The supply of water in the right quantity and at the best possible time is an important prerequisite for the growth of the vines and indispensable for photosynthesis. This is done naturally by precipitation (rain), the required amount is usually between 500 and 750 millimetres per year (depending on the climate). With ideal soil conditions, however, larger amounts of precipitation can also be tolerated. In the Portuguese Vinho Verde area, for example, the amount of precipitation is 1,500 millimetres. In addition to the amount, the time during the vegetation cycle also plays an important role.
The "right" amount of water is important, too little moisture can lead to water stress (also called drought stress), and excessive rainfall in turn leads to excessive vegetation (foliage growth). Especially during the grape harvest rain is undesirable and leads to poor wine quality due to the dilution of grape juice. In extreme cases, the so-called wetness stress occurs, in which the berries swell or even burst open and as a result the grape juice can oxidise or, in extreme cases, already ferment. In addition, too much moisture promotes infestation by certain microorganisms such as fungi or bacteria. In order to take any necessary measures, the soil moisture is measured by the Tensiometer.
Decisive for a good water balance is the type of soil, which is ideally loose and deep, so that the roots can spread out far or dig deep into the soil and thus easily absorb nutrients and water. It is important to have a good balance between water storage capacity and water withdrawal. Waterlogging is extremely harmful to the roots, especially after growth in spring, and leads to poor fruit set and trickling during flowering. Good water drainage can be promoted by planting vegetation, covering the soil with mulch or by artificial drainage. The second important criterion is the water storage capacity in the subsoil. These are the layers above the sediment or bedrock, which are usually denser and deeper.
The subsoil lies below the main layer of nutrients through which the roots run. Clay, for example, is ideally suited because it retains the moisture in the soil, counteracts evaporation (evaporation of water and thus dehydration) and, in addition, only passes on water to the roots in a limited and metered amount. Unlike rain, however, dew does not contribute much to the water supply of the vine. Rather, dew promotes the development of fungi - in most cases this is undesirable(mildew, green rot, black rot), but it is also beneficial for the production of noble sweet wines through botrytis (noble rot). The latter (the prime example is the French area of Sauternes) often occurs near bodies of water.
Enrichment with water-soluble salts can lead to salinisation of the soil with a negative water balance. This means that evaporation during the vegetation cycle (six to nine months) of a year is greater than precipitation. In any case, measures are necessary to improve the retention of rainwater. The aim is to keep the net consumption to zero, i.e. not to use more water than precipitation can (can) be collected in the soil.
Artificial irrigation of vineyards was already common in ancient times, for example in ancient Egypt. Today, the method is absolutely necessary in climatically hot countries with too little precipitation (maximum 300 mm), especially in dry summer months with the risk of drought. It is mainly used in the production of table grapes and raisins. It is also common for newly planted vines that do not yet produce a yield.
In viticulture, however, this is extremely sensitive and a hotly debated topic. The method is widely used overseas in the countries of Egypt, Argentina, Azerbaijan, Australia, Chile, Israel, California, Peru and South Africa, and in Europe in southern countries such as Greece, Spain and Portugal. In some of these countries, it is the only way to keep the vines alive and thus prevent drought damage, which leads to unpleasant bitter notes and acidity deficits. The negative result is often fruity but undemanding mass wines produced in large quantities.
A common form is drip irrigation, in which water droplets are emitted from tubes permanently installed in the ground at adjustable intervals at perforated points on all vines. Fertigation (irrigation fertilization) is also used in this case. A second form is flooding, in which water from a channel is led between the rows of vines and seeps away. Special forms are Partial rootzone drying (partial root drying) and regulated deficit irrigation.
The EU allows its member states to set up their own regulations to achieve optimum quality of quality wines: "Irrigation of vineyards is basically aimed at increasing quality and is only possible if the environmental conditions justify it". However, this is a relatively imprecise regulation which is difficult to measure or control. In countries such as Germany and Austria, the methods are regulated on a wine-growing region-specific basis, and here the focus is usually on improving quality.
All aids, work and measures in the vineyard during the vegetation cycle can be found under vineyard care. Complete lists of the numerous cellar techniques, as well as a list of the types of wine, sparkling wine and distillate regulated by wine law can be found under vinification. Comprehensive wine law information can be found under the keyword wine law.