What Kind Of Soil Do Grapes Need – Wine is one of the most valuable products that depends on its regional identity. Its geographical and geological origin certainly makes a difference, and the soil in which the vine grows is a major part of it.

The Oxford Companion to Wine 2015 edition defines soil as ‘minerals in the earth’s crust formed by the weathering of transported sediments from the underlying rock or soil parent material.’ Soil is rich in decaying plant and animal remains that form organic matter, often called humus.

What Kind Of Soil Do Grapes Need

What Kind Of Soil Do Grapes Need

Soil serves several incredibly useful functions—first as a physical anchor for plants to take root, but also as a source of water and nutrients that plants need to sustain life (in addition to producing glucose and oxygen through photosynthesis).

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Historically soil has been closely linked to terroir, especially in the Old World, but increasingly the New World is interested in discovering what makes good vineyard soil using techniques such as precision farming, soil mapping and foliar nutrient status analysis.

Currently, the scientific opinion is that the physical characteristics of the soil are the most influential and among these physical characteristics, water supply is the most important characteristic. A good vineyard soil will drain well enough that the roots will not be flooded, but will also be able to store enough water to provide an adequate supply during the growing season, even if rainfall is erratic. Of course, when irrigation is used, the water storage part is not so critical, but most of the world’s vineyards are still dry farms and depend on nature’s bounty for sufficient water.

Other important aspects of the soil to consider are its structure (so the size of the particles that make it up and how easy it is for water to drain and root penetration); depth (shallow soils and impure rocks may be susceptible to early drought); aeration (better for decomposing fauna and organic matter such as microbes and earthworms); nutrient status and even color (for example dark soil absorbs sunlight better than pale soil and can return heat to the plant later at night).

Soil fertility is a critical factor and it is known that very fertile soil is not considered good for quality wine production. There’s no real connection between the actual minerals or flavor compounds in the soil (and the hot topic of ‘minerals’ is one for another article) but the fertility levels affect how the plant grows and the quality of the fruit it produces.

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Nitrogen is especially important, and high nitrogen compounds mean fertile soil, which usually means stronger vines. This means poor color, leafy flavors, excess potassium and high pH due to too many shady leaves on the fruit. Or it can mean over-cultivation and a lack of concentration and flavor.

Globally, it is common knowledge that the best wines come from less fertile soils that are less energetic and naturally more concentrated. On the other hand, a lack of nitrogen in fruit can mean problems with fermentation and decline (usually due to smelly sulfur-containing compounds such as hydrogen sulfide and mercaptans).

Some of these problems can be managed by adding compost or manure or yeast nutrients for fermentation, or conversely by planting cover crops to utilize excess nitrogen. Organic matter contributes to available nitrogen and adds water-holding capacity to dry sandy soils, and on heavy clay soils it helps provide friability and aeration.

What Kind Of Soil Do Grapes Need

Certain soil types are usually associated with high quality wines. Chalk is a soft, crumbly and highly porous type of limestone (based on the mineral calcium carbonate) and is usually very pale in color. It is valued in viticulture because it drains well but the pores in the subsoil rocks also have a high water storage capacity and because it is porous the roots can easily penetrate this subsoil. The fertility of chalk soils is also reduced, which is another advantage because it is easier to add nutrients than to reduce them. Southern England also has good chalk soils, but Champagne is the most famous example.

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Limestone has a calcium carbonate mineral base but is harder so roots can only penetrate through cracks. Some particularly famous vineyard soils are limestone-derived – the rusty red terra rossa soils of Coonavara and Croatia cover the limestone. One disadvantage of high levels of limestone is that the soil can become alkaline, which can cause leaves to turn yellow and cause a condition called chlorosis, where they cannot photosynthesize effectively. It is often caused by a lack of iron (absorption of zinc, manganese and boron can also be a problem) and the main solution is to plant on lime-tolerant rootstocks such as Fercal or 41B.

Clay is made up of very fine particles of clay minerals (phyllosilicates) that hydrate (ie have water in the crystal structure). Accordingly, clays have good water holding capacity, but this means that they can become waterlogged or cold (wet soil takes longer to warm up). Clay often also contains other minerals, so the famous marl of the Côte D’Or is a mixture of clay with a high calcium carbonate content.

Loess is an accumulation of clay and silt, usually deposited by the wind, which is good for vines because it is porous and easy to grow. Tokaj is a region famous for its los.

Tuff is a fine-grained volcanic rock formed from ash material erupted by volcanoes. It is a relatively soft, easily weathered soil and very useful for excavating cellars such as the Eger region of Hungary, but should not be confused with limestone Tufa.

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Shale is a fine-grained sedimentary rock that weathers into a clay-rich soil, while schist and slate are metamorphic rocks with distinct planes that break into sheets. Schist is coarser than slate and can drain well, especially if the planes are vertically inclined, such as in the Douro and Central Otago.

Anyone seriously interested in wine must have heard of the Mosel’s legendary slate soils – so well-drained that even phylloxera can’t survive here.

Gravel soils work well in the Medoc – as it is a humid maritime climate, it is important that heavy rainfall can run away from the roots and during dry periods the roots must dig deep to find water.

What Kind Of Soil Do Grapes Need

Soil can cause all kinds of problems – acid soil can cause too much aluminum or copper to damage vine growth, excess salinity (salt) can. This is a significant problem in Australia, where much of the soil was once sea. In fact the soil provides a home for vine root pests such as phylloxera and nematodes.

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Another complication that is beginning to come to light is the effect that biological activity in the vineyard and winery also has on terroir and wine flavor. A research paper in Oregon (Bokulich et al 2016) found unique characters associated with different populations of microbes in both vineyard and wine types, both for AVAs (American Viticultural Areas) and for individual vineyards. And in Croatia, Radić et al (2012) showed that even different weed species in the vineyard were associated with different mycorrhizal associations in vine roots.

This is another complication of the terroir picture and how soil and site affect what we taste. (Mycorrhiza is a mutually beneficial symbiotic relationship between a fungus and a plant. The fungus colonizes plant cells and obtains carbohydrates while improving the plant’s water and nutrient uptake, especially phosphate, which most plants can’t readily obtain. .This type of symbiosis is incredibly ancient and clearly beneficial as 92% of all plant families, including grapes, form such relationships).

This is just a small snapshot of the complexities of selecting and managing soil to grow the best grapes. Fortunately for many growers, millennia, if not centuries, of wisdom can help, and science can often come to the rescue in new regions. There is no doubt that soil is important to making good wine, but it is very clear that there is no simple answer to the question of what makes good vineyard soil.

Caroline Gilby is a Master of Wine and a scientist by training. She is a wine writer with a passion for the wines of Central and Eastern Europe and contributes to several wine books, magazines and websites. Grapes grow in many types of soil. Well-drained, deep, fertile loams are excellent, but grapes thrive on soils that contain clay, pebbles, gravel, shale, and sand. Gravel soils are generally well-drained and absorb and reflect the sun’s heat, providing heat to the vines.

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The best fertilizers for grapes are well-rotted manure or compost made with large amounts of straw-y manure applied as mulch during the growing season. Apply compost or straight, well-rotted manure in the fall at a rate of 15 to 20 pounds per 100 square feet. In most cases, no other fertilizers are required. Vineyards given this treatment produced up to 30 percent more fruit than those fertilized with a commercial preparation.



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