Every wine producing region in the world has its terroir, the mystical word that defines how climate, soils and geological conditions influence the quality of grapes. Soil and climate are the basic reasons why a Pinot Noir from Burgundy and Pinot Noir from New Zealand taste differently even though they are made from the same grapes. Climate is crucial for producing the best quality grapes but even more important is the soil, good soil, which provides a favorable root system for the vines.
Pedology and Edaphology
Soil is best described as a type of sediment, natural material is broken down by weathering and erosion. Sediments contain rock and mineral matter.
Before planting and growing a vineyard, careful pedological assessment of the area is vital. Equally important is the edaphological concept. Often referred to as ‘soil science,’ these two sciences, dedicated to studying the soil are essential in viticulture: pedology refers to the study of the formation of the soil while edaphology studies the influence of soil on the plant.
Soil is Important for vines
The primary function of soil and the subsoil (the layer beneath it) is to provide an anchor for the roots of the grape vines and to supply nutrients to the vines.
Soil will allow the vines to be well irrigated, with roots that will not become waterlogged.
Limestone or Chalky Soil
Calcareous soils have high levels of calcium and magnesium, both are excellent nutrients for the grapes. This type of sedimentary soil is ideal for grapevines because it allows easy absorption of minerals. In addition, it has good water retention properties, an advantage in periods of drought. Limestone-rich soil is key to good wine production.
Terra Rossa – Red Soil
Terra Rossa is a spectacular red clay soil. Rich in nutrients, it comes from the weathering of limestone. The red color is the result of the oxidation of iron deposits.
I reaked out to the Parker Coonawarra Estate in South Australia, which enjoys a mild climate, wet winters, and generally, high rainfall. Philip Lehmann from Parker Coonawarra Estate says:
“The red earth over limestone soils of the Coonawarra strip is undisputedly very good for growing red grapes – and most notably for the region, Cabernet Sauvignon.”
He said that the soft limestone could also hold a lot of moisture in the dry summer months, sufficient moisture, which the vines can draw upon to allow good flavor, color and tannin development.
Loam soil is an equal mixture of clay, sand and silt as well as some organic matter called humus. Occasionally, the soil contains more of one element than the others: sandy loam contains more sand, silt loam contains more silt.
As clay is heavier than sand and silt, clay loam tends to be heavy. Silt and Clay soils retain water effectively and will stop the roots from getting too large.
Volcanic soil, which comes from a volcanic eruption is rich in iron, potassium, magnesium and calcium. Mount Etna in Italy, Napa in California and North Island, New Zealand are wine growing regions that produce white wines from volcanic soil. The black soil is reputed to deliver water to the vines very slowly.
The Medoc region of Bordeaux is known for excellent Cabernet Sauvignon, which wine connoisseurs say is the result of excellent gravel soils of Medoc. The terrain is flat which poses a problem because of the high rainfall in the region, but thanks to the gravel, there is heat retention in the soil.
As the topsoil is stony, the vines have to reach down quite deep into the soil to get their nutrients.
Soil and soil management are crucial for producing excellent grapes, a challenging and intensive endeavor for viticulturalists but so very rewarding. Australian winemaker Mac Forbes from Mac Forbes Winery says enthusiastically:
“Due to the difference in our soils and climate, the key for me is to establish the best understanding of our own sites which should lead to more unique and individual wines."