Next to climate and grape variety, one of the most important factors influencing wine quality. The different soil types have developed over millions of years through physical and chemical weathering of rocks and through humification of organic matter. In physical weathering, natural forces such as wind, water, heat, cold and frost initially cause the mechanical disintegration of the rock formations into clods and gravel. Strong temperature opposites, friction and shear forces as well as frost blasting by frozen water play an important role in this process. Chemical weathering processes such as oxidation, dissolution processes and acid attacks attack the mineral lattice structure of the rocks. In the process, easily water-soluble minerals such as carbonates (inorganic salts and organic esters of carbonic acid) and sulphates are dissolved first, and the rock slowly decomposes into grit, sand, silt or clay. Every rock, even the hardest granite or quartz will eventually decompose to dust, even if it takes many millions of years.
Organic substances from plant remains, animal residues from worms, insects and small animals of all kinds, as well as dead microorganisms such as algae, bacteria and fungi, are transformed into humus. In the process, the nitrogen compounds essential for plant growth (nitrates, ammonium) as well as other nutrients are released. Fungi and bacteria play the main role in the decomposition of organic residues such as wood, leaves, roots or animal corpses. Insects such as soil mites are important because of their crushing feeding activities. Earthworms play a decisive role in soil loosening, mixing and the formation of stable clay-humus complexes, which are formed in the earthworm gut and excreted as faeces. These contribute to the structural stability of the soil and can bind easily water-soluble nutrients, making them available to plants for longer.
Every soil consists of soil horizons (soil layers) with special properties. They are almost always horizontal and can be identified in the soil profile (vertical section of the soil in an excavation). The sequence is the essential criterion for determining the soil type. From top to bottom, a soil is divided into an O horizon (organic soil horizon) or also H-L-O horizon (peat from plant remains, litter) and a three-part mineral horizon with A horizon, B horizon and C horizon. Horizons are mixed by deep mechanical tillage. Depending on climate and erosion impact, the A or B horizon may be absent or only marginally developed. The individual horizons are designated with symbols. The main symbols are written in capital letters, the additional symbols (features due to soil formation or pedogenic features) are written in lower case letters after the main symbol:
As an example, an Ae horizon: a lightened, often grey-bleached zone beneath the humic topsoil. It is formed by strong soil acidification and the associated displacement of complex iron-humus compounds. Below this is a wash-in zone, an illuvial horizon enriched with the washed-out substances of the Ae horizon. Depending on the predominant humus or iron compounds, a distinction is made between Bh- (h = humus) and Bs-horizon (s = backwater). Most of the vine root system is located at a depth of 20 to 50 centimetres (horizons A and B), but this is highly dependent on the soil type. In very old vines, roots can reach up to 15 metres deep and more.
In a vineyard, the horizons have usually already been mixed by tillage (rigolen = loosening of the soil). Rock subsoil, initial soil, tillage, fertilisation as well as water balance with a balanced relationship between the water storage capacity and water drainage characterise the vineyard location in addition to the local climate (microclimate or site climate) and give each vineyard site the typical and unmistakable character of its origin. The duration of the vegetation cycle, the orientation of the exposure (sunlight) and the local site climate on the slope, the existing soil conditions, the humus and lime content and the water supply influence the choice of the most suitable grape varieties.
The frequently used catchphrase "wine quality is primarily created in the vineyard/vineyard (and can only be improved to a small extent in the cellar)" can be read on many winegrowers' websites and is 100% valid. The well-known geologist and wine book author James E. Wilson aptly writes in his book "Terroir - Key to Wine": "The soil is the soul of the vine". However, the direct relationship between rock, grape variety and wine character is probably only marginally pronounced today due to the uniform use of often shallow-rooted rootstocks with heavy mineral fertilisation and the use of new viticultural cellar methods. In the vineyards of the past, which were fertilised only sparingly and mostly organically, with their old vines planted ungrafted and often rooted deep into the rock, this relationship was certainly much more pronounced.
The French in particular recognised the importance of the interplay of climate-rock-soil-location-small climate and grape variety very early on and elevated this to their philosophy, so to speak, in the creation of the term terroir. The terroir with the grape varieties best suited to it is defined by wine law in the classification of wine-growing regions as Appellation d'Origine Protégée (AOC/AOP). This is a clear difference to the philosophy in Germany and Austria, for example, where great (sometimes too much) importance is attached not to the location but mainly to the grape variety and the single-varietal vintage wines produced from it. A rethink has already begun, however.
