management proves to be a trustworthy ally here, too. Wines from alluvial soils are less aromatic and acidic.
For premium winemaking, limestone soils are considered a true gem due to their water holding capacity in dry weather and drainage in much wetter climates. This type of soil reflects sunlight, promoting photosynthesis and increasing nutrient exchange between the soil and the vine. Wines tend to be aromatic and elegant. Famous regions featuring limestone-rich soils are Champagne, Chablis in Burgundy and Saint Emilion in Bordeaux.
This soil type is made of cooled and solidified lava, turned into rock and eventually broken down into soil. Very common in Sicily, volcanic soils offer good drainage as well as heat and water retention. They are also naturally high in iron.