1.4.1.b Which grape varieties are suitable to the plot's soil type?

What is the soil type?

What ratio of clays, sands and silts are present in each horizon?

The amount of each of these three entities (plus stone content) will directly determine the plot's soil category. A soil pit can be used to observe the different soil horizons. Each of these horizons has potentially varying properties. Soil composition impacts its behavior with respect to water, which in turn influences the depth at which the roots can grow and the soil's ability to warm up. It also influences several other factors: the biological activity of the soil, the ripeness that the grape variety can reach, the availability of nitrogen, the ease with which it can be tilled or not... Understanding one's soil is understanding one's vineyard.

Does the soil contain a high level of coarser-grained particles (gravel, pebbles...)?

Also called stone content, this index categorizes the soil type and gives a better understanding of its capacity to drain water. Additionally, gravel influence and soil temperature can be assessed. Indeed, having a significant amount of gravel close to the grape bunches can impact ripening. The heat is stored throughout the day and then released in the evening, thus improving the ripening process.

What is the roots usable depth?

The usable soil depth determines how far the vine can penetrate in order to to harness resources and, as a consequence, how the vine will behave when faced with water stress.
This measure depends on the type of soil. Some swellable clays destroy young roots when saturated. In addition, the presence of a crust which blocks root development at a certain depth is possible. If this is the case, a grape variety that is very sensitive to water stress should be avoided or the crust should be broken up if possible.

What are the soil and subsoil water regimes like?

What is the soil water storage capacity (SSC)?

This value corresponds to a maximum water volume that the soil retains after a 48-hour resoaking period. This value is expressed in mm of water. It does not mean that the water is available for the plant.

What is the maximum usable reserve (MUR) for the soil?

This is the maximum amount of water available to the vine in all horizons. It is measured in mm or l/m2.
Some key values: low from 30 to 60 mm, high from 100 to 150 mm.

What is the soil water buffer (RUM/CSE) ?

This indicates whether the soil will retain a lot of water during a rainfall and whether or not it is availible for the vine. This data gives an indication of how the soil will behave after heavy rainfall and consequently if it is able to regulate the water supply to the vines.
Example: RUM/CSE < 40% means that the soil retains a lot of water but releases little to the plant. The water reserve is well regulated.
Conversely, if RUM/CSE> 60% water is highly available, there is little regulation. The plot is therefore more sensitive to the vintage effect.
These values are generally provided in conjunction with the soil pit interpretation.

Is there a difference of permeability between the different horizons ?

In some cases, there is a very real difference in permeability between the horizons. If the soil permeability is low, the water does not flow downwards or if it does, only little amounts do, so it moves horizontally. Its flow regime and therefore the quality of the wine produced is strongly dependent on the plot's topography and the horizons' thickness. Indeed, the slope will condition the water flow. It can facilitate drainage, which is often very beneficial depending on the soil type, especially if the horizon is impermeable.

Is this soil likely to suffer from severe water stress during certain periods?

On free-draining soils such as sand-based soils, hydric stress can be significant. It is better to choose grape varieties that require little water. Moderate water stress is always beneficial for wine quality.

Is this parcel at risk of becoming waterlogged?

If a watercourse is nearby or if there is a deep impermeable horizon, or, indeed, if the parcel is in a basin, there is a risk of saturation, which causes root asphyxia. If the water excess is temporary, there will not be any catastrophic side effects (depending on the period). On the other hand, if the vine is permanently saturated, it will not experience any benefical hydric stress and some of its roots may even perish.

Does the soil heat up easily?

This parameter will affect how early the grapes ripen and the biological activity of the soil's microorganisms. It depends on the type of soil and the water regime. A clay soil will be richer in water and will be colder.
A sandy soil is very free-draining and easier to warm up, as is a soil rich in gravel. Early-ripening grape varieties are well suited to colder soils in a northern climate, but again it all depends on the climate of the appellation.

How much nitrogen is availible in the soil ?

Nitrogen availability directly conditions the plot's vigor and cryptogamic disease risks. A very vigorous plot is generally more affected by cryptogamic diseases.
Nitrogen availability depends on both the soil's richness and its biological activity. The latter is conditioned by the soil's warmth. As the temperature increases, so does the level of biological activity.

Other parameters are also important for biological activity such as soil pH.
Nitrogen has additional side effects, notably on the yield and the way the soil is maintained. For example, on a poor soil, grassing should be avoided to limit competition with the vine for resources.