In terms of wine quality, it can be a great advantage if the vines have to drill their roots as deep as possible into the soil because of stony ground. The ability of soils to act as ion exch angers, i.e. to exchange nutrient salts in the soil solution for the protons (H+) and anions (OH-) given off by the plant, is what makes it possible to supply the roots with essential nutrients and trace elements in the first place. The minerals absorbed are found in the overall extract of a wine. The vine needs about twenty essential trace elements and the main nutrients to thrive optimally. As a permanent crop, it is less dependent on fertile soils than annual crops. There are sites with very poor soils where high-quality wines grow. However, this does not mean that the fewer nutrients available, the better the wine quality.
A lack of nitrogen and amino acids in the must can hinder the yeasts during fermentation and cause fermentation defects. Among other things, this can manifest itself in the wine defect UTA (atypical ageing tone). The harmonious composition of the nutrients in the soil, the availability of water and nutrients as well as the aggregate state and rootability are much more important for the suitability of a soil. Plant or soil tests using the EUF method can detect nutrient deficiencies and, if necessary, correct them by fertilisation. A comprehensive classification or determination of the soil quality for agricultural use or specifically for viticulture is carried out by means of bonitur.
On calcareous soils with pH values above 8, the high calcium content in the soil impedes the uptake of other doubly positively charged ions such as nitrogen compounds, magnesium or the trace elements boron, iron, manganese or zinc, so that lime chlorosis or other physiological deficiency symptoms can occur, even with normally sufficient nutrient contents in the soil. Especially at the beginning of the growth cycle, the nitrogen content (in the form of nitrate and ammonium) in the soil should be sufficient. As a basic rule, basic (alkaline) soils with high pH values above 8 (for example, limestone, chalk and marl soils with mostly high levels of calcium and magnesium) produce wines with higher acidity, while acidic soils with low pH values below 6 to 4 (for example, granite, quartz sand) produce wines with lower acidity levels. Trials with increased potassium applications have shown that vines respond with increased malic acid production. To compensate for the increased influx of positive potassium ions, the plant produces negatively charged acid anions (malic acid). However, other causes (independent of vintage or ripeness-related acidity levels) naturally contribute to the acidity in the wine.
A good vineyard soil should be rather lean, medium to deep, well aerated, water-permeable and not compacted, rich but not too rich, not too humus-rich but rich in mineral components. The best sites are so-called slope sites, because this creates an almost vertical angle of incidence for the sun's rays in late summer, and thus the maximum amount of irradiation can be utilised. The best location on a slope is the wind-calm concave centre (belly, navel, kidney), where the highest temperature sums are reached and the soil is usually well-drained. Soil colour also plays an important role, because dark soils absorb the sun's heat more quickly and extensively, while light soils reflect light, so such soils do not heat up as quickly or as much. The suitability of an area for viticulture is called viticultural suitability, which can be determined on the basis of a catalogue of criteria.
In soil science, soil type refers to different manifestations of soils which, as a result of the processes of pedogenesis (soil formation), have produced matching characteristics in the form of soil horizons, thus showing a similar stage of development. While the soil type describes the appearance of a soil as a result of soil formation, soil types (also soil texture or grain size) are differentiated according to the grain size composition of the mineral soil substance. The main soil types are sand, silt, clay and loam.
Italian term for weathered sandstone with a high proportion of calcium carbonate (limestone) in Tuscany, predominant in the central and more southern parts of the Chianti region. See below under limestone.
Alluvium/Alluvion (alluvial soil)
Alluvial sediment (loose materials) washed up and deposited by water. Alluvium is also another name for the Holocene, the youngest and, since the end of the last ice age about 10,000 years ago, continuing earth age until today. Alluvial soils are mostly fine-grained, very fertile soil types that develop in the floodplains and estuaries of rivers. They consist of soil particles that have been washed up and sedimented when the water calms down.
Depending on the sinking velocity of the soil particles carried in the water and the flow velocity of the floodwater, they consist of clayey mud, silt, sand or, in riparian areas with high runoff velocities and strong erosion dynamics, gravel and boulders. Despite being predominantly stony and sandy, as is the case in the French Médoc region, among others, these soils are very well suited for viticulture. The secret of the sites there are the clay lenses inside the alluvial gravel terraces, deposited during various floods and covered with sand and gravel, which can store water. Such clay layers are literally sought out by the vine roots in search of water.
Mostly black over grey to dark green rock, formed by the metamorphic transformation of basalt (see below) under high pressure and temperature conditions. It consists of up to 50% representatives of the amphibole group, such as hornblende (see below) or chermakite, and up to 40% of other minerals such as garnet and quartz, as well as ores such as magnetite and pyrite.
Named after the Greek wind god Aeolus, caused by the wind. Aeolian transport causes fine material such as loess, silt or clay to be released from the parent material such as unconsolidated rock and transported over greater distances by the wind. Aeolian weathering is the removal of rock by wind-moved grains of sand, fine gravel, etc. with the effect of a sandblast. This creates an aeolian weathering soil.
The geological term describes a pink to reddish, coarse-grained sandstone with a high proportion of feldspar, which occurs mainly in dry, water-scarce areas. It leads to the coarser-grained granite rocks.
Soils formed from river deposits that are periodically flooded. Such soils occur, for example, in the Danube, Moselle and Rhine floodplains. When they are no longer flooded, they develop into brown soils and parabrown soils. These soils are usually nutrient-rich, biologically active and fertile.
Basic effusive rock (cooled magma) consisting of feldspar, hornblende, olivine and magnetite, which was formed during the melting of the Earth's mantle. It contains a lot of lime and soda and is rich in minerals. The hard, slowly weathering rock forms good soils and produces wines with appealing acidity. It is particularly suitable for white wines from the varieties Chardonnay, Grüner Veltliner, Pinot Blanc, Sauvignon Blanc and Welschriesling. Such soils occur, for example, on the Mosel and the Middle Rhine (Germany) and in Styria (Austria).
Pumice (Bimsstein, Bimstuff)
This porous, glassy volcanic rock is formed by gas-rich volcanic eruptions in which the lava is foamed by water vapour and carbon dioxide. It is chemically no different from other lava, but is much lighter due to the trapped air. The colour varies from black and with increasing air content to grey and white. The name Bimstuff refers to the grain size, at least 75% must consist of volcanic ash. Soils made of pumice have a good water retention capacity and are very suitable for viticulture. It is found throughout the Greek island of Santorini, which was formed from a volcanic explosion. Similar to pumice is obsidian, but it contains much less carbon dioxide. See also under canava and below under volcanic rocks.
See below under slate.
Common name in Bordeaux for a very fine, siliceous soil. It occurs, for example, on the plateau of the French Entre-deux-Mers area.
These A-B-C soils develop mainly over low-calcareous but base-rich rocks such as granite, gneiss, greywacke, clay slate and clayey sandstone. Formation occurred under humid climatic conditions from humus-rich topsoil on low-calcareous silicate rock (ranker) with deciduous and mixed forest cover. The brown colouration in the B horizon is caused by iron oxides formed during the chemical weathering of iron-containing silicates. In this process, the acids released by the tree roots strongly contributed to the deep weathering of the B horizon. The lime content, stone content and water balance of brown earths can differ greatly. Depending on its nature, this can be an excellent soil for viticulture.
Parabraunerde differs from brown earth in that clay particles have been displaced from upper to deeper layers. This is a process that occurs when the soil acidifies. Calcium dissolution causes putty-like lime structures to disappear, so that the released clay particles are washed away with the seepage water into deeper soil layers. Parabrown soils mostly developed from pararendzines. Parabrown and brown soils are the most common soils in humid Europe. Loam and loess parabrown soils are among the most fertile soils.
Conglomerate with angular components (see below).
Variegated, mostly red sandstone with partly clayey alluvium. The red sandstone was formed from the erosion debris of mountains of the Palaeozoic era. It was deposited in a dry semi-desert climate in a large basin (Germanic Basin) in the centre of present-day Europe and later overlaid by sedimentary rocks such as Jurassic limestone or by fly loess. Such soils are found, for example, in the growing region of the Palatinate (Germany).
See under Terra Ross a and below under Rotliegendes.
Complex silicate compounds of white and reddish minerals that contribute about 60% to the composition of the Earth's crust. They contain iron, potassium, calcium and sodium. There are three main groups: potassium feldspar (adular, sanidine), soda-lime feldspar (albite, pericline, anorthite) and microcline. Weathering produces base-rich clay minerals that can release mineral-bound ions as nutrients to the vine. Feldspar is one of the...
For my many years of work as an editor with a wine and culinary focus, I always like to inform myself about special questions at Wine lexicon. Spontaneous reading and following links often leads to exciting discoveries in the wide world of wine.Dr. Christa Hanten
Fachjournalistin, Lektorin und Verkosterin, Wien